阅读说明：本技术 基于二维量子点的光电探测器 (Photoelectric detector based on two-dimensional quantum dots ) 是由 奈杰尔·皮克特 斯图尔特·斯塔布斯 纳瑟莉·格雷斯蒂 于 2019-08-23 设计创作，主要内容包括：一种光电探测器(200)包括：底部电极(210)；布置在该底部电极上的中间层(220)；布置在该中间层上的光吸收层(230),该光吸收层具有一种或多种电荷传输材料,和分散在该一种或多种电荷传输材料中的多个二维量子点(2D QD)；以及布置在该光吸收层上的顶部电极(240)。一种异质结构光电探测器(300)包括：底部电极(310)；布置在第一电极上的第一光吸收层(320),该第一光吸收层具有第一光吸收材料；布置在该第一光吸收层上的第二光吸收层(330),该第二光吸收层具有第二光吸收材料；以及布置在该第二光吸收层上的顶部电极(340),该第一或第二光吸收材料中的至少一种是多个二维量子点(2D QD)。(A photodetector (200) comprising: a bottom electrode (210); an intermediate layer (220) disposed on the bottom electrode; a light absorbing layer (230) disposed on the intermediate layer, the light absorbing layer having one or more charge transport materials, and a plurality of two-dimensional quantum dots (2D QDs) dispersed in the one or more charge transport materials; and a top electrode (240) disposed on the light absorbing layer. A heterostructure photodetector (300) includes: a bottom electrode (310); a first light absorbing layer (320) disposed on the first electrode, the first light absorbing layer having a first light absorbing material; a second light absorbing layer (330) disposed on the first light absorbing layer, the second light absorbing layer having a second light absorbing material; and a top electrode (340) disposed on the second light absorbing layer, at least one of the first or second light absorbing materials being a plurality of two-dimensional quantum dots (2D QDs).)

1. A photodetector, the photodetector comprising:

a first electrode;

an intermediate layer disposed on the first electrode;

a light absorbing layer disposed on the intermediate layer, the light absorbing layer comprising:

one or more charge transport materials; and

a plurality of two-dimensional quantum dots (2D QDs) dispersed in the one or more charge transport materials; and

a second electrode disposed on the light absorbing layer.

2. The photodetector of claim 1, wherein the thickness of the intermediate layer is in a range of about 1nm to about 1000 nm.

3. The photodetector of claim 1 or claim 2, wherein the light absorbing layer comprises about 10% to about 95% by volume of the 2D QDs.

4. The photodetector of any one of claims 1 to 3, wherein the light absorbing layer comprises about 5% to about 90% by volume of the one or more charge transport materials.

5. The photodetector of any one of claims 1 to 4, wherein a thickness of the light absorbing layer is in a range of about 10nm to about 2 microns.

6. The photodetector of any one of claims 1 to 5, wherein the 2D QDs have a thickness of about 1 to about 5 monolayers of atoms or molecules and a lateral dimension sufficient for the 2D QDs to be within quantum confinement.

7. A heterostructure photodetector, comprising:

a first electrode;

a first light absorbing layer disposed on the first electrode, the first light absorbing layer comprising a first light absorbing material;

a second light absorbing layer disposed on the first light absorbing layer, the second light absorbing layer comprising a second light absorbing material; and

a second electrode disposed on the second light absorbing layer.

8. The heterostructure photodetector of claim 7, further comprising an intermediate layer disposed between the first electrode and the first light absorbing layer.

9. The heterostructure photodetector of claim 7 or claim 8, further comprising a transition layer disposed between the first light absorbing layer and the second light absorbing layer, the transition layer comprising a combination of the first light absorbing material and the second light absorbing material.

10. The heterostructure photodetector of any one of claims 7 to 9, wherein the first light absorbing material is a plurality of two-dimensional quantum dots (2D QDs), a plurality of two-dimensional nanoplatelets (2D nanoplatelets), or a plurality of conventional QDs.

11. The heterostructure photodetector of any one of claims 7 to 10, wherein the second light absorbing material is a plurality of 2D QDs, a plurality of 2D nanosheets, or a plurality of conventional QDs.

12. The heterostructure photodetector of any one of claims 7 to 11, wherein the first light absorbing material is a plurality of 2D nanoplatelets and the second light absorbing material is a plurality of 2D QDs.

13. The heterostructure photodetector of any one of claims 7 to 11, wherein the first light absorbing material is a first plurality of 2D QDs and the second light absorbing material is a second plurality of 2D QDs.

14. The heterostructure photodetector of any one of claims 7 to 11, wherein the first light absorbing material is a plurality of 2D QDs and the second light absorbing material is a plurality of conventional QDs.

15. The heterostructure photodetector of any one of claims 7 to 11, wherein the first light absorbing material is a plurality of conventional QDs and the second light absorbing material is a plurality of 2D QDs.

16. The heterostructure photodetector of any one of claims 7 to 11, wherein the first light absorbing material is a plurality of 2D QDs and the second light absorbing material is a plurality of 2D nanoplatelets.

17. The heterostructure photodetector of any one of claims 7 to 16, wherein a valence band and a conduction band of the first light absorbing material are offset from a valence band and a conduction band of the second light absorbing material to generate a built-in electric field.

18. The heterostructure photodetector of any one of claims 7 to 17, wherein a combined thickness of the first light absorbing layer and the second light absorbing layer is in a range of about 50nm to about 800 nm.

19. The heterostructure photodetector of any one of claims 7 to 18, wherein one of the first and second light absorbing layers further comprises a charge transport material.

20. The heterostructure photodetector of any one of claims 7 to 12 and 16 to 19, wherein one of the first and second light absorbing materials is a plurality of 2D nanoplatelets having a thickness of 1 to 10 atomic or molecular monolayers and a lateral dimension extending beyond a quantum confinement range.

1. The field of the invention.

The present invention relates generally to semiconductor nanoparticles commonly referred to as "quantum dots" (QDs). More particularly, the present invention relates to quantum dots comprising two-dimensional materials and their use in photodetectors.

2.A description of the related art including the information disclosed in accordance with 37 CFR 1.97 and 1.98.

A photodetector is a device that generates an electrical signal in response to incident photons. Photodetectors or photosensors respond to the intensity of light or other electromagnetic energy incident thereon. Solid state photodetectors have a p-n junction that converts photons of light into an electrical current. The absorbed photons form electron-hole pairs in the depletion region. Photodiodes, photoconductors, and phototransistors are examples of photodetectors. Solar cells are photodetectors in the sense that they convert some of the light energy they absorb into electrical energy, the amount of which can be sensed by appropriate circuitry.

Photodiodes are typically based on p-n junctions. In a photodiode, electron-hole pairs are formed when photons of sufficient energy strike the device. If absorption occurs in the depletion region of the junction or one diffusion length from it, the built-in electric field (build-in electric field) of the depletion region causes carriers to be swept out of the junction, where holes move towards the anode and electrons move towards the cathode, thereby generating a photocurrent.

A photoconductor is a device that detects a temporary change in the conductivity of a semiconductor caused by irradiation of light. The photons produce optically excited carriers that are extracted by an electric field generated by a bias applied between the electrodes.

The phototransistor is similar to a photodiode with the addition of another n-type region. The phototransistor includes a photodiode with internal gain. It can be represented as a bipolar transistor enclosed in a transparent envelope so that photons can reach the base-collector junction. Electrons generated by photons in the base-collector junction are injected into the base, thereby amplifying the current.

These three types of photodetectors each have different characteristics and can therefore be used for different applications. The phototransistor and photodiode detect at similar rates, but the response time of the phototransistor is slow (microseconds, relative to nanoseconds with respect to the photodiode). The phototransistor has a higher gain and the temperature of the photodiode varies less.

Photodetectors may be used in different configurations. A single sensor may detect the overall light level. As in a spectrophotometer or line scanner, a 1-D array of photodetectors may be used to measure the distribution of light along the line. A 2-D array of photodetectors may be used as an image sensor to form an image from a pattern of light incident thereon.

The photodetector or array is typically covered by an illumination window, which may have an anti-reflection coating.

There are many performance indicators (so-called "valuable figures") that can be characterized or compared to photodetectors. One performance indicator is the spectral response (response of the photodetector as a function of photon frequency). Another performance indicator is quantum efficiency (QE; the number of carriers (electrons or holes) generated per photon). Yet another performance indicator is responsivity (R; output current divided by total optical power falling on the photodetector_PhotonIn which E_PhotonIs the photon energy in eV). Yet another performance indicator is noise equivalent power (NEP; minimum detectable power, i.e. the optical signal under whichThe telecom noise ratio in the detector is equal to one (0dB) when the bandwidth is limited to 1 Hz). Yet another performance indicator is specific detection rate (D ═ x; the square of detector area a times frequency bandwidth B is divided up by the noise equivalent power [ √ (AB) ])]/NEP). Yet another performance metric is gain (G; the output current of the photodetector divided by the current directly generated by photons incident on the detector, i.e., the built-in current gain). Yet another performance indicator is dark current (I)_d(ii) a Current flowing through the photodetector even in the absence of light). Yet another performance index is the response time (τ; time required for the photodetector to go from 10% to 90% of the final output). Yet another performance indicator is the noise spectrum (the inherent noise voltage or current that varies with frequency; this can be expressed in terms of noise spectral density). Yet another performance metric is non-linearity (the RF output is limited by the non-linearity of the photodetector). Yet another performance indicator is spectral selectivity (the cut-off wavelength beyond which the response signal is comparable to or less than the noise level.

