CN1367536A - Copper-indium-galliun-selenium film solar cell and its preparation method - Google Patents

Abstract

A copper indium gallium selenium thin film solar cell and a preparation method thereof, relating to the preparation of a semiconductor thin film and the structural design of a semiconductor thin film device. The feature of the present invention is to use n-type zinc sulfide (ZnS) as the window layer and copper indium gallium selenide P-type semiconductor film as the absorption layer to form a ZnS/Cu(In,Ga)Se ₂ p-n junction with ZnS, and its metal The back electrode is molybdenum-copper alloy (Mo-Cu). In the present invention, ZnS is used instead of ZnO and other materials as the window layer of the thin-film solar cell, which increases the solar light absorption spectrum range of the absorbing layer and avoids the use of harmful substances containing heavy metal Cd; the back electrode uses Mo-Cu alloy instead of Mo , making the combination between the battery and the substrate more firm, and improving the yield of the battery. Therefore, the invention has the advantages of simple structure, high light conversion efficiency, good stability, no pollution, simple process and the like.

Description

A copper indium gallium selenide thin film solar cell and its preparation method

technical field

The invention belongs to the technical field of optoelectronic materials and new energy, and relates to the preparation of semiconductor thin films and the structural design of semiconductor thin film devices, in particular to the structural design and preparation method of thin-film solar cells using copper indium gallium selenium thin films as absorbing layers.

Background technique

Thin-film solar cells with chalcopyrite structure compound semiconductor copper indium selenide (CuInSe ₂ , referred to as CIS) or copper indium gallium selenide (Cu(In, Ga)Se ₂ , referred to as CIGS) film with gallium in solid solution as the light absorption layer Not only has high energy conversion efficiency, but also has radiation stability, so it has become one of the research hotspots in the field of photovoltaic cells. Copper indium gallium selenide (CIGS) solar cells are photovoltaic devices formed by depositing multi-layer thin films on glass or other cheap substrates. Transition layer/light absorption layer (CIGS, CIS)/metal back electrode/substrate. After years of research, CIGS solar cells have developed different structures, the main difference lies in the choice of window materials. The earliest is to use CdS as the window. As reported in patent US3978510, the absorption layer of the thin-film battery is p-type CuInSe ₂ , the window layer is n-type CdS, and gold and indium are respectively used as electrode terminals. The battery structure reported in the patent US4465575 is: antireflection film/metal grid electrode (Al)/window layer (CdS)/light absorbing layer (CIS)/metal back electrode (Mo)/substrate. The battery structure in the patent US4335266 is: anti-reflection film/metal grid electrode/window layer (CdS)/light absorbing layer (CIGS)/metal back electrode/substrate. The difference from the aforementioned patent is that in the US4335266 patent, the window layer is It is composed of two layers of CdS with different resistivities.

The further research result is to replace CdS with CdZnS as the window layer. As mentioned in the patent US4611091, the window layer used in the battery can be n-type semiconductor CdS, CdZnS, ZnSe, CdSe, etc. In view of the fact that the heavy metal Cd is harmful to the human body and pollutes the environment, and the CdS material itself has a narrow bandgap, the window layer has been replaced by ZnO material with a bandgap of 3.3eV in recent years. However, when using ZnO as the window layer, in order to ensure the excellent performance of the battery Performance, generally must use one deck thinner CdS layer as the buffer layer that ZnO contacts with CIGS, as the battery structure reported in patent WO 97/22152 is: anti-reflection film/metal grid electrode/transparent electrode layer (doped with Al ZnO, referred to as ZAO)/window layer (ZnO)/transition layer (CdS)/light absorbing layer (CIGS)/metal back electrode (Mo)/glass. This is also the most common CIGS thin-film battery structure at present. Also useful other materials are used as the transition layer, as the battery structure reported in patent CN12300031A is: metal electrode/transparent electrode layer (indium tin oxide, referred to as ITO)/window layer (ZnO)/transition layer/light absorption layer (P-type CIGS) /Metal back electrode (Mo)/substrate, wherein the transition layer material used is n-type compound semiconductor and n-type semiconductor compound film. The n-type compound semiconductor material contains at least one of Cu, In and Ga, at least one of Se and S, and at least one of Mg, Zn and Cd. The n-type semiconductor material may be ZnO, Zn(O, OH), Zn(O, OH, S), ZnIn _{x Se} , etc.

