CN109841702A - Preparation method of alkali metal doped copper indium gallium selenide thin film solar cell absorber layer - Google Patents

Abstract

The invention relates to a method for preparing an absorption layer of an alkali metal doped copper indium gallium selenide thin film solar cell. The invention belongs to the technical field of thin film solar cells. Preparation method of alkali metal-doped copper indium gallium selenide thin film solar cell absorption layer: Step 1: Place Mo-coated polyimide, titanium foil or stainless steel foil substrate in a co-evaporation chamber; Step 2: Mo-coated under vacuum conditions Co-evaporate In, Ga, and Se materials on the back electrode for 2-4 minutes; Step 3: Co-evaporate Cu, In, Ga, and Se materials for 25-30 minutes; Step 4: Co-evaporate In, Ga, and Se materials for 6-9 minutes; Step 5: Co-evaporate NaF and Se materials for 8-12 minutes; Step 6: Co-evaporate KF and Se materials for 4-6 minutes; Step 7: Keep the substrate temperature at 340-360°C and stop heating the Se evaporation source until the temperature of the Se evaporation source is low. After heating to 160°C, the copper indium gallium selenide thin film absorption layer is prepared. The invention has the advantages of good interface crystallization quality, reducing interface recombination and ensuring good electrical properties on the surface of the absorption layer film.

Description

Preparation method of alkali metal doped copper indium gallium selenide thin film solar cell absorber layer

technical field

The invention belongs to the technical field of thin film solar cells, in particular to a preparation method of an alkali metal doped copper indium gallium selenide thin film solar cell absorber layer.

Background technique

Photovoltaic power generation is an energy utilization method that uses solar cells to convert solar energy into electrical energy. It has the advantages of no noise, no pollution, inexhaustible energy sources, and no geographical restrictions. It has been widely concerned and vigorously promoted.

Copper indium gallium selenide (CIGS) thin film solar cell is a quaternary compound solar cell with high mass specific power and light absorption coefficient, as well as good stability, anti-irradiation ability and low light characteristics. hot spot. In recent years, the development of copper indium gallium selenide thin film solar cells has made rapid progress, and the photoelectric conversion efficiency of single cells and modules has been continuously improved, which has become one of the mainstream development directions of the photovoltaic industry.

Alkali metal doping is an effective means to improve the performance of the absorber layer of copper indium gallium selenide thin film solar cells, and the doping process of sodium (Na) is currently widely used. Studies have shown that doping 0.01% to 0.1% of Na can effectively reduce the donor defects in the CIGS absorber layer, increase the hole concentration, and thus improve the electrical properties of the absorber layer. Photoelectric conversion efficiency is increased by 30% to 50%. The latest research results in recent years have shown that doping a certain amount of potassium (K) element in the copper indium gallium selenide absorber layer can also improve the photoelectric conversion efficiency of the cell. This is because on the one hand K element can promote the incorporation of gallium (Ga) element into copper. The indium gallium selenide lattice improves the tolerance of the absorber layer material to the Ga content, providing the possibility to prepare a high Ga absorber layer, which helps to improve the open circuit voltage of the solar cell; on the other hand, K element can promote buffering The cadmium (Cd) element in the layer diffuses into the copper indium gallium selenide absorber layer, thereby improving the crystal quality of the heterojunction interface and reducing the interface recombination.

For flexible substrates (polyimide, stainless steel, titanium foil, etc.) copper indium gallium selenide thin-film solar cells, since the substrate material does not contain alkali metal elements, it is impossible to realize the removal of alkali metals from the alkali metal during the preparation process like the soda-lime glass substrate. The substrate diffuses into the absorber layer, so artificial doping of alkali metals is required to improve the performance of solar cells. In the process of preparing the copper indium gallium selenide solar cell absorber layer by the co-evaporation method, the alkali metal doping can be pre-doping and co-doping (for the three-step co-evaporation copper indium gallium selenide process, it is divided into the first step of co-doping, The second-step co-doping, the third-step co-doping), post-doping and other methods, among which the pre-doping method and the co-doping method, the alkali metal will gather at the grain boundary to hinder the fusion between grains, thereby affecting the crystalline quality of the absorber layer. .

SUMMARY OF THE INVENTION

The present invention provides a preparation method of an alkali metal doped copper indium gallium selenide thin film solar cell absorber layer in order to solve the technical problems existing in the known technology.

The purpose of the present invention is to provide an alkali metal doped copper indium gallium selenide film with the characteristics of simple process, convenient operation, accurate control, good product interface crystal quality, reduced interface recombination, and good electrical properties on the surface of the absorption layer film. Preparation method of solar cell absorber layer.