In order to achieve high performance of the photodetector, a combination of high responsivity, short response time, high specific density and a broad spectrally selective wavelength range is desirable.

Solution processable photodetectors with sensitivity across the Ultraviolet (UV) to Near Infrared (NIR) range are of increasing interest for applications such as imaging sensors. Of particular interest is the range of 1-1.8 μm, where the water absorption is low.

The potential use of colloidal Quantum Dots (QDs) as light absorbers in photodetection applications has been recognized, with research focused primarily on PbS QDs containing toxic lead.

Due to their combination of optical properties and mechanical flexibility, 2D materials, including graphene and Transition Metal Dichalcogenides (TMDC), have been investigated as light absorbers for photodetection applications. Graphene-based photodetectors have been extensively studied and demonstrated to exhibit high carrier mobility, excellent stability, high mechanical strength, and spectral response across visible to far infrared. However, difficulties in opening the band gap of graphene result in high dark current, limiting its applicability to photodetection. Layered TMDC offers many advantages, including a bandgap that can be tuned by the number of layers. They are also compatible with complementary metal-oxide-semiconductor (CMOS) technology, which can be used to build integrated circuits, enabling the development of multifunctional high-performance photodetectors with low power consumption.

Due to its narrow thickness (which limits light absorption), it is currently difficult to produce photodetectors with high responsivity, broadband spectrum, and high detectivity using a single TMDC. The use of highly absorbing sensitizers can help improve the light absorption efficiency, but the sensitizer needs to be thin enough to retain the advantages of the 2D material. High carrier mobility and a band structure well matched to TMDC are also desirable for efficient charge separation and transfer.

Colloidal QDs have been used as sensitizers in combination with TMDC chips to achieve sensitive, fast and broadband photodetectors. For example, PbS QD has been associated with WSe₂The nano-sheet is used in combination [ C.Hu et al, adv.Funct.Mater.2017,27,1603605 ]]And CdS/ZnS QD has been associated with WS₂Monolayer combinations [ a.baulesbaa, k.wang, m.mahjouri-Somani, m.tiana, a.a.puretzky, i.ivanov, c.m.rouleau, k.xiao, b.g.summter and d.b.grohegan, j.am.chem.soc, 2016,138,14713]。

The nanoplatelets have a larger contact area compared to QDs, and thus 2D nanoplatelets with materials such as graphene and other layered materials have been investigated along with mixed devices of TMDC. For devices with a 2D heterostructure as the sensitizer, the formation of a Schottky barrier (Schottky barrier) at the heterostructure interface can result in an intrinsic electric field, providing efficient charge transfer at the interface.

Thus, both colloidal QDs and 2D nanoplates can provide advantages for photodetector applications.

Traditionally, crystalline silicon has been used for photodetection applications. However, its absorption is limited to below 1.1 μm, which means that it cannot absorb most of the Infrared (IR) spectrum. In addition, its absorption is very weak in its spectral range, only exceeding 104cm at 500nm^-1. The ultrashort absorption wavelengths in silicon in the ultraviolet region at wavelengths associated with the detection of skin cancer results in high recombinationGenerates electron-hole pairs near the surface states of (a). This limits the UV sensitivity in standard silicon devices. Therefore, there is a great interest in materials that can absorb light beyond the silicon range.

Epitaxially grown QDs have been used for photodetection applications, but can be difficult to process. The all-organic semiconductor can provide convenient treatment for photoelectric detection application. Until recently, however, there have been few small organic molecules or polymers available with narrow band gaps that are suitable for fabricating photodiodes in the near infrared range.

QD photodiode devices can be tuned to near infrared ranges beyond the spectral range of organic semiconductors, but the main problem is the dependence on QDs based on toxic heavy metals (such as lead or cadmium).

Photodetectors that incorporate light absorbers based on 2D materials (e.g., graphene and TMDC) have been explored. Advantages include its unique optical properties and mechanical flexibility. Other desirable properties include high carrier mobility, chemical stability, mechanical strength, and spectral response that can be tuned from the visible to the far infrared region. In particular, TMDC based photodetectors may be tuned by varying the number of layers. Heterostructures of two different layered materials have also been explored. Weak van der waals interactions between two advantageously arranged materials can produce high quality heterojunctions without causing problems due to lattice mismatch between the two materials.

Heterostructure devices comprising CdSe-based 2D nanoplates and graphene have been described. Robin, e.lhuillier and b.dubertet, MRS adv.,2016,2187; robin, e.lhuillier, x.z.xu, s.ithuria, h.aubin, a.oweerghi and b.dubertret, sci.rep.,2016,6,24909 ]. The device utilizes the strong absorption rate of the nano-plate and the high carrier mobility of the graphene. The 2D nano-plates have a thickness of 1-5nm and a lateral dimension of up to 1 μm, such that the lateral dimension is much larger than the Bohr radius. A disadvantage of these nanoplates is that they do not provide bandgap tunability.

One problem that must be addressed for photodetectors incorporating 2D material layers is the elimination of deep trap states that are detrimental to response speed.

Although many photodetector devices incorporating 2D materials have been reported, the prior art relies on exfoliation or CVD deposition processes that are difficult to scale.

Background

Summary of The Invention

Photodetectors according to aspects of the present disclosure may include a plurality of semiconductor nanoparticles having lateral dimensions within a quantum confinement range (quantum confinement domain) and a thickness of 1 to 5 atomic or molecular monolayers (including endpoints) ("2D quantum dots" or "2D QDs").

Some of the advantages of using QDs in photodetector applications include strong, tunable absorption spectra and solution processability. Some advantages of using 2D materials include high contact area and surface flatness, adjustability of absorption through material thickness, high mobility, and high transparency.

The combined advantages of QD and 2D materials may be achieved by using 2D QDs instead of other conventional forms of QDs (i.e., 0D spherical QDs, 1D QDs (e.g., nanorods), or 3D QDs (e.g., nanocubes, nanotubules, etc.)) and/or 2D layered materials. Additional absorption tunability can be achieved by modifying the QD thickness, and the 2D QDs can be composed of non-toxic materials, mitigating concerns over the toxicity of heavy metal (e.g., cadmium and lead) based QDs.

Solution processable photodetectors are of particular benefit in sensor applications.

In a first aspect of the present invention, there is provided a photodetector comprising: a first electrode; an intermediate layer (interlayer) disposed on the first electrode; a light absorbing layer disposed on the intermediate layer, the light absorbing layer comprising: one or more charge transport materials; and a plurality of two-dimensional quantum dots (2D QDs) dispersed in the one or more charge transport materials; and a second electrode disposed on the light absorbing layer.

The thickness of the intermediate layer may be in the range of about 1nm to about 1000 nm. The light absorbing layer may include about 10% to about 95% by volume of the 2D QDs. The light absorbing layer may include about 5% to about 90% by volume of one or more charge transport materials. The thickness of the light absorbing layer may be in the range of about 10nm to about 2 microns. The 2D QDs may have a thickness of about 1 to about 5 atomic or molecular monolayers and lateral dimensions sufficient to keep the 2D QDs within quantum confinement.

In a second aspect of the present invention, there is provided a heterostructure photodetector comprising: a first electrode; a first light absorbing layer disposed on the first electrode, the first light absorbing layer including a first light absorbing material; a second light absorbing layer disposed on the first light absorbing layer, the second light absorbing layer comprising a second light absorbing material; and a second electrode disposed on the second light absorbing layer.