In addition, the back electrode of the battery is generally made of metal molybdenum, such as the back electrode of the CIGS thin film solar cell in patent US3978510, patent US4465575 and patent US4335266. Patent WO 97/22152 reports that a metal copper layer is coated on the molybdenum layer by electrodeposition to make a metal composite layer as a back electrode, but this increases the process and increases the production cost.

Contents of the invention

The purpose of the present invention is to provide a novel structure copper indium gallium selenide thin film solar cell and its preparation method, which can not only improve the photoelectric conversion efficiency of the cell, but also completely avoid the use of harmful substances containing heavy metal Cd such as CdS or CdZnS, which is useful. Conducive to environmental protection.

The present invention is achieved through the following technical solutions: a copper indium gallium selenium thin film solar cell, which is composed of an anti-reflection film, a transparent electrode layer, a window layer, a transition layer, a light absorption layer, a metal back electrode and a substrate in sequence, and its features In that: the window layer is an n-type zinc sulfide (ZnS) thin film.

On the basis of the above solution, the present invention uses a p-type copper indium gallium selenide (CIGS) layer as an absorption layer to form a ZnS/Cu(In, Ga)Se ₂ pn junction with ZnS. In this way, the solar light absorption spectral range of the absorbing layer can be increased, and a higher photoelectric conversion efficiency can be realized.

In the present invention, after the CIGS layer is prepared, a CIGSS transition layer is formed through a vulcanization process, thereby improving the ZnS/CIGS interface state.

In the present invention, the back electrode of the battery adopts Mo-Cu alloy instead of Mo, which not only solves the problem of adhesion between the back electrode and the absorption layer, but also has a simple process.

A kind of method for preparing above-mentioned solar cell, it is characterized in that comprising the following steps:

(1) On the surface of the substrate, use Cu, Mo alloy sputtering or use Cu, Mo double target sputtering, deposit Cu-Mo alloy back electrode;

(2) Preparation of the absorbing layer: use the co-evaporation method, that is, use Cu, In, Ga, Se for reaction evaporation, and form copper indium gallium selenide (Cu(In, Ga)Se ₂ ) on the substrate covered with the back electrode film;

(3) Preparation of the transition layer: Evaporate sulfur on the surface of the copper indium gallium selenium thin film or co-evaporate sulfur with at least one of copper, indium, gallium, and selenium to form a prefabricated film containing sulfur, and then through the vacuum heat treatment process, diffuse To form copper indium gallium sulfide selenide film, the heat treatment temperature is 350°C-550°C;

(4) Preparation of ZnS window layer: the electroless plating method is used to make the plating solution contain ammonia and thiourea (NH ₂ CSNH ₂ ), and at least one of Zn halides, nitrates, sulfates, and acetates compound, the temperature of the bath is 60°C-85°C, and the pH of the bath is 10.0-12.0;

(5) After cleaning and drying with argon gas, a transparent electrode is prepared on the surface of the window layer, and then coated with a metal lead; and then an anti-reflection film is prepared to obtain the solar cell of the present invention.

In the above-mentioned preparation step (2), the preparation of the absorbing layer adopts the solid-state selenization method, that is, firstly, a step-by-step sputtering or evaporation method is used to form a preliminary layer containing copper, indium, gallium, and selenium, and the vacuum heat treatment process under the selenium atmosphere , the heat treatment temperature is 350°C-550°C, and the copper indium gallium sulfide selenide film is formed by diffusion.

