阅读说明：本技术 一种具有锗梯度的铜锌锡锗硒吸收层薄膜的制备方法 (Preparation method of copper-zinc-tin-germanium-selenium absorption layer film with germanium gradient ) 是由 王书荣 杨帅 徐信 李新毓 李祥 王亭保 于 2020-06-24 设计创作，主要内容包括：本发明公开了一种具有锗梯度的铜锌锡锗硒吸收层薄膜的制备方法,具体包括以下步骤：(1)衬底预处理；(2)钼层和锗层的制备：在预处理后的所述衬底上依次沉积第一钼层、锗层、第二钼层；(3)铜锌锡硫预制层的制备；(4)铜锌锡锗硒吸收层薄膜的制备：将步骤(3)铜锌锡硫预制层制备完成后的所述衬底在210℃热处理30min,然后与硒粉放入硒化炉中,以20℃/min的升温速率从室温升温至550℃,并保温10～13min,自然冷却至室温后得到具有锗梯度的铜锌锡锗硒吸收层薄膜；通过本发明的制备方法可以在背表面形成Ge的浓度梯度,形成一个电子的阻挡层,阻挡载流子在背表面界面处的复合,提高铜锌锡硒基薄膜的载流子收集效率,进一步提升薄膜的性能。(The invention discloses a preparation method of a copper-zinc-tin-germanium-selenium absorption layer film with a germanium gradient, which specifically comprises the following steps: (1) preprocessing a substrate; (2) preparation of molybdenum and germanium layers: depositing a first molybdenum layer, a germanium layer and a second molybdenum layer on the pretreated substrate in sequence; (3) preparing a copper-zinc-tin-sulfur prefabricated layer; (4) preparing a copper-zinc-tin-germanium-selenium absorption layer film: carrying out heat treatment on the substrate after the copper-zinc-tin-sulfur prefabricated layer in the step (3) is prepared at 210 ℃ for 30min, then putting the substrate and selenium powder into a selenizing furnace, heating the substrate from room temperature to 550 ℃ at the heating rate of 20 ℃/min, preserving the heat for 10-13min, and naturally cooling the substrate to room temperature to obtain a copper-zinc-tin-germanium-selenium absorption layer film with a germanium gradient; by the preparation method, the Ge concentration gradient can be formed on the back surface to form an electronic barrier layer to prevent the combination of current carriers at the interface of the back surface, so that the current carrier collection efficiency of the copper-zinc-tin-selenium-based film is improved, and the performance of the film is further improved.)

1. A preparation method of a copper-zinc-tin-germanium-selenium absorption layer film with a germanium gradient is characterized by comprising the following steps:

(1) substrate pretreatment: cleaning and soaking the substrate, and blow-drying for later use;

(2) preparation of molybdenum and germanium layers: depositing a first molybdenum layer, a germanium layer and a second molybdenum layer on the pretreated substrate in sequence;

(3) preparing a copper-zinc-tin-sulfur prefabricated layer: depositing the ZnS layer, the CuS layer, the Sn layer and the CuS layer on the second molybdenum layer in sequence to obtain a copper-zinc-tin-sulfur prefabricated layer;

(4) preparing a copper-zinc-tin-germanium-selenium absorption layer film: and (3) carrying out heat treatment on the substrate after the copper-zinc-tin-sulfur prefabricated layer is prepared at 210 ℃ for 30min, then putting the substrate and selenium powder into a selenizing furnace, heating the substrate and selenium powder from room temperature to 550 ℃ at a heating rate of 20 ℃/min, preserving the heat for 10-13min, and naturally cooling the substrate to room temperature to obtain the copper-zinc-tin-germanium-selenium absorption layer film with germanium gradient.

2. The method for preparing the Cu-Zn-Sn-Ge-Se absorption layer film with the Ge gradient according to claim 1, wherein the substrate is a soda-lime glass substrate.