The heterostructure photodetector may further include an intermediate layer disposed between the first electrode and the first light absorbing layer. The heterostructure photodetector can further include a transition layer disposed between the first light absorbing layer and the second light absorbing layer, the transition layer comprising a combination of the first light absorbing material and the second light absorbing material. The first light absorbing material may be a plurality of two-dimensional quantum dots (2D QDs), a plurality of two-dimensional nanoplatelets (2D nanoplatelets), or a plurality of conventional QDs. The first light absorbing material may be a plurality of two-dimensional quantum dots (2D QDs). The first light absorbing material may be a plurality of two-dimensional nanoplatelets (2D nanoplatelets). The first light absorbing material may be a plurality of conventional QDs. The second light absorbing material may be a plurality of 2D QDs, a plurality of 2D nanosheets, or a plurality of conventional QDs. The second light absorbing material may be a plurality of 2D QDs. The second light absorbing material may be a plurality of 2D nanoplatelets. The second light absorbing material may be a plurality of conventional QDs. In an embodiment, the first light absorbing material is a plurality of 2D nanoplatelets and the second light absorbing material is a plurality of 2D QDs. In an embodiment, the first light absorbing material is a first plurality of 2D QDs and the second light absorbing material is a second plurality of 2D QDs. In an embodiment, the first light absorbing material is a plurality of 2D QDs and the second light absorbing material is a plurality of conventional QDs. It may be that the first light absorbing material is a plurality of conventional QDs and the second light absorbing material is a plurality of 2D QDs. It may be that the first light absorbing material is a plurality of 2D QDs and the second light absorbing material is a plurality of 2D nanosheets. The valence and conduction bands of the first light-absorbing material may be offset from the valence and conduction bands of the second light-absorbing material to generate a built-in electric field. The combined thickness of the first light absorbing layer and the second light absorbing layer may be in the range of about 50nm to about 800 nm. It may be that one of the first light absorbing layer and the second light absorbing layer further includes a charge transport material. It may be that one of the first and second light absorbing materials is a plurality of 2D nanoplatelets having a thickness of 1 to 10 atomic or molecular monolayers and a lateral dimension extending beyond the quantum confinement range.

Brief Description of Drawings

Fig. 1 illustrates the chemical structures of various charge transport polymers that may be combined with 2D QDs to produce 2D QD-sensitized organic photodiodes according to aspects of the present disclosure.

Fig. 2 is a schematic diagram of a photodetector device including 2D QDs within an organic photodiode according to aspects of the present disclosure.

Fig. 3 is a schematic diagram of a heterostructure photodetector including a first layer of 2D QDs and a second layer of 2D nanosheets, in accordance with aspects of the present disclosure.

Fig. 4 is a schematic diagram of a heterostructure photodiode including a first layer of 2D QDs and a second layer of 2D QDs in accordance with aspects of the present disclosure.

Fig. 5 is a schematic diagram of a heterostructure photodetector including a first layer of conventional QDs and a second layer of 2D QDs in accordance with aspects of the present disclosure.

Fig. 6 is a schematic diagram of a heterostructure photodetector including a first layer of 2D QDs and a second layer of conventional QDs in accordance with aspects of the present disclosure.

Fig. 7 is a schematic diagram of a heterostructure photodetector including a first layer of 2D nanoplates and a second layer of 2D QDs in accordance with aspects of the present disclosure.

Detailed Description

The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the subject matter of the disclosure, its application, or uses.

As used throughout, ranges are used as shorthand for describing each and every value that is within the range. Any value within the range can be selected as the terminus of the range. Unless otherwise indicated, all percentages and amounts expressed herein and elsewhere in the specification are to be understood as being percentages by weight.

For the purposes of the present specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims are to be understood as being modified in all instances by the term "about". The use of the term "about" applies to all numerical values, whether explicitly stated or not. The term generally refers to a range of numbers that one of ordinary skill in the art would consider to have a reasonable amount of deviation from the stated value (i.e., have an equivalent effect or result). For example, the term may be construed to include deviations of ± 10%, alternatively ± 5%, and alternatively ± 1% of a given numerical value, provided that such deviations do not alter the ultimate effect or result of the value. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.

It should be noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term "include" and grammatical variations thereof are intended to be non-limiting such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items. For example, as used in this specification and the following claims, the terms "comprising" (and forms, derivatives, or variants thereof, such as "comprising" and "including"), "comprising" (and forms, derivatives, or variants thereof, such as "including" and "including") and "having" (and forms, derivatives, or variants thereof, such as "having" and "having") are inclusive (i.e., open-ended) and do not exclude additional elements or steps. Thus, these terms are intended to encompass not only one or more recited elements or steps, but also other elements or steps not explicitly recited. Furthermore, as used herein, the use of the terms "a" or "an" when used in conjunction with an element can mean "one," but it is also consistent with the meaning of "one or more," at least one, "and" one or more than one. Thus, without further limitation, an element preceded by "a" or "an" does not exclude the presence of other, identical elements.

Over 20 years, the study of the properties of colloidal QDs and their optoelectronic devices has been of great interest. Recently, there has been an increasing interest in the unique properties of two-dimensional quantum dots (2D QDs). As used herein, "2D quantum dot" or "2D QD" refers to a semiconductor nanoparticle having a thickness of about 1-5 monolayers of atoms or molecules and a lateral dimension that results in a nanoparticle within quantum confinement — i.e., the electronic properties of the nanoparticle are different from those of the bulk material. As can be appreciated, the lateral dimensions that provide the nanoparticles with electronic properties indicative of quantum confinement ranges may vary between nanoparticles having different compositions. However, such lateral dimensions may typically be 1 to 100 nm. As used herein, the term "2D nanoplatelets" is used to describe particles having a thickness of 1 to 10 atomic or molecular monolayers, and wherein the lateral dimensions are sufficiently large that they extend beyond the quantum confinement range. As used herein, "monolayer quantum dot" or "monolayer QD" refers to a semiconductor nanoparticle that is a single monolayer thick and has lateral dimensions that result in a nanoparticle within quantum confinement. Compared to conventional zero-dimensional (0D) QDs, 2D QDs have much higher surface area to volume ratios, which increase as the number of monolayers decreases. The highest surface area to volume ratio was observed for single layer QDs. This can result in 2D QDs with very different surface chemistry than conventional QDs, which can be used for many applications. To date, most research on 2D QDs has focused on layered materials, such as carbon-based materials (e.g., graphene and graphene oxide)) And TMDC (especially MoS)₂、MoSe₂、WS₂And WSe₂) The QD of (1). However, recently, the synthesis of 2D nanoparticles of conventional semiconductor materials, such as II-VI (group) semiconductors, is of interest [ e.lhuillier et al, acc.chem.res.,2015,48, 22; riedinger et al, nat. mater, 2017,16,743]。

In some embodiments, the photodetector is a photodiode. Photodiodes are typically based on p-n junctions. In a photodiode, electron-hole pairs are formed when photons of sufficient energy strike the device. If absorption occurs in the depletion region of the junction or one diffusion length from it, the built-in electric field of the depletion region causes carriers to be swept out of the junction, with holes moving toward the anode and electrons moving toward the cathode, producing a photocurrent.

In some embodiments, the photodetector is a photoconductor. Photoconductors are devices that detect a temporary change in the conductivity of a semiconductor resulting from light irradiation. The photons produce optically excited carriers that are extracted by an electric field generated by a bias voltage applied between the photodetector anode and cathode electrodes.

In some embodiments, the photodetector is a phototransistor having a base-collector junction. The phototransistor is similar to a photodiode with the addition of an additional n-type region. The phototransistor includes a photodiode with internal gain. It can be represented as a bipolar transistor enclosed in a transparent envelope so that photons can reach the base-collector junction. Electrons generated by photons in the base-collector junction are injected into the base, thereby amplifying the current.

These three types of photodetectors each have different properties and can therefore be used for different applications. The detection rates of the phototransistor and photodiode are similar, but the response time of the phototransistor is slow (microseconds, relative to nanoseconds with respect to photodiode). The phototransistor has a higher gain, while the photodiode exhibits less temperature variation.

In at least one embodiment, a 2D QD-sensitized organic photodiode is employed. In at least one embodiment, a heterostructure photodetector is used that includes 2D QDs and 2D nanosheets (i.e., having lateral dimensions well outside the quantum confinement range). In at least one embodiment, a heterostructure photodetector is used that includes a first 2D QD layer and a second layer of 2D QDs of other materials. In at least one embodiment, a heterostructure photodetector is used that includes a conventional QD layer and a 2D QD layer.

Fig. 2 is a schematic diagram of a photodetector 200 according to aspects of the present disclosure. The photodetector 200 includes a bottom electrode 210, an intermediate layer 220 disposed on the bottom electrode 210, a layer 230 including 2D QDs dispersed in a charge transport material disposed on the intermediate layer 220, and a top electrode 240 disposed on the layer 230 containing 2D QDs. In the device configuration shown in fig. 2, one or more of the top and bottom electrodes 210, 240 may be transparent to allow light to pass therethrough. The bottom electrode 210 may include a transparent conductive oxide such as Indium Tin Oxide (ITO) and aluminum-doped zinc oxide (AZO). The top electrode 240 may include one or more low work function metals, such as aluminum and silver.

The intermediate layer 220 serves to improve electrical contact with the underlying bottom electrode 210. Intermediate layer 220 may be made of any suitable material, such as, for example, poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), MoO₃And metal oxides with zinc, titanium, vanadium or nickel. The thickness of the intermediate layer 220 may range from about 1nm to about 1000nm, alternatively from about 10nm to about 1000nm, and alternatively from about 100nm to about 1000 nm.

