CN105679878A - Method for preparing absorption layer of CZTSSe thin film solar cell by co-evaporation - Google Patents

Abstract

The invention relates to a method for co-evaporating to prepare an absorbing layer of a copper-zinc-tin-sulfur-selenium thin-film solar cell. The invention belongs to the technical field of thin film solar cells. A method for co-evaporating an absorbing layer of a copper-zinc-tin-sulfur-selenium thin-film solar cell, the copper-zinc-tin-sulfur-selenium thin-film solar cell has a multilayer structure; preparation steps: 1. Place a Mo-plated substrate in a co-evaporation equipment chamber , Cu, ZnS, Sn, and Se evaporation sources are distributed under the evaporation chamber; 2. Vacuumize the evaporation chamber to 3×10 ^-4 Pa, heat the substrate to 500°C, heat each evaporation source, and share on the Mo back electrode. Evaporate Cu, ZnS, Sn, Se; 3. Stop the heating of Cu, ZnS evaporation source, and co-evaporate Sn and Se; 4. Stop the heating of Sn evaporation source until the substrate temperature is lower than 300 ° C, stop the heating of Se evaporation source, and wait for the substrate Remove from cooling. The invention has the advantages of effectively suppressing the re-evaporation of Zn element, obtaining a copper-zinc-tin-sulfur-selenide thin film material whose composition is close to the stoichiometric ratio, high crystallization quality of the thin film, good uniformity and photoelectric performance, and the like.

Description

A kind of co-evaporation method for preparing copper-zinc-tin-sulfur-selenium thin-film solar cell absorber layer

technical field

The invention belongs to the technical field of thin-film solar cells, in particular to a method for co-evaporating an absorbing layer of a copper-zinc-tin-sulfur-selenium thin-film solar cell.

Background technique

At present, copper-zinc-tin-sulfur (CZTS) thin-film solar cells are considered to be one of the most promising directions among various compound semiconductor solar cells. Copper zinc tin sulfur is a p-type direct bandgap quaternary compound semiconductor material with a kesterite or stannite structure, and its light absorption coefficient can reach 10 ⁴ cm ^-1 , which is suitable for use as Thin-film solar cell absorber layer, theoretical research shows that the ultimate photoelectric conversion efficiency of copper-zinc-tin-sulfur thin-film solar cells is as high as 32.2%. Compared with copper indium gallium selenide (CIGS) solar cells that use the rare element indium (In), zinc (Zn) and tin (Sn) materials used in copper zinc tin sulfur solar cells are abundant in the earth's crust, cheap, and It is non-toxic and has little impact on the ecological environment, making copper-zinc-tin-sulfur materials gradually become a hot spot in the field of solar cell research in recent years.

The copper zinc tin sulfur selenium (CZTSSe) material is a solar cell absorber material formed by partially replacing the sulfur (S) element in the copper zinc tin sulfur material with selenium (Se) element. Doping Se elements can improve the defect characteristics of the material and reduce the defect density as a recombination center, thereby reducing carrier recombination, improving the electrical properties of the material, and increasing the photoelectric conversion efficiency of the battery. The photoelectric conversion efficiency of copper-zinc-tin-sulfur-selenium thin-film solar cells reported so far has reached 12.6%.

The preparation methods of copper-zinc-tin-sulfur-selenium thin film materials are divided into two categories: vacuum method and non-vacuum method. Among them, the co-evaporation method, as one of the vacuum deposition methods, has the advantages of simple method, no post-sulfurization (selenization) process, good repeatability, etc., and because the film is formed by direct evaporation of raw materials in a vacuum sealed environment, no To strong toxic substances, safer and more environmentally friendly. The currently used co-evaporation process uses simple metal Zn as the evaporation raw material. Since the evaporation temperature of metal Zn is lower than 500 ° C, when the substrate temperature reaches 500 ° C required for the preparation of copper-zinc-tin-sulfur-selenium materials, the deposited Zn will be removed from the surface of the film Re-evaporation causes the loss of Zn element; in addition, metal Sn reacts with S and Se to form binary phases SnSe and SnS that are also easy to re-evaporate from the substrate surface, which will lead to the loss of Sn element, and the film composition is difficult to control, etc. technical problem.

Contents of the invention

In order to solve the technical problems in the known technology, the invention provides a method for co-evaporating and preparing the absorbing layer of a copper-zinc-tin-sulfur-selenium thin film solar cell.

The purpose of the present invention is to provide a kind of material that can effectively suppress the re-evaporation of Zn element and obtain a copper-zinc-tin-sulfur-selenium film material with a composition close to the stoichiometric ratio, and promote the sufficient diffusion and combination of each element in the film, thereby improving the crystal quality of the film and improving the copper The invention discloses a method for preparing a copper-zinc-tin-sulfur-selenium thin-film solar cell absorber layer by co-evaporation with the characteristics of zinc-tin-sulfur-selenide material uniformity and photoelectric performance.