In the above preparation step (3), the preparation method of the transition layer can also adopt the electroless plating method, and the plating solution contains at least one compound in thial (CH ₃ CSNH ₂ ), hydrochloric acid and indium halides, indium nitrate, and indium sulfate , the solution temperature is 70°C-90°C to form a sulfur-containing prefabricated film, and then diffuse to form a copper indium gallium sulfide selenide film through a vacuum heat treatment process, and the heat treatment temperature is 350°C-550°C;

In the above preparation step (4), the preparation method of the ZnS thin film of the window layer can also adopt the electron beam evaporation method, the evaporation material is ZnS crystal, and the substrate temperature is 250-350°C.

Since the present invention replaces materials such as ZnO with ZnS as the window layer of the thin-film solar cell, the solar light absorption spectrum range of the absorbing layer is increased, and the use of harmful substances containing heavy metal Cd is avoided; the back electrode of the battery in the present invention adopts The Mo-Cu alloy replaces Mo, which makes the combination between the battery and the substrate more firm, and improves the production yield of the battery; the invention forms a CIGSS transition layer through a simple vulcanization process, and improves the working stability of the battery. Therefore, the invention has the advantages of simple battery structure, high light conversion efficiency, good stability, no pollution, simple process and the like.

Description of drawings

FIG. 1 is a schematic cross-sectional view of a solar cell of the present invention.

Fig. 2 is the I-V characteristic curve of the solar cell prepared in Example 5.

Detailed ways

The structure and preferred mode of the solar cell will be described in detail below with reference to the accompanying drawing 1: the substrate 1 used in the solar cell in the present invention can be selected from soda-lime glass or stainless steel. A Cu-Mo alloy back electrode 2 is deposited on its surface. The Cu-Mo alloy layer can be vacuum sputtered, such as Cu-Mo alloy sputtering or Cu, Mo double target sputtering, to deposit a Cu-Mo alloy layer with a thickness of about 0.5-2 μm, which is used as the back electrode of the battery. Its surface is welded with side electrodes 9 . Since the quality of the Cu-Mo alloy substrate directly affects the adhesion of the film and the series resistance of the battery, attention should also be paid to the cleaning of the substrate, and a high degree of vacuum and cleanliness should be maintained during the preparation process to minimize pinholes. The composition content of Cu in the prepared Cu-Mo alloy thin film is 3-30%.

The CIGS absorbing layer 3 can adopt a co-evaporation method, a selenization method or a combination of the two methods. That is, Cu, In, Ga, and Se are used for reactive evaporation to form a Cu (In, Ga) Se ₂ film on the substrate. Or prepare a prefabricated layer containing Cu, In, Ga and Se on the substrate first, and then carry out selenization in a selenium atmosphere, and the selenization temperature is 350-550°C. The film forming method can be evaporation, sputtering, sputtering pyrolysis, close-range sublimation, molecular beam epitaxy, electrodeposition, etc. The film thickness of this layer is 1.0-3.0 μm thick.

The copper indium gallium sulfide selenide (CIGSS) transition layer 4 can be prepared by evaporation or electroless plating. The evaporation method includes the evaporation of sulfur or the co-evaporation of sulfur and at least one material in copper, indium, gallium, and selenium to form a prefabricated film; the electroless plating method includes using In ⁺³ (0.001-0.005M) and CH ₃ For the mixed solution of CSNH ₂ (0.1-0.3M), the pH is adjusted between 1.5-2.8 with hydrochloric acid, and the temperature is 70-90°C to form a sulfur-containing prefabricated layer by electroless plating. The prefabricated films prepared by the above two methods need to be annealed in vacuum at 350-500°C, and protective gases such as argon and nitrogen can also be used. Generation of CIGSS thin films. Its thickness is 30-80nm.