As schematically shown in fig. 2, a layer 230 comprising 2D QDs dispersed in a charge transport material may be produced by: the 2D QDs are dispersed (by blending or mixing) in one or more organic charge transport materials (electron and/or hole accepting and transporting organic materials) to form a heterojunction. Examples of suitable charge transport materials include, but are not limited to: [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), poly (3-hexylthiophene) (P3HT), poly (N-octyldithio [3,2-b:2 '3'd)]Pyrrole-alt (alt) -5, 6-bis (octyloxy) benzo [ c][1,2,5]Thiadiazole) (PDTPBT), poly [ (9, 9-dioctylfluorenyl-2, 7-diyl-co (4,40- (N-4-sec-butylphenyl)) diphenylamine)](TFB), poly (N, N ' -bis (4-butylphenyl) -N, N ' -bis (phenyl) -benzidine) (poly-TPD), poly (2-methoxy-5 (2 ' -ethylhexyloxy) -1, 4-phenylenevinylene) (MEH-PPV), poly (2, 5-bis (2 ' -ethylhexyloxy) -1, 4-phenylenevinylene) (DEH-PPV), poly [2,6- (4,4 ' -bis (2-ethylhexyl) dithieno [3,2-b:2 ', 3 ' -d)]Silole-alt-4, 7(2,1, 3-benzothiadiazole) (PSBTBT), poly [2,6- (4, 4-bis (2-ethylhexyl) 4H-cyclopenta [2, 1-b; 3, 4-b']Dithiophene) -alt-4, 7- (2,1, 3-benzothiadiazole)](PCPDTBT), poly (2, 3-didecyl-quinoxaline-5, 8-diyl-alt-N-octyldithio [3,2-b:2 '3' -d)]Pyrrole) (PDTPQx), dithieno [3,2-b:2,3-d]Pyrrole (DTP), poly (9, 9-n-dihexyl-2, 7-fluorenylenevinylene-alt-2, 5-thienylenevinylene (PFT), ethoxylated Polyethyleneimine (PEIE), 1-1-bis [ (di-4-tolylaminophenyl)]Cyclohexane (TAPC), C60, multi-walled carbon nanotubes and other polymers, the structure of some of which is shown in figure 1. In FIG. 1, the number-average molar mass M of PDTPBT_nCan be in the range of about 17kg mol^-1To about 19kg mol^-1Within the range of (1). Further, in FIG. 1, M of PDBF_nCan be in the range of about 11kg mol^-1To about 13kg mol^-1Within the range of (1). Furthermore, in FIG. 1, M of PDTD_nCan be in the range of about 30kg mol^-1To about 35kg mol^-1Within the range of (1). Further, in FIG. 1, M of PDTT_nCan be in the range of about 30kg mol^-1To about 35kg mol^-1Within the range of (1). Further, in FIG. 1, M of PDFT_nMay be in the range of about 35kg mol^-1To about 40kg mol^-1Within the range of (1). Furthermore, in FIG. 1, M of PBDTTPD_nMay be in the range of about 10kg mol^-1To about 35kg mol^-1Within the range of (1). Furthermore, in FIG. 1, M of PBDT-T8-TPD_nMay be in the range of about 35kg mol^-1To about 40kg mol^-1Within the range of (1). Furthermore, in FIG. 1, M of P3HT_nCan be in the range of about 50kg mol^-1To about 80kg mol^-1Within the range of (1). Finally, in FIG. 1, M of PBDT-T-FDP_nCan be in the range of about 50kg mol^-1To about 60kg mol^-1Within the range of (1).

Among the organic photodiodes suitable for 2D-sensitization areAnother material of the organic material is spiro-OMeTAD, which can provide both UV detection and hole transport properties (see Guo et al, J mater. chem.c,2018,6, 2573). As discussed above, an interlayer, such as but not limited to poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), can be used to improve the electrical connection to the bottom contact. Alternative suitable materials may include solution processable MoO₃Or V₂O_xInstead of PEDOT.

In some cases, the 2D QD-containing layer 230 includes about 10% to about 95% by volume 2D QDs and about 5% to about 90% by volume one or more charge transport materials. In some cases, 2D QD-containing layer 230 comprises about 20% to about 90%, alternatively about 30% to about 85%, alternatively about 40% to about 80%, alternatively about 50% to about 75%, and alternatively about 60% to about 70% by volume 2D QDs. In some cases, the 2D QD-containing layer 230 comprises from about 10% to about 80%, alternatively from about 15% to about 70%, alternatively from about 20% to about 60%, alternatively from about 25% to about 50%, and alternatively from about 30% to about 40%, by volume of one or more charge transport materials.

The thickness of the 2D QD-containing layer 230 may range from about 10nm to about 2 microns, alternatively from about 50nm to about 1 micron, and alternatively from about 100nm to about 750nm, and alternatively from about 200nm to about 500 nm.

Fig. 3 is a schematic diagram of a heterostructure photodetector 300 in accordance with aspects of the present disclosure. The heterostructure photodetector 300 includes a bottom electrode 310, and a first layer 320 having 2D nanoplatelets disposed on the bottom electrode 310, a second layer 330 having 2D QDs disposed on the first layer 320 containing 2D nanoplatelets, and a top electrode 340 disposed on the second layer 330 containing 2D QDs. In such a configuration, one or more of the top and bottom electrodes 310, 340 may be transparent to allow light to pass therethrough. To form the heterojunction, the 2D QDs and 2D nanoplates in layers 320, 330 are selected such that the conduction and valence bands of the 2D QDs are offset from the conduction and valence bands of the 2D nanoplates to form a built-in electric field. This can be achieved by: selecting 2D QD and 2D nanoplatelet materials having different semiconductor bandgaps, and/or adjusting the lateral dimensions of the second 2D QD and/or 2D nanoplatelet, and/or adjusting the thickness of the 2D QD and/or 2D nanoplatelet, and/or functionalizing the surface of one or both of the 2D QD and 2D nanoplatelet with different ligands that change the material bandgap. The junction width may control the wavelength of light absorbed.

The thickness of each of the 2D nanoplatelet containing layer 320 and the 2D QD containing layer 330 can independently range from about 10nm to about 1 micron, alternatively from about 25nm to about 750nm, alternatively from about 50nm to about 500nm, alternatively from about 75nm to about 400nm, and alternatively from about 100nm to about 300 nm. Preferably, the combined thickness of the 2D nanoplatelet containing layer 320 and the 2D QD containing layer 330 is from about 50nm to about 800nm, more preferably from about 100nm to about 700nm, and even more preferably from about 200nm to about 600 nm. In some cases, the 2D nanoplatelet containing layer 320 and the 2D QD containing layer 330 have the same or substantially the same thickness. In other cases, layer 330 containing 2D QDs is thicker than layer 320 containing 2D nanoplatelets. In other cases, layer 320 containing 2D nanoplatelets is thicker than layer 330 containing 2D QDs.

The 2D QD-containing layer 330 may be fabricated to have the same or substantially similar composition as the 2D QD-containing layer 230. As with the 2D QD-containing layer 230, the 2D nanoplatelet-containing layer 320 comprises from about 10% to about 95% by volume 2D nanoplatelets and from about 5% to about 90% by volume one or more charge transport materials. In some cases, the 2D nanoplatelet-containing layer 320 comprises from about 20% to about 90% by volume, alternatively from about 30% to about 85% by volume, alternatively from about 40% to about 80% by volume, alternatively from about 50% to about 75% by volume, and alternatively from about 60% to about 70% by volume 2D nanoplatelets. In some cases, the 2D nanoplatelet-containing layer 320 comprises from about 10 to about 80 volume percent, alternatively from about 15 to about 70 volume percent, alternatively from about 20 to about 60 volume percent, alternatively from about 25 to about 50 volume percent, and alternatively from about 30 to about 40 volume percent of the one or more charge transport materials.

In some cases, the heterostructure photodetector 300 can further include an intermediate layer (not shown) disposed between the bottom electrode 310 and the 2D nanoplate-containing layer 320. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. In fig. 3, the 2D nanoplatelet containing layer 320 and the 2D QD containing layer 330 are shown as separate layers. In some cases, a transition layer (not shown) having a combination of 2D nanoplatelets and 2D QDs may be disposed between 2D nanoplatelet-containing layer 320 and 2D QD-containing layer 330. In some cases, the relative amounts of the 2D nanoplatelets and the 2D QDs may be uniform or substantially uniform throughout the thickness of the transition layer. In some cases, the transition layer can exhibit a gradient in which the amount of 2D nanoplatelets is reduced from 2D nanoplatelet-containing layer 320 to 2D QD-containing layer 330. In some cases, the transition layer may exhibit a gradient in which the amount of 2D QDs increases from the 2D nanoplatelet containing layer 320 to the 2D QD containing layer 330.