3. The method for preparing a cu-zn-sn-ge-se absorption layer film with a ge gradient according to claim 1, wherein the step of cleaning and soaking in the step (1) is: sequentially cleaning the substrate with cleaning powder and washing powder, then ultrasonically cleaning the substrate with acetone and alcohol, then soaking the substrate in a potassium dichromate solution for 8-10h, and finally ultrasonically cleaning with deionized water.

4. The method for preparing the copper-zinc-tin-germanium-selenium absorption layer film with the germanium gradient according to claim 3, wherein the ultrasonic cleaning time is 30min, and the concentration of the potassium dichromate solution is 0.4 mol/L.

5. The method for preparing a Cu-Zn-Sn-Ge-Se absorption layer film with Ge gradient as claimed in claim 1, wherein in step (2), the thickness of the first Mo layer is 0.8 μm, and the thickness of the second Mo layer is 0.3 μm.

6. The method for preparing the Cu-Zn-Sn-Ge-Se absorption layer film with the Ge gradient according to claim 1, wherein the sputtering power of the Ge layer in the step (2) is 25W, and the deposition time is 20 min.

7. The method for preparing a Cu-Zn-Sn-Ge-Se absorption layer film with a Ge gradient as claimed in claim 1, wherein the deposition in step (3) is a periodic step-by-step sputtering deposition, and the period is 3.

8. The method for preparing the Cu-Zn-Sn-Ge-Se absorption layer film with the Ge gradient according to claim 7, wherein each period comprises the following specific steps: and respectively carrying out sputtering deposition on the target material on the second molybdenum layer according to the sequence of ZnS, CuS, Sn and CuS, wherein the sputtering power of each target material is 50W, and the sputtering time is 48min, 41min, 14min and 41min in sequence.

9. The method for preparing a Cu-Zn-Sn-Ge-Se absorption layer film with Ge gradient as claimed in claim 1, wherein the thickness of the Cu-Zn-Sn-S pre-fabricated layer in step (3) is 1.2 μm.

10. The method for preparing a Cu-Zn-ge-se absorption layer film with ge gradient according to claim 1, wherein the molar relationship of Cu, Zn and Sn in the Cu-Zn-Sn-s prefabricated layer in step (3) satisfies the relationship of Cu/Zn + Sn being 0.65 and Zn/Sn being 1.

Technical Field

The invention relates to the technical field of new energy of photoelectric materials, in particular to a preparation method of a copper-zinc-tin-germanium-selenium absorption layer film with a germanium gradient.

Background

In the last decades of solar cell research and development, the first generation silicon solar cell development has gradually entered the saturation phase, so researchers are turning to new material, new type solar cell with higher conversion efficiency and lower cost, i.e. the second generation solar cell: thin film solar cells, such as single-junction Cu (In, Ga) Se₂(CIGS), CdTe, and GaAs, which have developed rapidly in subsequent studies and achieved significant success. However, the substances used In these thin film materials include toxic heavy metal cadmium (Cd) and rare metals tellurium (Te), indium (In), gallium (Ga), etc., which limit their mass production and application and future development prospects, compared with high-efficiency CIGS thin film cells, Cu is used for Cu₂ZnSnSe₄The (CZTSe) thin film cell not only lacks an energy band gradient which is controlled by a composition gradient in the absorption layer and is beneficial to carrier transportation, but also fails to reduce the interface recombination of carriers by forming a buried PN junction in an inversion mode on the surface of the absorption layer. And for Cu₂ZnSnSe₄(CZTSe) thin film battery Cu prepared by doping germanium (Ge) element of the same group instead of part of Sn element₂ZnSn1-xGexSe₄(CZTGSe) can be used to adjust the forbidden bandwidth, and CZTGSe has a band gap of greater than 10⁴cm^-1The light absorption coefficient of the material is rich in the earth crust, so the material has the advantages of rich resources, low cost of raw materials and the like, and is expected to become one of the best choices of the new generation of thin film solar cells.