The present invention adopts multi-source co-evaporation to prepare copper-zinc-tin-sulfur-selenium absorbing layer thin film, and selects zinc sulfide (ZnS) compound whose evaporation temperature exceeds 700°C to replace metal Zn as the evaporation raw material, and ZnS reacts with other elements to form kesterite CZTSSe structure , there is no elemental Zn formation during the film deposition process, which can effectively inhibit the re-evaporation of Zn elements; at the same time, the process steps of post-annealing under Sn and Se atmospheres are designed for the re-evaporation of SnSe and SnS, which can effectively replenish the lost Zn during the film deposition process. Sn element, the copper zinc tin sulfur selenium thin film material whose composition is close to the stoichiometric ratio is obtained.

The technical scheme adopted by the method for co-evaporation of the present invention to prepare copper-zinc-tin-sulfur-selenium thin-film solar cell absorbing layer is:

A method for co-evaporating an absorbing layer of a copper-zinc-tin-sulfur-selenium thin-film solar cell is characterized in that: the copper-zinc-tin-sulfur-selenium thin-film solar cell is a multilayer structure, using soda-lime glass, stainless steel foil or titanium foil as a substrate, and The upper structure is molybdenum back electrode, p-type copper zinc tin sulfur selenide absorbing layer, n type cadmium sulfide buffer layer, intrinsic zinc oxide layer and transparent conductive thin film window layer, nickel/aluminum metal gate electrode; copper zinc tin sulfur selenium thin film The preparation method of the solar cell absorbing layer comprises process steps:

Step 1. Place the Mo-plated substrate in the sample holder of the co-evaporation equipment chamber. The sample holder is rotatable; a substrate heating device is placed above the substrate; Cu, ZnS, Sn, Se evaporation sources are evenly distributed in the evaporation Below the chamber, a thermocouple is installed inside the evaporation source to monitor the evaporation temperature, and evaporation source baffles are placed between the substrate and the evaporation sources of Cu, ZnS, Sn, and Se;

Step 2. Use a vacuum pump to evacuate the evaporation chamber to 3×10 ^-4 Pa, heat the substrate to 500°C, and heat each evaporation source at Cu1120°C-1180°C, ZnS700°C-780°C, and Sn1100°C-1150°C , Se200℃～250℃, turn on the sample holder rotation function to ensure the uniformity of film formation, open the evaporation source baffles of Cu, ZnS, Sn, Se after the temperature of each evaporation source and the substrate are stable, and make a total of Evaporate Cu, ZnS, Sn, Se materials for 45 minutes;

Step 3. Keep the substrate temperature at 500°C, close the Cu and ZnS evaporation source baffles, stop the Cu and ZnS evaporation source heating, co-evaporate Sn and Se elements for 15 minutes, complete the annealing process in the Sn and Se atmosphere, and supplement the deposition process in step 2 The Sn element lost due to re-evaporation of SnS and SnSe;

Step 4. Close the Sn evaporation source baffle, stop the heating of the Sn evaporation source, and lower the temperature of the substrate at a rate of 20-30°C/min in the Se atmosphere until the substrate temperature is lower than 300°C, then close the Se evaporation source baffle, Stop the heating of the Se evaporation source, stop the rotation of the substrate, take it out after the substrate is cooled, and the preparation of the copper-zinc-tin-sulfur-selenide film absorption layer is completed.

The method for preparing copper-zinc-tin-sulfur-selenium thin-film solar cell absorbing layer by co-evaporation of the present invention can also adopt the following technical scheme:

The method for preparing the absorbing layer of a copper-zinc-tin-sulfur-selenium thin-film solar cell by co-evaporation is characterized in that: the thickness of the molybdenum back electrode on the copper-zinc-tin-sulfur-selenium thin-film solar cell substrate is 0.7-1.2 μm; p-type copper-zinc-tin-sulfur-selenide The thickness of the absorption layer is 1.0-1.4 μm; the n-type cadmium sulfide buffer layer is 45-55nm thick; the intrinsic zinc oxide layer is 45-55nm thick and the transparent conductive film window layer is 300-500nm thick.

The advantages and positive effects that the present invention has are:

Co-evaporation method for preparing copper-zinc-tin-sulfur-selenium thin-film solar cell absorbing layer is due to adopting the brand-new technical scheme of the present invention, compared with the prior art, the present invention has the following characteristics:

1. In view of the problem that the substrate temperature reaches 500°C during the deposition process of the copper-zinc-tin-sulfur-selenium thin film, which exceeds the evaporation temperature of metal Zn and causes Zn to re-evaporate from the substrate surface. In this invention, the compound ZnS with an evaporation temperature exceeding 700°C is used to replace metal Zn Co-evaporation raw materials are used to prepare copper-zinc-tin-sulfur-selenium thin-film solar cell absorber layer. ZnS reacts with other elements to form a CZTSSe film with kesterite structure. No elemental Zn is formed during the film deposition process, which can effectively inhibit the re-evaporation of Zn elements.