Fig. 4 is a schematic diagram of another heterostructure photodetector 400 in accordance with aspects of the present disclosure. The heterostructure photodetector 400 includes a bottom electrode 410, and a first layer 420 having 2D QDs disposed on the bottom electrode 410, a second layer 430 having 2D QDs disposed on the first layer 420 containing 2D QDs, and a top electrode 440 disposed on the second layer 430 containing 2D QDs. In such a configuration, one or more of the top and bottom electrodes 410, 420 may be transparent to allow light to enter the device. To form the heterojunction, the 2D QDs of the first layer 420 and the 2D QDs of the second layer 430 are selected such that the conduction and valence bands of the 2D QDs in the first layer 420 are offset from the conduction and valence bands of the 2D QDs in the second layer 430. This can be achieved by: selecting the first and second 2D QDs of materials having different semiconductor bandgaps, and/or adjusting the lateral dimensions of the first and second 2D QDs, and/or adjusting the thickness of the first and second 2D QDs, and/or functionalizing the surface of one or both of the first and second 2D QDs with different ligands that change the material bandgaps. In some cases, the chemical composition of each of the first and second 2D QDs may be the same or substantially the same, but the first and second 2D QDs differ in one or more of lateral size, thickness, and surface functionalization. The junction width may control the wavelength of light absorbed.

The composition and/or thickness of each 2D QD-containing layer 420, 430 may be varied as described above for 2D QD-containing layer 230. Preferably, the combined thickness of the 2D QD-containing layers 420, 430 is from about 50nm to about 800nm, more preferably from about 100nm to about 700nm, and even more preferably from about 200nm to about 600 nm. In some cases, each 2D QD-containing layer 420, 430 has the same or substantially the same thickness. In other cases, layer 420 containing 2D QDs is thicker than layer 430 containing 2D QDs. In other cases, layer 430 containing 2D QDs is thicker than layer 420 containing 2D QDs.

In some cases, the heterostructure photodetector 400 can further include an intermediate layer (not shown) disposed between the bottom electrode 410 and the 2D QD-containing layer 420. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. In fig. 4, the 2D QD-containing layer 420 and the 2D QD-containing layer 430 are shown as separate layers. In some cases, a transition layer (not shown) having a combination of the first 2D QDs (i.e., the 2D QDs of layer 420) and the second 2D QDs (i.e., the 2D QDs of layer 430) may be disposed between the 2D QD-containing layer 420 and the 2D QD-containing layer 430. In some cases, the relative amounts of the first 2D QDs and the second 2D QDs may be uniform or substantially uniform throughout the thickness of the transition layer. In some cases, the transition layer may exhibit a gradient in which the amount of first 2D QDs is reduced from the 2D QD-containing layer 420 to the 2D QD-containing layer 430. In some cases, the transition layer may exhibit a gradient in which the amount of second 2D QDs increases from the 2D QD-containing layer 420 to the 2D QD-containing layer 430.

Fig. 5 is a schematic diagram of yet another heterostructure photodetector 500 in accordance with aspects of the present disclosure. The heterostructure photodetector 500 includes a bottom electrode 510, a first layer 520 having 2D QDs disposed on the bottom electrode 510, and a second layer 530 having conventional QDs disposed on the first layer 520 having 2D QDs, and a top electrode 540 disposed on the second layer 530 having conventional QDs. In such a configuration, one or more of the top and bottom electrodes 510, 540 may be transparent to allow light to enter the device. In order to form a heterojunction, the first 2D QD layer 520 and the second conventional QD layer 530 are selected such that the conduction band and the valence band of the first 2D QD layer are offset from the conduction band and the valence band of the second conventional QD layer. This can be achieved by: selecting conventional QDs and 2D QDs of materials having different semiconductor bandgaps, and/or adjusting the diameter of the conventional QDs, and/or adjusting the lateral dimensions of the 2D QDs, and/or adjusting the thickness of the 2D QDs, and/or functionalizing the surface of one or both of the 2D QDs and the conventional 2D QDs with different ligands that change the material bandgaps. The junction width may control the wavelength of light absorbed.

The 2D QD-containing layer 520 may be fabricated to have the same or substantially similar composition as the 2D QD-containing layer 230. As with the 2D QD-containing layer 230, the 2D nanoplatelet-containing layer 520 comprises from about 10% to about 95% by volume 2D nanoplatelets and from about 5% to about 90% by volume one or more charge transport materials. In some cases, the conventional QD-containing layer 530 comprises about 20% to about 90%, alternatively about 30% to about 85%, alternatively about 40% to about 80%, alternatively about 50% to about 75%, and alternatively about 60% to about 70% by volume of conventional QDs. In some cases, the conventional QD-containing layer 530 includes from about 10% to about 80%, alternatively from about 15% to about 70%, alternatively from about 20% to about 60%, alternatively from about 25% to about 50%, and alternatively from about 30% to about 40% by volume of one or more charge transport materials.

In some cases, the heterostructure photodetector 500 can further include an intermediate layer (not shown) disposed between the bottom electrode 510 and the 2D QD-containing layer 520. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. In fig. 5, the 2D QD-containing layer 520 and the conventional QD-containing layer 530 are shown as separate layers. In some cases, a transition layer (not shown) having a combination of 2D QDs (i.e., the 2D QDs of layer 520) and conventional QDs (i.e., the conventional QDs of layer 530) may be disposed between 2D QD-containing layer 520 and conventional QD-containing layer 530. In some cases, the relative amounts of 2D QDs and conventional QDs may be uniform or substantially uniform throughout the thickness of the transition layer. In some cases, the transition layer may exhibit a gradient in which the amount of 2D QDs is reduced from the 2D QD-containing layer 520 to the conventional QD-containing layer 530. In some cases, the transition layer may exhibit a gradient in which the amount of conventional QDs increases from the 2D QD-containing layer 520 to the conventional QD-containing layer 530.

Fig. 6 is a schematic diagram of yet another heterostructure photodetector 600 in accordance with aspects of the present disclosure. The heterostructure photodetector 600 includes a bottom electrode 610, a first layer 620 having conventional QDs disposed on the bottom electrode 610, and a second layer 630 having 2D QDs disposed on the first layer 620 having conventional QDs, and a top electrode 640 disposed on the second layer 630 having 2D QDs. In such a configuration, one or more of the top and bottom electrodes 610, 640 may be transparent to allow light to enter the device. To form a heterojunction, the first layer 620 containing the conventional QDs and the second layer 630 containing the 2D QDs are selected such that the conduction and valence bands of the conventional QDs are offset from the conduction and valence bands of the 2D QDs. This can be achieved by: selecting conventional QDs and 2D QDs of materials having different semiconductor bandgaps, and/or adjusting the diameter of the conventional QDs, and/or adjusting the lateral dimensions of the 2D QDs, and/or adjusting the thickness of the 2D QDs, and/or functionalizing the surface of one or both of the 2D QDs and the conventional 2D QDs with different ligands that change the material bandgaps. The junction width may control the wavelength of light absorbed.

The composition and/or thickness of the conventional QD-containing layer 620 and the 2D QD-containing layer 630 may be varied as described above for the conventional QD-containing layer 520 and the 2D QD-containing layer 520, respectively. Preferably, the combined thickness of the conventional QD-containing layer 620 and the 2D QD-containing layer 630 is from about 50nm to about 800nm, more preferably from about 100nm to about 700nm, and even more preferably from about 200nm to about 600 nm. In some cases, each of the conventional QD-containing layer 620 and the 2D QD-containing layer 630 has the same or substantially the same thickness. In other cases, QD-containing layer 620 is thicker than 2D QD-containing layer 630. In other cases, layer 630 containing 2D QDs is thicker than layer 620 containing QDs.

In some cases, the heterostructure photodetector 600 may further include an intermediate layer (not shown) disposed between the bottom electrode 610 and the conventional QD-containing layer 620. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. In fig. 6, the layer 620 containing conventional QDs and the layer 630 containing 2D QDs are shown as separate layers. In some cases, a transition layer (not shown) having a combination of conventional QDs (i.e., the conventional QDs of layer 620) and 2D QDs (i.e., the 2D QDs of layer 630) may be disposed between conventional QD-containing layer 620 and 2D QD-containing layer 630. In some cases, the relative amounts of conventional QDs and 2D QDs may be uniform or substantially uniform throughout the thickness of the transition layer. In some cases, the transition layer may exhibit a gradient in which the amount of conventional QDs is reduced from the conventional QD-containing layer 620 to the 2D QD-containing layer 630. In some cases, the transition layer may exhibit a gradient in which the amount of 2D QDs increases from the conventional QD-containing layer 620 to the 2D QD-containing layer 630.