Among the current teams for researching CZTGSe films, the M.Buffi re team of the university of Luwen in Belgium 2015 adopts magnetron sputtering Cu/Zn metal target materials and adopts electron beam evaporation to evaporate Ge layers, so that the influence of different selenization temperatures and deposition sequences on the performance of the CZGSe films is researched, and finally, the photoelectric conversion efficiency of 0.3 percent is obtained; in 2016, by sergio giraldo et al, spain, the prefabricated layer is prepared by magnetron sputtering of a metal target material, and Ge layers with different thicknesses are deposited on the top of the prefabricated layer by a thermal evaporation method, so that the influence of the Ge layers with different thicknesses on the CZTGSe thin film battery is researched, and the photoelectric conversion efficiency of the CZTGSe thin film battery with the optimal Ge thickness is determined to be 10.6%, which is also the highest photoelectric conversion efficiency of the current CZTGSe thin film battery. But still fails to meet the demand for thin film batteries.

Therefore, the invention provides a preparation method of a copper zinc tin germanium selenium absorption layer film with germanium gradient, which is based on the blocking mechanism of a molybdenum (Mo) blocking layer to fast diffusion metal, and forms the copper zinc tin germanium selenium absorption layer film with Ge component gradient on the back surface by inhibiting the diffusion speed of the fast diffusion metal Ge to the copper zinc tin selenium base film, thereby improving the carrier collection efficiency of the copper zinc tin selenium base film and further improving the performance of the film.

Disclosure of Invention

In view of the above, the present invention provides a method for preparing a cu-zn-sn-Ge-se absorption layer thin film with a Ge gradient, which can form a Ge concentration gradient on the back surface, and due to the formation of the Ge concentration gradient, a conduction band of the back surface is bent upwards, so as to form an electron blocking layer, thereby blocking the recombination of carriers at the interface of the back surface, improving the carrier collection efficiency of the cu-zn-sn-se based thin film, and further improving the performance of the thin film.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of a copper-zinc-tin-germanium-selenium absorption layer film with a germanium gradient specifically comprises the following steps:

(1) substrate pretreatment: cleaning and soaking the substrate, and blow-drying for later use;

(2) preparation of molybdenum and germanium layers: depositing a first molybdenum layer, a germanium layer and a second molybdenum layer on the pretreated substrate in sequence;

(3) preparing a copper-zinc-tin-sulfur prefabricated layer: performing multi-period step-by-step deposition on the second molybdenum layer according to the sequence of ZnS, CuS, Sn and CuS to obtain a copper-zinc-tin-sulfur prefabricated layer;

(4) preparing a copper-zinc-tin-germanium-selenium absorption layer film: and (3) carrying out heat treatment on the substrate subjected to the preparation of the copper-zinc-tin-sulfur prefabricated layer in the step (3) at 210 ℃ for 30min, then putting the substrate and selenium powder into a selenizing furnace, heating the substrate and selenium powder from room temperature to 550 ℃ at the heating rate of 20 ℃/min, preserving the heat for 10-13min, and naturally cooling the substrate to room temperature to obtain the copper-zinc-tin-germanium-selenium absorption layer film with the germanium gradient.

The preparation method is based on the blocking mechanism of the Mo blocking layer to the fast diffusion metal, and the copper zinc tin germanium selenium film with the Ge component gradient is formed on the back surface by inhibiting the diffusion speed of the fast diffusion metal Ge to the copper zinc tin selenium base film.

In the preparation process of the CZTSe prefabricated layer film, on one hand, a small amount of Ge element diffused from the bottom Mo layer is doped to replace part of Sn element, so that the forbidden bandwidth of the prepared film can be effectively increased, the band gap width of the back absorption layer is improved, and further, electrons are blocked from being diffused to the back; on the other hand, the work function of Mo is smaller than that of the CZTSe absorption layer, and the doping of Ge can properly increase the work function of the back electrode, so that the energy band arrangement of metal and semiconductor is optimized, the collection of carriers is facilitated, and the efficiency of the thin film solar cell is improved.

Preferably, the substrate is a soda lime glass substrate.