The preparation method of the ZnS window layer 5 may be electroless plating or vacuum evaporation. Among them, electroless plating can choose a plating solution containing Zn ⁺² (0.1-0.3M), ammonia water (5-8M, PH=10.5-11.0), thiourea (NH ₂ CSNH ₂ , 0.3-0.9M), and the temperature is at 60- 85°C, electroless ZnS layer. Among them, the vacuum evaporation method can choose ZnS crystal particles, which can be realized by thermal evaporation or electron beam evaporation. The film thickness is 70-220nm.

The transparent electrode 6 can be selected from zinc aluminum oxide (ZAO) or indium tin oxide (ITO), etc., wherein the preparation method of zinc aluminum oxide can use metal target sputtering, and the zinc aluminum oxide thin film with the best performance is made of zinc aluminum oxide ceramic target Prepared by radio frequency or high frequency AC magnetron sputtering. The thickness of this layer is 0.10-0.35 μm. ITO is generally prepared by magnetron sputtering using ceramic targets.

The upper surface of the transparent electrode layer is coated with metal leads 8, and the material may be gold, silver, aluminum, etc. In order to improve the conversion efficiency of the battery, an anti-reflection film layer 7 is deposited on the upper surface of the battery. The material of the anti-reflection film can be MgF ₂ , CaF ₂ , SiO ₂ and the like.

Example 1:

On the surface of soda-lime glass, a Cu-Mo alloy back electrode was deposited by sputtering with Cu and Mo alloy targets, with a thickness of about 1.45 μm. The content of Cu in the prepared Cu-Mo alloy film was 6%. Then adopt the co-evaporation method, that is, use Cu, In, Ga, and Se for reactive evaporation to form a Cu (In, Ga) Se ₂ film on the substrate, and start to evaporate sulfur when its thickness grows to 2.0 μm. The substrate temperature is 350°C, and the evaporation rate is 6/S. A sulfur-containing preliminary layer was formed with a thickness of about 50 nm. Then, under an argon protective atmosphere, annealing is performed at 500° C. for 15 minutes to form a CIGSS thin film. After cleaning and drying with argon gas, immerse in a solution containing 0.1MZn ⁺² , 7M ammonia water, and 0.6M thiourea at room temperature, take it out after 30 seconds, raise the temperature of the plating solution to 85°C, and repeat the immersion five times to form A dense ZnS film layer with a thickness of about 120nm. Then, after cleaning and drying with argon gas, a transparent electrode ITO was prepared on the surface, and an ITO ceramic target was used to prepare an ITO film with a thickness of 0.12 μm by magnetron sputtering. Aluminum metal leads are covered on the transparent electrodes. A solar cell was produced, the open circuit voltage of the cell was 346mV, and the short circuit current density was 15.2mA/cm ² .

Example 2:

On the surface of soda-lime glass, a Cu-Mo alloy back electrode was deposited by sputtering with Cu and Mo alloy targets, with a thickness of about 1.45 μm. The content of Cu in the prepared Cu-Mo alloy film was 15%. After cleaning and drying with argon gas, a preliminary layer containing Cu, In and Ga was formed on the substrate by magnetron sputtering, and its thickness was 1.2 μm. On its surface, a selenium layer with a thickness of 0.7 μm was evaporated, and kept at 500° C. for 20 minutes in an atmosphere of selenium. Subsequently, co-evaporation of sulfur and indium is carried out. The substrate temperature is 450° C., and after vacuum annealing at 500° C. for 10 minutes, a CIGSS film with a thickness of about 35 nm is formed. Immerse in a solution containing 0.2MZn ⁺² , 6M ammonia water, and 0.8M thiourea at room temperature, take it out after 30 seconds, raise the temperature of the plating solution to 80°C, and repeat the dipping five times to form a dense ZnS film with a thickness of about 110nm layer. Then, after cleaning and drying with argon gas, a transparent electrode ITO was prepared on the surface, and an ITO film with a thickness of 0.21 μm was prepared by using an ITO ceramic target and magnetron sputtering. Aluminum metal leads are covered on the transparent electrodes. A solar cell was produced, the open circuit voltage of the cell was 366mV, and the short circuit current density was 13.1mA/cm ² .