Fig. 7 is a schematic diagram of a heterostructure photodetector 700 in accordance with aspects of the present disclosure. The heterostructure photodetector 700 includes a bottom electrode 710, and a first layer 720 of 2D QDs disposed on the bottom electrode 710, a second layer 730 of 2D nanoplatelets disposed on the first layer 720 containing 2D QDs, and a top electrode 740 disposed on the second layer 730 containing 2D nanoplatelets. In such a configuration, one or more of the top and bottom electrodes 710, 740 may be transparent to allow light to enter the device. To form the heterojunction, the 2D QDs and 2D nanoplates in layers 720, 730 are further processed such that the conduction and valence bands of the 2D QDs are offset from the conduction and valence bands of the 2D nanoplates to form a built-in electric field. This can be achieved by: selecting 2D QD and 2D nanoplatelet materials having different semiconductor bandgaps, and/or adjusting the lateral dimensions of the second 2D QD and/or 2D nanoplatelet, and/or adjusting the thickness of the 2D QD and/or 2D nanoplatelet, and/or functionalizing the surface of one or both of the 2D QD and 2D nanoplatelet with different ligands that change the material bandgap. The junction width may control the wavelength of light absorbed.

The composition and/or thickness of the 2D QD-containing layer 720 and the 2D nanoplatelet-containing layer 730 can be varied as described above for the 2D QD-containing layer 330 and the 2D nanoplatelet-containing layer 320, respectively. Preferably, the combined thickness of the 2D QD-containing layer 720 and the 2D nanoplatelet-containing layer 730 is from about 50nm to about 800nm, more preferably from about 100nm to about 700nm, and even more preferably from about 200nm to about 600 nm. In some cases, each of the 2D QD-containing layer 720 and the 2D nanoplatelet-containing layer 730 has the same or substantially the same thickness. In other cases, the layer 720 containing 2D QDs is thicker than the layer 730 containing 2D nanoplatelets. In other cases, the layer 730 containing 2D nanoplatelets is thicker than the layer 720 containing 2D QDs.

In some cases, the heterostructure photodetector 700 can further include an intermediate layer (not shown) disposed between the bottom electrode 710 and the 2D QD-containing layer 720. The intermediate layer may be made of the same material as the intermediate layer 220 of the photodetector 200. In fig. 7, the 2D QD-containing layer 720 and the 2D nanosheet-containing layer 730 are shown as separate layers. In some cases, a transition layer (not shown) having a combination of 2D QDs (i.e., the 2D QDs of layer 720) and 2D nanoplatelets (i.e., the 2D nanoplatelets of layer 730) may be disposed between 2D QD-containing layer 720 and 2D nanoplatelet-containing layer 730. In some cases, the relative amounts of the 2D QDs and the 2D nanoplatelets may be uniform or substantially uniform throughout the thickness of the transition layer. In some cases, the transition layer may exhibit a gradient in which the amount of 2D QDs is reduced from the 2D QD-containing layer 720 to the 2D nanosheet-containing layer 730. In some cases, the transition layer may exhibit a gradient in which the amount of 2D nanoplatelets increases from the 2D QD-containing layer 720 to the 2D nanoplatelet-containing layer 730.

2D QDs according to aspects of the present disclosure may be colloidally synthesized and deposited via solution processing. Suitable 2D QD materials include, but are not limited to:

graphene, graphene oxide and reduced graphene oxide;

TMDC, e.g. WO₂；WS₂；WSe₂；WTe₂；MnO₂；MoO₂；MoS₂；MoSe₂；MoTe₂；NiO₂；NiTe₂；NiSe₂；VO₂；VS₂；VSe₂；TaS₂；TaSe₂；RuO₂；RhTe₂；PdTe₂；HfS₂；NbS₂；NbSe₂；NbTe₂；FeS₂；TiO₂；TiS₂；TiSe₂(ii) a And ZrS₂；

Transition metal trisulfides, e.g. TaO₃；MnO₃；WO₃；ZrS₃；ZrSe₃；HfS₃(ii) a And HfSe₃；

Group 13-16(III-VI) compounds, such as, for example, InS; InSe; GaS; GaSe; and GaTe;

compounds of groups 15-16(IV-VI), such as, for example, Bi₂Se₃(ii) a And B_i2Te₃；

Nitrides, such as for example h-BN;

oxides, such as, for example, LaVO₃；LaMnO₃；V₂O₅；LaNbO₇；Ca₂Nb₃O₁₀；Ni(OH)₂(ii) a And Eu (OH)₂(ii) a A layered copper oxide; mica; and Bismuth Strontium Calcium Copper Oxide (BSCCO);

phosphides, e.g. Li₇MnP₄(ii) a And MnP₄(ii) a And

2D allotropes of group 14 elements, such as, for example, silylene (silicone); germenene (germanene); and stannene (stanene).

In the foregoing materials, adjacent layers are held together by van der waals interactions, which can be easily broken by techniques such as lift-off techniques (e.g., liquid phase lift-off (LPE)) to form 2D flakes. In alternative embodiments, the 2D QDs may comprise traditionally non-layered semiconductor materials, including but not limited to:

group 12-16(II-VI) semiconductors such as, for example, ZnS; ZnSe; CdS; CdSe; CdTe;

group 13-15(III-V) materials such as, for example, AlN, AlP, AlAs, GaN; GaP; GaAs; InN; InP; InAs;

group 15-16(V-VI) materials, such as, for example, PbS, PbSe, PbTe; and

group I-III-VI materials, such as CuGaS₂；CuGaSe₂；CuGa(S,Se)₂；CuInS₂、CuInSe₂；CuIn(S,Se)₂；Cu(In,Ga)S₂；Cu(In,Ga)Se₂；Cu(In,Ga)(S,Se)₂；CuInTe₂；AgInS₂(ii) a And AgInSe₂Including their dopants and alloys.

For example, 2D QDs of the foregoing materials may be formed via physical or chemical cleavage methods. Specifically, zero-dimensional (0D), one-dimensional (1D), or three-dimensional (3D) of desired shape, size, and composition may be formed followed by treatments such as chemical treatments, e.g., reflow, LPE, and reflow or intercalation and exfoliation, to form 2D QDs of uniform size according to the intrinsic shape of the 3D or OD nanoparticles. The method is scalable and can be used for mass production of 2D QDs with uniformity. As used herein, "cleavage" of a nanoparticle means the separation of the nanoparticle into two or more portions. The term is not intended to imply any limitation on the method of separation and may include physical and chemical methods of separation. Physical separation methods may include, but are not limited to: mechanical stripping (so-called "Scotch tape process"), delamination, grinding and kneading. As used herein, "chemical cleavage" of a nanoparticle means the separation of the nanoparticle into two or more portions, wherein the separation is achieved by chemical treatment. In certain embodiments, the chemical treatment may comprise: applying heat, pressure, vacuum, ultrasound and/or agitation to the solution or dispersion of nanoparticles; chemical etching; and intercalation. Non-limiting examples of chemical cleavage methods include: refluxing the nanoparticles in solution; LPE of nanoparticles and subsequent refluxing; or intercalation and exfoliation of nanoparticles.

The cleavage of 0D, 1D, or 3D nanoparticles into 2D QDs may be performed using any suitable technique. Suitable examples include chemical and physical stripping methods. In one embodiment, the cleavage of the preformed nanoparticles is performed by a chemical method such as LPE, which comprises sonicating the preformed nanoparticles in a solvent. The surface tension of the solvent may be selected to match the material being stripped. In some embodiments, the delaminated nanoparticles are then refluxed in a solution.

In some embodiments, cleavage of 0D, 1D, or 3D nanoparticles can be performed by refluxing the preformed nanoparticles in solution without prior exfoliation. One of ordinary skill in the art will recognize that the reflux temperature of the 0D, 1D, or 3D nanoparticle solution will depend on the boiling point of the solvent in which the solution is formed. Without wishing to be bound by any particular theory, one possible mechanism is that the application of heat may thermally expand the layers within the 0D, 1D, or 3D nanoparticles; refluxing the solution can form a gas that chemically cleaves the layers apart. In some embodiments, the solution includes a coordinating solvent. Examples of suitable coordinating solvents include, but are not limited to: saturated alkylamines, e.g. C₆-C₅₀An alkylamine; unsaturated fatty amines, such as, for example, oleylamine; fatty acids such as, for example, myristic acid, palmitic acid and oleic acid; phosphines, such as for example Trioctylphosphine (TOP); phosphine oxides such as, for example, trioctylphosphine oxide (TOPO); alcohols, such as, for example, cetyl alcohol, benzyl alcohol, ethylene glycol, propylene glycol; and may include primary, secondary, tertiary, and branched solvents. In some embodiments, the solution includes a non-coordinating solvent, such as, but not limited to, C₁₁-C₅₀An alkane. In some embodiments, the boiling point of the solvent is from 150 ℃ to 600 ℃, such as from 160 ℃ to 400 ℃, or more particularly from 180 ℃ to 360 ℃. In a particular embodiment, the solvent is hexadecylamine.