Aiming at the method of doping a single type of alkali metal described in the inventions of application numbers CN201710099197.2 and CN201610333959.6, the invention proposes a process of sequentially doping Na and K in the copper indium gallium selenide absorber layer, and using K doping to improve the interface The crystalline quality also promotes the doping of Na and increases the carrier concentration. In addition, for the method of co-doping alkali metal in the third step described in the invention of application number CN201410724780.4, the present invention proposes a post-doping process of alkali metal Na and K, which can reduce the adverse effect of alkali metal doping on the crystal quality of the absorption layer. . The technical scheme adopted by the present invention for preparing the copper indium gallium selenide thin film solar cell:

The copper indium gallium selenide solar cell is a multi-layer structure, using polyimide (PI), stainless steel foil or titanium foil as the substrate. Copper indium gallium selenide absorber layer (about 1.8μm thick); 50nm thick n-type cadmium sulfide (CdS) buffer layer; 50nm thick intrinsic zinc oxide (i-ZnO) layer and 500nm thick transparent conductive thin film window layer; Nickel/Aluminum (Ni/Al) metal gate electrode.

The steps of the preparation method of the copper indium gallium selenide absorber layer film include:

Step 1. Place the Mo-coated substrate (polyimide, titanium foil or stainless steel foil) in the sample holder of the co-evaporation equipment chamber, the sample holder can be rotated; a substrate heating device is placed above the substrate; copper (Cu), gallium (Ga), indium (In), selenium (Se), potassium fluoride (KF), sodium fluoride (NaF) evaporation sources are evenly distributed under the evaporation chamber, and the evaporation source is equipped with a thermocouple for In order to monitor the evaporation temperature, there are evaporation source baffles between the substrate and the Cu, Ga, In, Se, KF, NaF evaporation sources;

Step 2. The evaporation chamber is evacuated to 8×10 ^-4 Pa by a vacuum pump, the substrate is heated to 380°C, and each evaporation source is heated at the same time (Cu 1150°C～1200°C, Ga 950°C～1000°C, In 830°C ℃～880℃, Se 220℃～250℃, NaF 750℃～800℃, KF 650℃～700℃), turn on the rotation function of the sample holder to ensure the uniformity of film formation, after the temperature of each evaporation source and substrate is stable Open the evaporation source baffles of In, Ga, and Se, and co-evaporate In, Ga, and Se materials on the Mo back electrode for 3 minutes;

Step 3. Close the In and Ga evaporation source baffles, lower the In and Ga evaporation source temperatures by 30°C respectively, and increase the substrate temperature to 510°C. After the evaporation source and substrate temperatures are stabilized, turn on the Cu, In, and Ga evaporation sources. Source baffle, co-evaporating Cu, In, Ga, Se materials for 25min;

Step 4. Close the evaporation source baffles of Cu, In, and Ga, stop the heating of the Cu evaporation source, increase the temperature of the In and Ga evaporation sources by 30°C respectively, and open the In and Ga evaporation source baffles after the evaporation source temperature is stable. Evaporate In, Ga, Se materials for 7 minutes;

Step 5. Close the In and Ga evaporation source baffles, stop the heating of the In and Ga evaporation sources, increase the temperature of the Se evaporation source by 20°C, and open the NaF evaporation source baffles after the evaporation source temperature is stable, and co-evaporate the NaF and Se materials for 10 min ;

Step 6, close the NaF evaporation source baffle, stop the NaF evaporation source heating, open the KF evaporation source baffle, and co-evaporate the KF and Se materials for 5min;

Step 7. Close the KF evaporation source baffle, stop the KF evaporation source heating, keep the temperature of the Se evaporation source unchanged, stop the substrate heating to rapidly cool down to 350 °C, turn on the substrate heating at this time, and keep the substrate temperature at 350 °C Keep the same, stop the heating of the Se evaporation source until the temperature of the Se evaporation source is lower than 160 °C, then close the Se evaporation source baffle, stop the heating of the substrate, stop the rotation of the substrate, take out the sample after the substrate is cooled, and the copper indium gallium selenide film absorbs Layer preparation is complete.