2. Aiming at the problem that metal Sn reacts with S and Se to form binary phases SnSe and SnS whose evaporation temperature is lower than 500°C, the binary phase is easy to re-evaporate from the surface of the film, resulting in the loss of Sn element. The process step of post-annealing under the Sn and Se atmosphere after the evaporation step is completed can effectively replenish the Sn element lost during the film deposition process, and obtain a copper-zinc-tin-sulfur-selenium film material with a composition close to the stoichiometric ratio.

3. The present invention adopts the process steps of post-annealing under Sn and Se atmosphere, which helps to promote the full diffusion and combination of elements in the film, thereby improving the crystal quality of the film, and improving the uniformity and photoelectric performance of the copper-zinc-tin-sulfur-selenide material.

Description of drawings

Fig. 1 is the schematic diagram of the side view structure of the vacuum chamber used in the present invention;

Fig. 2 is the structural representation of the copper zinc tin sulfur selenium thin film solar cell prepared by the present invention;

Fig. 3 is the X-ray diffraction pattern (XRD) of the copper zinc tin sulfur selenium thin film prepared according to embodiment 1;

FIG. 4 is a scanning electron microscope (SEM) photograph of a cross-section of the copper-zinc-tin-sulfur-selenide thin film prepared according to Example 1.

In the figure, 1-evaporation chamber; 2-substrate heating device; 3-Mo-coated substrate; 4-sample holder; 5-vacuum pump; 6-Cu evaporation source; 7-ZnS evaporation source; 8-Sn evaporation source; 9-Se evaporation source; 10-evaporation source baffle; 11-substrate; 12-Mo back electrode; 13-copper zinc tin sulfur selenium absorber layer; 14-CdS buffer layer; 15-intrinsic i-ZnO layer; 16 - transparent conductive film; 17 - Ni/Al gate electrode.

detailed description

In order to further understand the invention content, characteristics and effects of the present invention, the following examples are given, and detailed descriptions are as follows in conjunction with the accompanying drawings:

Refer to accompanying drawing 1, Fig. 2, Fig. 3 and Fig. 4.

Example 1

A method for preparing copper-zinc-tin-sulfur-selenium thin-film solar cell absorber layer by co-evaporation, using soda-lime glass as the substrate 11, and depositing a 1 μm thick Mo back electrode 12 on the substrate by magnetron sputtering; Copper-zinc-tin-sulfur-selenium absorbing layer is prepared on the electrode; the preparation process of the copper-zinc-tin-sulfur-selenium absorbing layer is: (1) the substrate of Mo plating is placed in the sample rack 4 of co-evaporation equipment chamber, and sample rack can be rotation; a substrate heating device 2 is placed above the substrate; Cu evaporation source 6, ZnS evaporation source 7, Sn evaporation source 8, and Se evaporation source 9 are evenly distributed under the evaporation chamber, and the inside of the evaporation source is equipped with a thermocouple for Monitor the evaporation temperature, and place evaporation source baffles 10 between the substrate and the evaporation sources of Cu, ZnS, Sn, and Se; (2) Vacuumize the evaporation chamber to 3×10 ^-4 Pa with a vacuum pump, and place the substrate 3 Heating to 500°C, heating each evaporation source at the same time, heating Cu evaporation source 6 to 1120°C-1180°C, heating ZnS evaporation source 7 to 700°C-780°C, heating Sn evaporation source 8 to 1100°C-1150°C, heating Se Evaporation source 9 to 200 ° C ~ 250 ° C; turn on the sample holder rotation function to ensure the uniformity of film formation, and open the evaporation source baffles 10 of Cu, ZnS, Sn, and Se after the temperature of each evaporation source and the substrate is stable. Co-evaporate Cu, ZnS, Sn, and Se materials on the back electrode for 45 minutes; (3) Keep the substrate 3 temperature at 500°C, close the Cu, ZnS evaporation source baffle, stop the Cu, ZnS evaporation source heating, and co-evaporate Sn, Se Element 15min, complete the annealing process under the Sn, Se atmosphere, supplement the Sn element lost due to the re-evaporation of SnS and SnSe in the deposition process of the previous step; (4) close the Sn evaporation source baffle, stop the heating of the Sn evaporation source, and the substrate 3 Lower the temperature at a rate of 20-30°C/min in the Se atmosphere until the substrate temperature is lower than 300°C, then close the Se evaporation source baffle, stop the Se evaporation source heating, stop the substrate rotation, and take out the substrate after cooling. A copper-zinc-tin-sulfur-selenide film absorbing layer 13 with a composition close to the stoichiometric ratio is obtained. From the XRD pattern shown in Figure 3, it can be seen that the characteristic peaks of the film are consistent with the kesterite structure. From the SEM photo of the cross-section shown in Figure 4, it can be seen that the thickness of the film is close to 1.2 μm, and it has good crystal quality.

