CN105870210A - CIGS/CGS double-junction laminated thin film solar cell - Google Patents

Abstract

The invention relates to a CIGS/CGS double-junction laminated thin-film solar cell, comprising a narrow-bandgap copper-indium-gallium-selenium bottom cell and a wide-bandgap copper-gallium-selenide top cell, characterized in that: the bottom cell and the top cell are composed of The inside of the connection layer is connected in series; the connection layer is composed of a transparent metal oxide conductive layer located at the bottom cell and a nano-metal conductive layer located at the top cell; the conductive window layer of the copper gallium selenide top cell includes an ITO composite conductive film layer and an ITO thin film layer, the surface of the conductive window layer and the electrode layer of the copper gallium selenide top battery has a silicon nitride anti-reflection layer. The present invention adopts the combination of transparent metal oxide and nano-metal thin film as the connection layer between the bottom cell and the top cell, solves the problem of process compatibility between the bottom cell and the top cell, and realizes the internal connection between the bottom cell and the top cell The electrical connection simplifies the battery manufacturing process, reduces the battery manufacturing cost, the battery structure is simple, and the conductive window layer has high light transmittance and electrical conductivity and good passivation effect, and the series resistance is small, which effectively improves the photoelectric conversion of thin film solar cells efficiency.

Description

A CIGS/CGS Double Junction Laminated Thin Film Solar Cell

technical field

The invention belongs to the technical field of thin film solar cells, in particular to a CIGS/CGS double-junction laminated thin film solar cell.

Background technique

At present, the solar cells used in the market are still dominated by the first-generation monocrystalline silicon/polycrystalline silicon cells, but the second-generation thin-film solar cells are recognized as the main direction of solar cell development in the future. Thin-film solar cells refer to solar cells made of materials with a thickness on the order of microns, which is one of the most effective ways to greatly reduce the cost of solar cells. Among many thin-film solar cells, I-III-VI compound semiconductor copper indium (gallium) selenium thin-film solar cells (also known as Cu(In,Ga)Se2 (referred to as CIGS) thin-film solar cells) are known for their high conversion efficiency and long-term stability. The advantages of good performance and strong radiation resistance have become a research hotspot in the photovoltaic industry, and it is expected to become the next generation of cheap solar cells. Regardless of the generation of solar cells, there is a limit of energy conversion rate (31%). Shockley and Queisser analyzed the reasons for the existence of the limit of conversion rate: (1) when photons with energy higher than the band gap generate carriers, the The excess energy of the flow is lost in the form of phonon emission; (2) Photons with energy lower than the band gap are not absorbed. One of the ways to solve this problem is to broaden the absorption range of photovoltaic materials for solar spectral energy, such as using multi-junction stacks or multi-bandgap structures, split energy absorption or realize multi-photon absorption.

The concept of stacked solar cells was first proposed by Jackson in 1955. At present, the efficiency of triple-junction GaAs solar cells has exceeded 40%, which is much higher than that of traditional single-junction cells. Stacked solar cells have been successfully applied to the preparation of cells made of different materials. The most mature technology is the III-V compound multi-junction cell represented by GaAs, such as the GaInP/GaInAs/Ge triple-junction cell connected by a tunnel junction at 454 times The conversion efficiency under light conditions has reached 41.1%, which is currently the most efficient solar cell. In addition, research on thin-film stacked solar cells has also attracted widespread attention. The basic structure of the triple-junction amorphous silicon stacked solar cells is α-Si/α-SiGe/α-SiGe. A more efficient tandem solar cell can be obtained by hydrogenating amorphous silicon and amorphous silicon germanium. Its structure is α-Si:H/α-SiGe:H/α-SiGe:H, which has achieved 15.39% conversion efficiency.

Since the optical band gap can be effectively adjusted by using the distribution ratio, the I-III-VI chalcopyrite compound semiconductor has unique advantages in the field of tandem solar cells. In the I-III-VI compound semiconductor system, the optical bandgap of the Cu-based chalcopyrite compound is 0.9-2.9eV, and the bandgap of the Ag-based chalcopyrite compound is 0.6-3.1eV. Such a wide optical bandgap range is in There is great potential in the application of tandem solar cells.

The entire structure of the existing thin-film stacked solar cells is connected in series by multiple tunnel junctions. As a result, the entire cell structure has only two contacts or "two ends". In order to obtain high-efficiency polycrystalline thin-film tandem solar cells, the top cell must have a wide bandgap semiconductor material, and a transparent conductive material as the back contact. Because of this, it becomes imperative to use transparent conductive oxides as the back contact. Currently known I-III-VI chalcopyrite compound semiconductor double-junction thin-film solar cells have realized that the top cell adopts a wide bandgap semiconductor material and a transparent conductive oxide as the back contact, which improves the conversion efficiency of the solar cell, but due to the I- The III-VI chalcopyrite compound cannot realize the tunnel junction, the process compatibility between the bottom cell and the top cell is poor, and the direct internal connection between the bottom cell and the top cell cannot be directly connected, and the external cascading method is often used. As a result, the entire cell needs three One or four contacts make the structure of the battery complex and increase the manufacturing cost of the battery.