The technical scheme adopted in the preparation method of the alkali metal doped copper indium gallium selenide thin film solar cell absorber layer of the present invention is:

A preparation method of an alkali metal doped copper indium gallium selenide thin film solar cell absorber layer is characterized in that: the preparation method of the alkali metal doped copper indium gallium selenide thin film solar cell absorber layer includes the following process:

Step 1: Place the Mo-coated polyimide, titanium foil or stainless steel foil substrate in the sample holder of the co-evaporation chamber, and the sample holder can be rotated; a substrate heating device is placed above the substrate; Cu, Ga, In, Se, KF, NaF evaporation sources are evenly distributed under the evaporation chamber; evaporation source baffles are placed between the substrate and the evaporation source;

Step 2: Heat the substrate to 380-400°C under vacuum, and heat the evaporation source to Cu 1150°C～1200°C, Ga 950°C～1000°C, In 830°C～880°C, Se 220°C～250°C, NaF 750℃～800℃, KF650℃～700℃, turn on the rotation of the sample holder, open the evaporation source baffle of In, Ga and Se, and co-evaporate In, Ga and Se materials on the Mo back electrode for 2-4min;

Step 3: Close the In, Ga evaporation source baffles, lower the In, Ga evaporation source temperatures by 20-40 °C respectively, increase the substrate temperature to 500-520 °C, open the Cu, In, Ga evaporation source baffles, a total of Evaporate Cu, In, Ga, Se materials for 25-30min;

Step 4: Close the evaporation source baffles of Cu, In and Ga, stop the heating of the Cu evaporation source, increase the temperature of the In and Ga evaporation sources by 20-40°C respectively, open the In and Ga evaporation source baffles, and co-evaporate In and Ga , Se material 6-9min;

Step 5: close the In and Ga evaporation source baffles, stop the heating of the In and Ga evaporation sources, increase the temperature of the Se evaporation source by 15-25°C, open the NaF evaporation source baffles, and co-evaporate the NaF and Se materials for 8-12 minutes;

Step 6: Close the NaF evaporation source baffle, stop the NaF evaporation source heating, open the KF evaporation source baffle, and co-evaporate the KF and Se materials for 4-6 minutes;

Step 7: Close the KF evaporation source baffle, stop the KF evaporation source heating, keep the temperature of the Se evaporation source unchanged, stop the substrate heating to cool it down to 340-360 °C, turn on the substrate heating at this time, and keep the substrate temperature at 340 °C -360 °C unchanged, stop the Se evaporation source heating, until the Se evaporation source temperature is lower than 160 °C, close the Se evaporation source baffle, stop the substrate heating, and the preparation of the copper indium gallium selenide thin film absorption layer is completed.

The preparation method of the alkali metal doped copper indium gallium selenide thin film solar cell absorber layer of the present invention can also adopt the following technical solutions:

The preparation method of the alkali metal doped copper indium gallium selenide thin film solar cell absorber layer is characterized in that: in step 1, the Cu, Ga, In, Se, KF, NaF evaporation source is equipped with a thermocouple for monitoring the evaporation temperature .

The preparation method of the alkali metal doped copper indium gallium selenide thin film solar cell absorber layer is characterized in that: in step 2, a vacuum pump is used to evacuate the evaporation chamber to 8×10 ^-4 Pa under vacuum conditions.

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

Compared with the prior art, compared with the prior art, the present invention has the following obvious features:

1. Compared with the method of doping a single type of alkali metal described in the inventions of application numbers CN201710099197.2 and CN201610333959.6, the invention proposes a process of sequentially doping Na and K in the copper indium gallium selenide absorption layer. Hetero K elements can improve the crystal quality of the interface between the copper indium gallium selenide absorber layer and the CdS buffer layer, reduce the interface recombination, and can promote the diffusion of Ga, and improve the tolerance of the absorber layer material to the Ga content. At the same time, studies have shown that K can promote the doping of Na. Doping K on the basis of Na doping can further enhance the effect of Na element in passivating the donor defect of the absorber layer and increasing the carrier concentration.

2. Compared with the method of co-doping alkali metals in the third step described in the invention of application number CN201410724780.4, the present invention adopts the process of post-doping Na and K of alkali metals, and co-evaporating the copper indium gallium selenide absorption layer process in a three-step method Alkali metal doping is performed after all the steps are completed. In this method, larger crystal grains have been formed in the absorber layer before doping, the alkali metal will not affect the crystallization process, and better crystalline quality can be obtained than the co-doping method.

3. In the currently commonly used alkali metal doping process, an annealing process is required after doping. This process requires a high concentration of Se in the evaporation chamber. Insufficient Se concentration will cause In and Ga and Se elements are lost at high substrate temperature, resulting in Cu-rich short circuit on the surface. The invention adopts the method of rapid cooling after doping is completed, and rapidly reduces the substrate temperature to 350° C. in the Se atmosphere to reduce the loss of In, Ga, and Se elements at high temperature, and ensures that the surface of the absorption layer film has good electrical properties.