Example 3:

On the surface of soda-lime glass, a Cu-Mo alloy back electrode was deposited by sputtering with Cu and Mo metal targets, with a thickness of about 1.55 μm. The content of Cu in the prepared Cu-Mo alloy film was 3%. After cleaning and drying with argon gas, a preparatory layer of Cu, In, and Ga was formed on the substrate by magnetron sputtering, the thickness of which was 1.2 μm. Then evaporate a selenium layer with a thickness of 0.6 μm, and keep it at 450° C. for 25 minutes in a selenium atmosphere. On the surface of the CIGS film, use the electroless plating method, use a mixed solution containing In ⁺³ 0.004M and CH ₃ CSNH ₂ 0.25M, adjust the pH to 1.8 with hydrochloric acid, and form a sulfur-containing preliminary layer with a thickness of 48nm by electroless plating. After vacuum annealing at 500°C for 13 minutes, immerse in a solution containing 0.4MZn ⁺² , 7M ammonia water, and 0.5M thiourea at room temperature, take it out after 30 seconds, raise the temperature of the plating solution to 75°C, and repeat the dipping seven times , forming a dense ZnS film layer with a thickness of about 110nm. Then, after cleaning and drying with argon gas, a transparent electrode ZAO was prepared on the surface, and a ZAO thin film with a thickness of 0.25 μm was prepared by using a ZAO ceramic target and magnetron sputtering. Aluminum metal leads are covered on the transparent electrodes. A solar cell was produced, the open circuit voltage of the cell was 423mV, and the short circuit current density was 10.6mA/cm ² .

Example 4:

On the surface of soda-lime glass, a Cu-Mo alloy back electrode was deposited by sputtering with Cu and Mo metal targets, with a thickness of about 1.5 μm. The content of Cu in the prepared Cu-Mo alloy film was 28%. Then, a co-evaporation method is used, that is, Cu, In, Ga, and Se are used for reactive evaporation to form a Cu(In, Ga)Se ₂ film on the substrate with a thickness of 2.3 μm. On the surface of the CIGS film, the electroless plating method is used to form a sulfur-containing prefabricated layer by electroless plating with a mixed solution containing In ⁺³ 0.002M and CH ₃ CSNH ₂ 0.15M, and hydrochloric acid at a pH value of 2.0. Then at 450°C, vacuum annealing produces a CIGSS film with a thickness of about 60nm. Subsequently, a ZnS layer was prepared on it by electron beam evaporation method, using ZnS crystal particles with a particle size of about 100mm ³ , the substrate temperature was 200°C, and the ZnS film thickness reached 150nm after evaporation for 120 seconds. The transparent electrode ZAO uses a zinc-aluminum oxide ceramic target, high-frequency AC magnetron sputtering. The thickness is 0.35 μm. Aluminum metal leads are covered on the transparent electrode layer. Then evaporate a layer of magnesium fluoride film with a thickness of about 150nm as an anti-reflection film for light. A solar cell was produced, the open circuit voltage of the cell was 418mV, and the short circuit current density was 12.7mA/cm ² .

Example 5:

On the surface of soda-lime glass, a molybdenum-copper alloy back electrode layer containing 20% copper was deposited by sputtering with a Cu-Mo alloy target, with a thickness of about 1.5 μm. A preliminary layer of Cu, In, and Ga was formed on the substrate to have a thickness of 1.3 µm. Subsequently, a selenium layer with a thickness of 0.5 μm was evaporated, and selenized in a nitrogen protective atmosphere at 530° C. for 25 minutes to form a CIGS thin film layer. Then, by evaporation method, co-evaporation of sulfur, selenium, indium and copper is carried out. The substrate temperature is 380°C, evaporated for 20 seconds to form a sulfur-containing transition layer film with a thickness of 30nm, and then vacuum annealed at 400°C for 20 minutes to form a CIGSS film. Then the ZnS layer was prepared by electron beam evaporation method, using ZnS crystal particles with a particle size of about 150mm ³ , the substrate temperature was 250°C, and the evaporation rate was 3/S to form a ZnS thin film layer with a thickness of 120nm. The transparent electrode ZAO uses a zinc-aluminum oxide ceramic target, high-frequency AC magnetron sputtering. The thickness is 0.12 μm. Aluminum metal leads are covered on the transparent electrode layer. Then evaporate a layer of magnesium fluoride film with a thickness of about 110nm as an anti-reflection film for light. Made into solar cells. Its IV characteristic curve is shown in Figure 2.