Then on the copper-zinc-tin-sulfur-selenium absorption layer, use known technology successively, deposit 50nm thick CdS buffer layer 14 with chemical water bath method, deposit 50nm thick intrinsic i-ZnO layer 15 and 500nm thick Al with magnetron sputtering method - ZnO transparent conductive layer 16, evaporation of Ni/Al electrode 17 to obtain copper zinc tin sulfur selenium thin film solar cell.

Example 2

A stainless steel foil with a thickness of 40 μm was used as the substrate, and the other conditions were the same as in Example 1, and a copper-zinc-tin-sulfur-selenium thin-film solar cell with a stainless steel substrate structure was prepared.

Example 3

A titanium foil with a thickness of 40 μm was used as the substrate, and other conditions were the same as in Example 1 to prepare a copper-zinc-tin-sulfur-selenium thin-film solar cell with a titanium substrate structure.

This embodiment can effectively suppress the re-evaporation of the Zn element, obtain a copper-zinc-tin-sulfur-selenium film material with a composition close to the stoichiometric ratio, and promote the full diffusion and combination of each element in the film, thereby improving the crystal quality of the film and improving the copper-zinc-tin Positive effects such as uniformity and optoelectronic properties of sulfur-selenide materials.

Claims (2)

1. the method that a coevaporation prepares copper zinc tin sulfur selenium absorption layer of thin film solar cell, it is characterized in that: copper-zinc-tin-sulfur selenium film solar battery is multiple structure, adopting soda-lime glass, stainless steel foil or titanium foil as substrate, on it, structure is followed successively by molybdenum back electrode, p-type copper zinc tin sulfur selenium absorbed layer, n-type cadmium sulfide cushion, native oxide zinc layers and transparent conductive film Window layer, nickel aluminum metal gate electrode;The preparation method of copper zinc tin sulfur selenium absorption layer of thin film solar cell includes processing step:

Step 1, by plating Mo substrate be placed in the specimen holder of coevaporation apparatus cavity, specimen holder is rotatable; The top of substrate is equipped with lining heat; Cu, ZnS, Sn, Se evaporation source is evenly distributed on below evaporation chamber, is furnished with thermocouple for monitoring evaporating temperature, is all equipped with evaporation source baffle plate between substrate and Cu, ZnS, Sn, Se evaporation source inside evaporation source;

Step 2, it is evacuated to 3 × 10 by vacuum pump by evaporation cavity^-4Pa, by silicon to 500 DEG C, each evaporation source is heated Cu1120 DEG C～1180 DEG C, ZnS700 DEG C～780 DEG C, Sn1100 DEG C～1150 DEG C, Se200 DEG C～250 DEG C simultaneously, open specimen holder spinfunction to ensure the uniformity of film forming, the evaporation source baffle plate of Cu, ZnS, Sn, Se, coevaporation Cu, ZnS, Sn, Se material 45min on Mo back electrode is opened after stable with underlayer temperature until each evaporation source;

Step 3, maintenance underlayer temperature 500 DEG C, close Cu, ZnS evaporation source baffle plate, stop the heating of Cu, ZnS evaporation source, coevaporation Sn, Se element 15min, complete annealing process under Sn, Se atmosphere, supplement the Sn element run off due to SnS, SnSe re-evaporation in step 2 deposition process;

Step 4, closedown Sn evaporation source baffle plate, stop the heating of Sn evaporation source, substrate is lowered the temperature with the speed of 20-30 DEG C/min under Se atmosphere, until underlayer temperature lower than 300 DEG C after close the evaporation source baffle plate of Se, stop the heating of Se evaporation source, stop substrate rotating, take out after substrate cools down, prepared by copper zinc tin sulfur selenium film absorption layer.

2. the method that coevaporation according to claim 1 prepares copper zinc tin sulfur selenium absorption layer of thin film solar cell, is characterized in that: molybdenum back electrode thickness 0.7-1.2 μm on copper-zinc-tin-sulfur selenium film solar battery substrate; P-type copper zinc tin sulfur selenium absorber thickness is 1.0-1.4 μm; The n-type cadmium sulfide cushion that 45-55nm is thick; The native oxide zinc layers of 45-55nm thickness and the transparent conductive film Window layer of 300-500nm thickness.