Description of drawings

1 is a schematic side view of the structure of a vacuum chamber used for the preparation method of the alkali metal doped copper indium gallium selenide thin film solar cell absorber layer of the present invention;

FIG. 2 is a schematic structural diagram of a copper indium gallium selenide thin film solar cell prepared by the present invention.

In the figure, 1-evaporation chamber; 2-substrate heating device; 3-Mo plating substrate; 4-sample holder; 5-vacuum pump; 6-Cu evaporation source; 7-Ga evaporation source; 8-In evaporation source; 9-Se evaporation source; 10-NaF evaporation source; 11-KF evaporation source; 12-evaporation source baffle; 13-substrate; 14-Mo back electrode; 15-CIGS absorber layer; 16-CdS buffer layer ; 17-intrinsic i-ZnO layer; 18-transparent conductive film; 19-Ni/Al gate electrode.

Detailed ways

In order to further understand the content of the invention, features and effects of the present invention, the following embodiments are exemplified and described in detail with the accompanying drawings as follows:

See Figures 1 and 2.

Example 1

A preparation method of an alkali metal doped flexible substrate copper indium gallium selenide thin film solar cell absorber layer, using polyimide as the substrate 13, and depositing a 1 μm thick Mo back on the substrate 13 by a method of magnetron sputtering electrode 14; prepare a copper indium gallium selenide absorption layer 15 on the Mo back electrode; the preparation process of the copper indium gallium selenide absorption layer 15 is as follows:

(1) Place the Mo-coated substrate 3 in the sample holder 4 of the co-evaporation equipment chamber 1, and the sample holder can be rotated; a substrate heating device 2 is placed above the substrate; Cu evaporation source 6, Ga evaporation source 7 , In evaporation source 8, Se evaporation source 9, NaF evaporation source 10, KF evaporation source 11 are evenly distributed under the evaporation chamber, the evaporation source is equipped with a thermocouple for monitoring the evaporation temperature, the substrate and Cu, Ga, In, Evaporation source baffles 12 are arranged between the Se, KF and NaF evaporation sources;

(2) The evaporation chamber is evacuated to 8×10 ^-4 Pa by the vacuum pump 5, the substrate is heated to 380°C, and each evaporation source is heated (Cu 1150°C～1200°C, Ga 950°C～1000°C, In 830°C～880°C, Se 220°C～250°C, NaF 750°C～800°C, KF 650°C～700°C), turn on the rotation function of sample holder 4 to ensure the uniformity of film formation, wait for the temperature of each evaporation source and substrate After stabilization, open the evaporation source baffles of In, Ga, and Se, and co-evaporate In, Ga, and Se materials on the Mo back electrode for 3 min;

(3) Close the In and Ga evaporation source baffles, lower the temperatures of the In evaporation source 8 and the Ga evaporation source 7 by 30°C respectively, and increase the substrate temperature to 510°C. After the evaporation source and substrate temperatures are stabilized, the Cu is turned on. , In, Ga evaporation source baffle, co-evaporation of Cu, In, Ga, Se materials for 25min;

(4) Close the baffles of the Cu, In, Ga evaporation sources, stop the heating of the Cu evaporation source 6, increase the temperature of the In evaporation source 8 and the Ga evaporation source 7 by 30°C respectively, and turn on the In, Ga evaporation after the evaporation source temperature is stable Source baffle, co-evaporating In, Ga, Se materials for 7min;

(5) Close the In and Ga evaporation source baffles, stop the heating of the In evaporation source 8 and the Ga evaporation source 7, increase the temperature of the Se evaporation source 9 by 20°C, open the NaF evaporation source baffle after the evaporation source temperature is stable, and co-evaporate NaF, Se material 10min;

(6) close NaF evaporation source baffle, stop NaF evaporation source 10 heating, open KF evaporation source baffle, co-evaporate KF, Se material 5min;

(7) Close the KF evaporation source baffle, stop the heating of the KF evaporation source 11, keep the temperature of the Se evaporation source 9 unchanged, stop the heating of the substrate to make it rapidly cool down to 350°C, turn on the heating of the substrate at this time, and keep the temperature of the substrate at 350 ° C remains unchanged, stop the heating of the Se evaporation source 9, and close the Se evaporation source baffle until the temperature of the Se evaporation source 9 is lower than 160 ° C, stop the heating of the substrate, stop the rotation of the substrate, take out the sample after the substrate is cooled, and obtain Alkali metal doped copper indium gallium selenide thin film absorber layer 15 .