Claims (8)

1. a copper-indium-galliun-selenium film solar cell is made up of antireflective coating, transparent electrode layer, Window layer, transition zone, light absorbing zone, metal back electrode and substrate successively, it is characterized in that: described Window layer is n type zinc sulphide (ZnS) film.

2. solar cell as claimed in claim 1 is characterized in that: described light absorbing zone is Copper Indium Gallium Selenide (Cu (In, Ga) Se ₂) the P type semiconductor film.

3. according to claim 1 or 2 described solar cells, it is characterized in that: described transition zone be copper indium gallium sulphur selenium (Cu (and In, Ga) (S, Se) ₂) film.

4. according to the described solar cell of claim 3, it is characterized in that: described metal back electrode is molybdenum-copper alloy (Mo-Cu), and wherein the content of copper is 3～30%.

5. one kind prepares the method for solar cell according to claim 1, and its feature may further comprise the steps:

(1) on the surface of substrate,, deposits Cu-Mo alloy back electrode with Cu, Mo alloy sputter or with Cu, Mo dual-target sputtering;

(2) preparation of absorbed layer: use coevaporation method, promptly carry out reactive evaporation, form Copper Indium Gallium Selenide (Cu (In, Ga) Se on the substrate of back electrode being covered with Cu, In, Ga, Se ₂) film;

(3) preparation of transition zone: at least a material co-evaporated in CIGS thin-film surface evaporation sulphur or sulphur and copper, indium, gallium, selenium, generate the prefabricated membrane of sulfur-bearing, by the vacuum heat process, diffuse to form copper indium gallium sulphur selenium film then, heat treatment temperature is 350 ℃-550 ℃;

(4) preparation ZnS Window layer: adopt chemical plating method, make and contain ammoniacal liquor and thiocarbamide (NH in the plating bath ₂CSNH ₂), and contain at least a compound in the halide, nitrate, sulfate, acetate of Zn, and bath temperature is at 60 ℃-85 ℃, and the pH value of plating bath is 10.0-12.0;

(5) dry up through cleaning, argon gas, in Window layer surface preparation transparency electrode, coated metal goes between again; Prepare antireflective coating then, promptly make solar cell of the present invention.

6. according to the described preparation method of claim 5, it is characterized in that: solid-state selenizing method is adopted in the preparation of step (2) absorbed layer, promptly at first adopt the method for substep sputter or evaporation to form the preparation layers of cupric, indium, gallium, selenium, by the vacuum heat process under the selenium atmosphere, heat treatment temperature is 350 ℃-550 ℃, diffuses to form copper indium gallium sulphur selenium film.

7. according to the described preparation method of claim 5, it is characterized in that: chemical plating method is adopted in the preparation of step (3) transition zone, and its plating bath contains thioaldehydes (CH ₃CSNH ₂), at least a compound in the halide of hydrochloric acid and indium, indium nitrate, indium sulfate, solution temperature is 70 ℃-90 ℃, generates the prefabricated membrane of sulfur-bearing, then by the vacuum heat process, diffuse to form copper indium gallium sulphur selenium film, heat treatment temperature is 350 ℃-550 ℃;

8. according to the described preparation method of claim 5, it is characterized in that: the preparation of step (4) Window layer zinc sulphide (ZnS) film can be adopted electron beam evaporation method, and evaporating materials is a zinc sulfide crystal, and base reservoir temperature is 250-350 ℃.

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