In other embodiments, the cutting of the preformed nanoparticles is performed by intercalation and exfoliation methods. Intercalation and exfoliation of TMDC multilayer nanostructures can be accomplished using lewis base intercalation methods. The first intercalation and exfoliation process may be carried out by: the preformed nanoparticles are stirred in the first solvent in the presence of the first intercalant and the second intercalant for a first period of time. Optionally, a second solvent may be subsequently added followed by stirring for a second period of time. In some embodiments, the second intercalation and exfoliation process occurs by: the product of the first intercalation and exfoliation process is mixed with a third intercalating agent and a third solvent and stirred for a third period of time. Optionally, a fourth solvent may be subsequently added followed by stirring for a fourth period of time. The first and second intercalants may include a hydrocarbon compound, wherein the hydrocarbon chain length of the first intercalant is different from the hydrocarbon chain length of the second intercalant. The third intercalant may be the same or different from the first and/or second intercalants. Suitable first, second, and third intercalants may include, but are not limited to:

lewis bases, such as amines, such as for example propylamine, hexylamine; alkoxides, such as, for example, sodium methoxide, sodium ethoxide; carboxylates, such as for example sodium caproate; and aminoalcohols, such as, for example, 3-amino-1-propanol;

aminothiols, such as, for example, mercaptoethylamine, 6-amino-1-hexanethiol and 8-amino-1-octanethiol;

amino acids, including alkyl amino acids, such as, for example, 3-aminopropionic acid (. beta. -alanine), 6-aminocaproic acid, 8-aminocaprylic acid; and

metal salts, such as, for example, those having the formula MX_nWherein M is Mo, Cd, Zn or In, and X is a halide (especially Cl)^-、Br^-And I^-) Acetate, octanoate, palmitate, laurate, myristate or oleate. Another suitable metal salt is [ MoCl ]₅]₂。

In general, the choice of the solvent or solvents in which the intercalation and exfoliation processes are carried out will depend on the choice of nanoparticles and intercalant. During intercalation and exfoliation, it is desirable that the nanoparticles be well dispersed or dissolved in one or more solvents. It is also desirable that the one or more intercalants be soluble in the one or more solvents. The second solvent may be different from the first solvent. The third solvent may be the same as the first solvent or the second solvent, or may be different from both the first solvent and the second solvent. In some cases, suitable solvents include polar aprotic solvents, such as, for example, dimethyl sulfoxide (DMSO), N-methylformamide (NMF), and acetonitrile. In some cases, suitable solvents include polar protic solvents, such as, for example, propanol and isopropanol.

The first time period may range from about 1 hour to about 1 month, alternatively from about 2 hours to about 2 weeks, and alternatively from about 4 hours to about 3 days. The second time period may range from about 1 hour to about 2 months, alternatively from about 2 days to about 2 weeks, and alternatively from about 1 week to about 3 weeks. The third time period may range from about 1 hour to about 1 month, alternatively from about 2 hours to about 2 weeks, and alternatively from about 4 hours to about 3 days. The fourth time period may range from about 1 hour to about 2 months, alternatively from about 2 days to about 2 weeks, and alternatively from about 1 week to about 3 weeks. In general, the time period will depend on factors such as: the choice of solvent or solvents and intercalating agent or agents, the strength of the bonding within the nanoparticles, and the concentration of nanoparticles in the solvent relative to the intercalating agent, and a higher yield of 2D nano-platelets can be obtained over a longer period of time.

In some embodiments, the first and/or second and/or subsequent intercalation and exfoliation processes may be achieved using sonication. Using sonication instead of agitation can help shorten the time period or time periods required to achieve the chemical cutting process.

Other cleavage techniques may be used to cleave 0D, 1D, or 3D nanoparticles into 2D QDs, such as, but not limited to, etching techniques. According to particular embodiments, the 2D QDs may then be purified by methods such as, but not limited to, centrifugation; filtering; dialysis or column chromatography techniques. The resulting 2D nanoplatelets can be dispersed in a solvent to form an ink, which can be deposited using conventional solution-based deposition techniques to form thin films, such as, but not limited to: drop casting, spin coating, slot coating, spray coating, slot dye coating, ink jet printing, or blade coating. Inherent uniformity in the properties of 2D QDs can result in a resulting film with a high degree of uniformity. The film thickness can be controlled by, for example, varying the concentration of the ink and/or by varying the size of the 2D QDs.

The layer of 2D nanoplatelets may be formed using techniques such as, but not limited to: mechanical stripping, Chemical Vapor Deposition (CVD), Atomic Layer Deposition (ALD); molecular Beam Epitaxy (MBE); lateral heteroepitaxy (lateral heteroepitaxy); and gas-solid growth. Suitable 2D nanoplatelets for the 2D nanoplatelet containing layer include, but are not limited to:

graphene, graphene oxide and reduced graphene oxide;

TMDC, e.g. WO₂；WS₂；WSe₂；WTe₂；MnO₂；MoO₂；MoS₂；MoSe₂；MoTe₂；NiO₂；NiTe₂；NiSe₂；VO₂；VS₂；VSe₂；TaS₂；TaSe₂；RuO₂；RhTe₂；PdTe₂；HfS₂；NbS₂；NbSe₂；NbTe₂；FeS₂；TiO₂；TiS₂；TiSe₂(ii) a And ZrS₂；

Transition metal trisulfides, e.g. TaO₃；MnO₃；WO₃；ZrS₃；ZrSe₃；HfS₃(ii) a And HfSe₃；

Group 13-16(III-VI) compounds, such as, for example, InS; InSe; GaS; GaSe; and GaTe;

compounds of groups 15-16(IV-VI), such as, for example, Bi₂Se₃(ii) a And Bi₂Te₃；

Nitrides, such as for example h-BN;

oxides, such as, for example, LaVO₃；LaMnO₃；V₂O₅；LaNbO₇；Ca₂Nb₃O₁₀；Ni(OH)₂(ii) a And Eu (OH)₂(ii) a A layered copper oxide; mica; and BSCCO;

phosphides, e.g. Li₇MnP₄(ii) a And MnP₄(ii) a And

2D allotropes of group 14 elements, such as, for example, silylene; a germanium ene; and stannenes.

For devices containing conventional QD-containing layers, the QD layer may be formed from materials including, but not limited to:

IIA-VIB (2-16) material consisting of a first element from group 2 of the periodic Table and a second element from group 16 of the periodic Table, and further including ternary and quaternary materials and dopant materials. Nanoparticle materials include, but are not limited to: MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe;

IIB-VIB (12-16) materials consisting of a first element from group 12 of the periodic Table and a second element from group 16 of the periodic Table, and also ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe;

II-V materials consisting of a first element from group 12 of the periodic Table and a second element from group 15 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: zn₃P₂、Zn₃As₂、Cd₃P₂、Cd₃As₂、Cd₃N₂、Zn₃N₂；

III-V materials consisting of a first element from group 13 of the periodic Table and a second element from group 15 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: BP, AlP, AlAs, AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, AlN, BN;

III-IV materials, which consist of a first element from group 13 of the periodic Table and a second element from group 14 of the periodic Table, and also include ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: b is₄C、Al₄C₃、Ga₄C；

III-VI materials consisting of a first element from group 13 of the periodic Table and a second element from group 16 of the periodic Table, and also including ternary and quaternary materials. Nanoparticle materials include, but are not limited to: al (Al)₂S₃、Al₂Se₃、Al₂Te₃、Ga₂S₃、Ga₂Se₃、GeTe；In₂S₃、In₂Se₃、Ga₂Te₃、In₂Te₃、InTe；

IV-VI materials consisting of a first element from group 14 of the periodic Table and a second element from group 16 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: PbS, PbSe, PbTe, SnS, SnSe, SnTe;

V-VI materials consisting of a first element from group 15 of the periodic Table and a second element from group 16 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: bi₂Te₃、Bi₂Se₃、Sb₂Se₃、Sb₂Te₃(ii) a And

nanoparticle materials consisting of a first element from any one of the transition metals of the periodic table and a second element from group 16 of the periodic table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: NiS, CrS, CuInS₂、AgInS₂。

In some cases, in a heterostructure device according to aspects of the present disclosure, the relative band gaps of the semiconductor materials can be selected to form a type I heterostructure, e.g., with MoTe₂2D QD layer or MoTe₂WSe of 2D nanosheet layer₂2D QDs. In some cases, the relative band gaps of the semiconductor materials may be selected to form a type II heterostructure, e.g., with WSe₂PbS QDs of 2D QD layer, or with WSe₂2D QD layer or WSe₂MoS of nanosheets₂ 2D QD。

In some cases, the thickness of one or more of the 2D layers may be a single monolayer. Making the sensitizer as thin as possible may be advantageous to maximize charge shielding effectiveness, flexibility, and device transparency. A thickness near the absorption depth may be desirable to maximize absorption of incident light. However, for stronger absorption, thicker devices may also be required. Adjusting the thickness of the material also provides a means to control its band gap. Thus, in some cases, one or more of the 2D layers may be 1-5 monolayers. In some cases, the 2D nanosheet may be a monolayer. A single layer may provide advantageous properties compared to several layers or bulk materials. For example, transition metal dichalcogenides exhibit a transition from an indirect bandgap to a direct bandgap upon monolayer formation.