Then, on the copper indium gallium selenide absorber layer, a 50 nm thick CdS buffer layer 16 is deposited by a chemical water bath method, a 50 nm thick intrinsic i-ZnO layer 17 and a 500 nm thick Al- The ZnO transparent conductive layer 18 and the Ni/Al gate electrode 19 are evaporated to obtain a copper indium gallium selenide thin film solar cell on a polyimide substrate. The cell structure is shown in FIG. 2 .

Example 2

A preparation method of an alkali metal doped flexible substrate copper indium gallium selenide thin film solar cell absorber layer, using a stainless steel foil with a thickness of 40 μm as the substrate, other conditions are the same as in Example 1, to prepare a stainless steel substrate structure copper indium gallium Selenium thin-film solar cells.

Example 3

A preparation method of an alkali metal doped flexible substrate copper indium gallium selenide thin film solar cell absorber layer, using a titanium foil with a thickness of 40 μm as the substrate, other conditions are the same as in Example 1, to prepare a titanium substrate structure copper indium gallium Selenium thin-film solar cells.

This embodiment has the positive effects of simple process, convenient operation, accurate control, good product interface crystal quality, reduced interface recombination, and good electrical properties of the surface of the absorbing layer film.

Claims (3)

1. a preparation method of alkali metal doped copper indium gallium selenide thin film solar cell absorption layer, it is characterized in that: the preparation method of alkali metal doped copper indium gallium selenide thin film solar cell absorption layer comprises the following technological process: Step 1: Place the Mo-coated polyimide, titanium foil or stainless steel foil substrate in the sample holder of the co-evaporation chamber, and the sample holder can be rotated; a substrate heating device is placed above the substrate; Cu, Ga, In, Se, KF, NaF evaporation sources are evenly distributed under the evaporation chamber; evaporation source baffles are placed between the substrate and the evaporation source; Step 2: Heat the substrate to 380-400°C under vacuum, and heat the evaporation source to Cu 1150°C～1200°C, Ga 950°C～1000°C, In 830°C～880°C, Se 220°C～250°C, NaF 750℃～800℃, KF 650℃～700℃, turn on the rotation of the sample holder, open the evaporation source baffles of In, Ga and Se, and co-evaporate In, Ga and Se materials on the Mo back electrode for 2-4min; Step 3: Close the In, Ga evaporation source baffles, lower the In, Ga evaporation source temperatures by 20-40 °C respectively, increase the substrate temperature to 500-520 °C, open the Cu, In, Ga evaporation source baffles, a total of Evaporate Cu, In, Ga, Se materials for 25-30min; Step 4: Close the evaporation source baffles of Cu, In and Ga, stop the heating of the Cu evaporation source, increase the temperature of the In and Ga evaporation sources by 20-40°C respectively, open the In and Ga evaporation source baffles, and co-evaporate In and Ga , Se material 6-9min; Step 5: close the In and Ga evaporation source baffles, stop the heating of the In and Ga evaporation sources, increase the temperature of the Se evaporation source by 15-25°C, open the NaF evaporation source baffles, and co-evaporate the NaF and Se materials for 8-12 minutes; Step 6: Close the NaF evaporation source baffle, stop the NaF evaporation source heating, open the KF evaporation source baffle, and co-evaporate the KF and Se materials for 4-6 minutes; Step 7: Close the KF evaporation source baffle, stop the KF evaporation source heating, keep the temperature of the Se evaporation source unchanged, stop the substrate heating to cool it down to 340-360 °C, turn on the substrate heating at this time, and keep the substrate temperature at 340 °C -360 °C unchanged, stop the Se evaporation source heating, until the Se evaporation source temperature is lower than 160 °C, close the Se evaporation source baffle, stop the substrate heating, and the preparation of the copper indium gallium selenide thin film absorption layer is completed. 2. The preparation method of the alkali metal doped copper indium gallium selenide thin film solar cell absorber layer according to claim 1, wherein in step 1, the Cu, Ga, In, Se, KF, NaF evaporation sources are equipped with heat Coupled to monitor evaporation temperature. 3 . The method for preparing an absorbing layer of an alkali metal doped copper indium gallium selenide thin film solar cell according to claim 1 , wherein in step 2, the vacuum condition adopts a vacuum pump to evacuate the evaporation chamber to 8×10 ⁻⁴ . Pa.