Preferably, the step of washing and soaking in the step (1) is as follows: the step of cleaning and soaking in the step (1) is as follows: sequentially cleaning the substrate with cleaning powder and washing powder, then ultrasonically cleaning the substrate with acetone and alcohol, then soaking the substrate in a potassium dichromate solution for 8-10h, and finally ultrasonically cleaning with deionized water.

Preferably, the ultrasonic cleaning time is 30min, and the concentration of the potassium dichromate solution is 0.4 mol/L.

The glass cleaned by the steps not only can remove dirt generated in the production process of the soda-lime glass, but also can remove oil stains and the like on the surface of the glass, so that the high cleanliness of the glass substrate is ensured, and the electrode characteristic with higher quality is realized.

Preferably, the deposition is performed by magnetron sputtering deposition.

The sample film is deposited by adopting a magnetron sputtering method under the low vacuum condition, so that higher cleanliness can be tested, and the influence of external impurities on the film quality is reduced.

Preferably, the thickness of the first molybdenum layer in the step (2) is 0.8 μm, and the thickness of the second molybdenum layer is 0.3 μm.

The first molybdenum layer improves the adhesion between the Mo electrode and the glass, and the second molybdenum layer can effectively reduce the diffusion of the Ge element to the absorption layer film, thereby being beneficial to forming the component gradient of the Ge element.

Preferably, the sputtering power of the germanium layer in the step (2) is 25W, and the deposition time is 20 min.

When the sputtering power of the Ge layer is fixed at 25W and the deposition time is different, the research shows that the deposition time is 20min, and the obtained sample film can better realize the composition gradient of the Ge element.

Preferably, the specific steps of each cycle are as follows: and respectively carrying out sputtering deposition on the target material on the second molybdenum layer according to the sequence of ZnS, CuS, Sn and CuS, wherein the sputtering power of each target material is 50W, and the sputtering time is 48min, 41min, 14min and 41min in sequence.

Preferably, the thickness of the copper zinc tin sulfide prefabricated layer in the step (3) is 1.2 μm.

The thickness of copper zinc tin sulfur prefabricated layer is 1.2 mu m, and the thickness of the selenized absorption layer film can be increased to 1.5-2 mu m, so that the solar spectrum can be absorbed more efficiently, and the photon loss is reduced.

Preferably, the molar relationship among the Cu, the Zn and the Sn elements in the copper-zinc-tin-sulfur pre-fabricated layer in the step (3) satisfies: Cu/Zn + Sn is 0.65, Zn/Sn is 1.

Cu suppression by designing preformed layer composition ratios that deviate from chemical composition ratios_ZnThe number of the defects of the reverse structure and the number of the deep energy level defects related to Sn are reduced, and simultaneously the composition range of the CZTSe thin film solar cell with the highest photoelectric conversion efficiency is met.

The copper-zinc-tin-germanium-selenium absorption layer film with the germanium gradient is applied to a solar cell.

According to the invention, by preparing the CZTGSe film with the component gradient, the combination of current carriers can be reduced, better film quality can be obtained, and a more efficient film solar cell is realized.

Compared with the prior art, the preparation method of the copper-zinc-tin-germanium-selenium absorption layer film with the germanium gradient has the following technical effects:

the invention realizes the energy band gradient which is beneficial to the carrier transportation and is regulated and controlled by the component gradient through the doping position of the Ge element and the proper annealing condition, thereby preparing the film material of the copper-zinc-tin-germanium-selenium absorption layer with the germanium gradient.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a graph of the band alignment of a Cu-Zn-Sn-Ge-Se absorber film with a Ge gradient prepared in example 1;

FIG. 2 is a surface view of an SEM of a Cu-Zn-Sn-Ge-Se absorber layer film with a Ge gradient prepared in example 1 (a);

FIG. 3 is a cross-sectional view (b) of an SEM of a Cu-Zn-Sn-Ge-Se absorber layer film with a Ge gradient prepared in example 1;

FIG. 4 is a grazing incidence angle XRD pattern of a Cu-Zn-Sn-Ge-Se absorber film with a Ge gradient prepared in example 1;

FIG. 5 is a J-V plot of solar cells of application examples versus comparative examples.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.