Various strategies may be implemented to enhance charge transport within the 2D QD layer. For example, the intrinsic 2D QD ligands may be replaced with shorter chain ligands. As used herein, "short-chain ligand" refers to a ligand having a hydrocarbon chain of eight carbons or less. Suitable short chain ligands include, but are not limited to: alkanethiols such as 1-octanethiol, 1-heptanethiol, 1-hexanethiol, 1-pentanethiol, 1-butanethiol, 1-propanethiol; alkylamines, such as methylamine, ethylamine, propylamine, butylamine, octylamine, allylamine; and carboxylic acids such as octanoic acid, heptanoic acid, hexanoic acid, pentanoic acid, butanoic acid, and propanoic acid. Other suitable ligands may include pyridine and pyrrolidone. In some cases, bridging ligands may be used to improve connectivity between adjacent 2D QDs. Suitable examples include, but are not limited to, bidentate ligands such as ethanedithiol or 3-mercaptopropionic acid.

Another strategy to improve connectivity between 2D QDs may include the use of chalcogen ligands. In this approach, QDs can be "necked" by removing the organic surface ligands and passivating the QD surface with chalcogen ligands. In some cases, adjacent QDs may fuse. Films may be formed using fused 2D QDs, where the 2D QDs include ligands on unfused portions of their outer surfaces. The fusion may result in the 2D QDs substantially maintaining their respective properties while being connected via a region through which current can easily flow. In one embodiment, 2D QDs that have been synthesized may undergo ligand exchange to replace the intrinsic ligands with shorter, more volatile ligands. The ligand-exchanged 2D QDs may then be solution deposited, and then the short chain ligands removed to bring the 2D QDs into close proximity, so that some of the 2D QDs are in contact with their neighbors. This is called "necking". Subsequently, the necked 2D QDs may be annealed to fuse the 2D QDs together. In general, fused 2D QDs and the connections between them will not contain defect states, which makes current flow easily between them.

When conventional QDs are used (e.g., in conventional QD-containing layer 530 of photodetector 500 or conventional QD-containing layer 620 of photodetector 600), the conventional QDs may be core, core-shell, or core-multishell QDs having a size in the range of 2-100 nm. The material of the core may include:

IIA-VIA (2-16) materials consisting of a first element from group 2 of the periodic Table and a second element from group 16 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe;

IIB-VIA (12-16) materials, which consist of a first element from group 12 of the periodic Table and a second element from group 16 of the periodic Table, and also include ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe;

II-V materials consisting of a first element from group 12 of the periodic Table and a second element from group 15 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: zn₃P₂、Zn₃As₂、Cd₃P₂、Cd₃As₂、Cd₃N₂、Zn₃N₂；

III-V materials consisting of a first element from group 13 of the periodic Table and a second element from group 15 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: BP, AlP, AlAs, AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, AlN, BN;

III-IV materials consisting of a first element from group 13 of the periodic Table and a second element from group 14 of the periodic Table and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: b is₄C、A1₄C₃、Ga₄C；

III-VI materials consisting of a first element from group 13 of the periodic Table and a second element from group 16 of the periodic Table, and also including ternary and quaternary materials. Nanoparticle materials include, but are not limited to: al (Al)₂S₃、Al₂Se₃、Al₂Te₃、Ga₂S₃、Ga₂Se₃、GeTe；In₂S₃、In₂Se₃、Ga₂Te₃、In₂Te₃、InTe；

IV-VI materials consisting of a first element from group 14 of the periodic Table and a second element from group 16 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: PbS, PbSe, PbTe, SnS, SnSe, SnTe;

V-VI materials consisting of a first element from group 15 of the periodic Table and a second element from group 16 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: bi₂Te₃、Bi₂Se₃、Sb₂Se₃、Sb₂Te₃(ii) a And

nanoparticle materials consisting of a first element from any one of the transition metals of the periodic table and a second element from group 16 of the periodic table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: NiS, CrS, CuInS₂、AgInS₂。

For the purposes of the specification and claims, the term doped nanoparticle refers to the above-described nanoparticles and dopants consisting of one or more main group or rare earth elements, most commonly transition metals or rare earth elements such as, but not limited to, zinc sulfide with manganese, such as doped with Mn⁺ZnS nanoparticles of (1).

For the purposes of the specification and claims, the term "ternary material" refers to the QDs described above, but which are ternary materials. The three components are generally a combination of elements from the above groups, an example being (Zn)_xCd_x-1S)_mL_nNanocrystals (where L is a capping agent).

For the purposes of the specification and claims, the term "quaternary material" refers to the nanoparticles described above, but which are four-component materials. The four components are generally elements from the above groupCompositions of elements, examples being (Zn)_xCd_x-1S_ySe_y-l)_mL_nNanocrystals (where L is a capping agent).

In most cases, the material used for any shell or subsequent number of shells grown on a conventional QD core will have a similar lattice type material to that of the core material, i.e. a high lattice match to the core material so that it can be grown epitaxially on the core, but need not be limited to such compatible materials. In most cases, the material used for any shell or subsequent number of shells grown on the core present will have a wider band gap than the core material, but need not be limited to such compatible materials. The material of any shell or subsequent number of shells grown on the core includes materials including:

IIA-VIA (2-16) materials consisting of a first element from group 2 of the periodic Table and a second element from group 16 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe;

IIB-VIA (12-16) materials, which consist of a first element from group 12 of the periodic Table and a second element from group 16 of the periodic Table, and also include ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe;

II-V materials consisting of a first element from group 12 of the periodic Table and a second element from group 15 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: zn₃P₂、Zn₃As₂、Cd₃P₂、Cd₃As₂、Cd₃N₂、Zn₃N₂；

III-V materials consisting of a first element from group 13 of the periodic Table and a second element from group 15 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: BP, AlP, AlAs, AlSb; GaN, GaP, GaAs, GaSb; InN, InP, InAs, InSb, AlN, BN;

III-IV materials, which consist of a first element from group 13 of the periodic Table and a second element from group 14 of the periodic Table, and also include ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: b is₄C、A1₄C₃、Ga₄C；

III-VI materials consisting of a first element from group 13 of the periodic Table and a second element from group 16 of the periodic Table, and also including ternary and quaternary materials. Nanoparticle materials include, but are not limited to: al (Al)₂S₃、Al₂Se₃、Al₂Te₃、Ga₂S₃、Ga₂Se₃、In₂S₃、In₂Se₃、Ga₂Te₃、In₂Te₃；

IV-VI materials consisting of a first element from group 14 of the periodic Table and a second element from group 16 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: PbS, PbSe, PbTe, SnS, SnSe, SnTe;

V-VI materials consisting of a first element from group 15 of the periodic Table and a second element from group 16 of the periodic Table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: bi₂Te₃、Bi₂Se₃、Sb₂Se₃、Sb₂Te₃(ii) a And

nanoparticle materials consisting of a first element from any one of the transition metals of the periodic table and a second element from group 16 of the periodic table, and further including ternary and quaternary materials and doped materials. Nanoparticle materials include, but are not limited to: NiS, CrS, CuInS₂、AgInS₂。

The aforementioned strategies for increasing connectivity within the 2D QD layer may also be applied to conventional QD layers.

Photodetector devices according to aspects of the present disclosure may be integrated with complementary metal-oxide-semiconductor (CMOS) circuitry. Devices comprising 2D QDs may be fabricated using CMOS technology, for example by spin coating a 2D QD layer onto a pre-fabricated CMOS electronic readout circuit. Integration into CMOS circuitry may be desirable to form small pixels to enable high resolution sensors.

In some cases, multiple pixels with spectral sensitivity in different regions may be monolithically integrated. The spectral sensitivity of each pixel can be tuned by varying the lateral dimensions and/or thickness of the 2D QDs.

In some cases, a phototransistor device according to aspects of the present disclosure may be gated. Gating acts as a control mechanism and allows increased functionality, as the gate voltage can be varied to act as a switch or amplifier. In particular, the high carrier mobility of 2D materials may be advantageous because the gain is directly proportional to the carrier mobility.

The foregoing represents a specific embodiment which embodies the principles of the present invention. Those skilled in the art will be able to devise alternatives and modifications which, even if not explicitly disclosed herein, embody those principles and are thus within the scope of the invention. While particular embodiments of the present invention have been illustrated and described, they are not intended to limit what is covered by this patent. It will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as literally and equivalently covered by the appended claims.