Contents of the invention

The invention provides a CIGS/CGS double-junction stacked thin film solar cell with simple structure, low manufacturing cost and high cell conversion efficiency to solve the technical problems in the known technology.

The following technical solutions of the present invention are:

A CIGS/CGS double-junction laminated thin-film solar cell, comprising a narrow-bandgap copper-indium-gallium-selenide bottom cell and a wide-bandgap copper-gallium-selenide top cell, is characterized in that: the bottom cell and the top cell are formed by a connecting layer inside connected in series; the connecting layer is composed of a transparent metal oxide conductive layer positioned at the bottom cell and a nano-metal conductive layer positioned at the top cell; the conductive window layer of the copper-gallium-selenide top cell includes an ITO composite conductive film layer and an ITO film Layer, the surface of the conductive window layer and the electrode layer of the copper gallium selenide top battery has a silicon nitride anti-reflection layer.

The present invention can also adopt following technical measures:

The transparent metal oxide conductive layer is one of the TCO thin films formed by Al, Ga or In doped ZnO with a thickness of 300-600nm, or an ITO thin film; the nano-metal conductive layer is a Mo thin film with a thickness of 30-50nm.

The narrow-bandgap copper indium gallium selenide bottom cell includes from bottom to top a 600nm-800nm thick Mo film as the back electrode Mo1, a 1.5-2.0μm thick CIGS film as the bottom cell p-type absorption layer, and a 30-50nm n-type CdS The copper indium gallium selenium and cadmium sulfide heterojunction battery composed of the thin film as the n-type buffer layer of the bottom cell and the intrinsic zinc oxide thin film bottom cell intrinsic window layer of 50-60nm.

The copper-gallium-selenium top cell with wide bandgap includes from bottom to top a 1-1.5 μm thick CGS film as the top cell p-type absorption layer, a 30-50 nm thick n-type CdS film as the top cell n-type buffer layer, and a 50-60 nm thick film as the top cell n-type buffer layer. Copper gallium selenide and cadmium sulfide isotope composed of thick intrinsic ZnO film as the intrinsic window layer of the top cell, conductive window layer of the top cell, 2-4 μm thick Al as the electrode layer, and 100-200 nm thick silicon nitride anti-reflection layer A mass junction battery, wherein the conductive window layer of the top battery includes a 10-30nm thick ITO composite conductive thin film layer and a 30-80nm thick ITO thin film layer.

The molar ratio of ITO:silicon dioxide:silicon nitride in the ITO composite conductive film layer is 1:0.01-0.3:0.01-0.3.

The advantages and positive effects that the present invention has:

The invention solves the process compatibility problem between the bottom battery and the top battery by using the combination of transparent metal oxide and nanometer metal thin film as the connection layer between the bottom battery and the top battery, and realizes the internal electrical connection between the bottom battery and the top battery. The connection simplifies the battery production process, reduces the production cost of the battery, and the battery structure is simple; the invention uses ultra-thin nano-metal Mo to transition between the transparent metal oxide and the top battery absorption layer, which solves the problem of direct contact between the two. The anti-junction phenomenon caused by the Mo thin film is beneficial to the advantages of growing I-III-VI group materials; the top cell absorber layer of the present invention adopts a low-temperature process deposition method, which effectively reduces the impact of the top cell preparation process on the performance of the bottom cell; The light transmittance and electrical conductivity of the conductive window layer of the top cell of the present invention are high, the passivation effect is good, the series resistance is small, and the presence of the silicon nitride anti-reflection layer effectively improves light absorption, thereby effectively improving the photoelectricity of the thin film solar cell. conversion efficiency.

Description of drawings

Fig. 1 is a schematic structural diagram of a CIGS/CGS double-junction laminated thin film solar cell prepared by the present invention.

The labels in the figure are: 1-back electrode Mo; 2-bottom cell p-type absorber layer; 3-bottom cell n-type buffer layer; 4-bottom cell intrinsic window layer; 5-connection layer; 6-top cell p 7-top cell n-type buffer layer; 8-top cell intrinsic window layer; 9-top cell conductive window layer; 10-electrode layer; 11-silicon nitride anti-reflection layer.

detailed description

In order to further disclose the invention content, features and effects of the present invention, the following examples are specifically cited and described in detail in conjunction with the accompanying drawings as follows.

A CIGS/CGS double-junction stacked thin-film solar cell includes a narrow bandgap copper indium gallium selenide bottom cell and a wide band gap copper gallium selenide top cell.

The innovation point of the present invention is:

The bottom cell and the top cell are integrated in series by the connection layer 5; the connection layer is composed of a transparent metal oxide conductive layer positioned at the bottom cell and a nano-metal conductive layer positioned at the top cell, and the copper gallium selenide top cell The conductive window layer 9 includes an ITO composite conductive thin film layer and an ITO thin film layer, and the surface of the conductive window layer and the electrode layer of the copper gallium selenide top battery has a silicon nitride anti-reflection layer 11; the transparent metal oxide conductive layer is 300 -One of the TCO films formed by Al, Ga or In doped ZnO with a thickness of 600nm, or an ITO film; the nano-metal conductive layer is a Mo film with a thickness of 30-50nm; the copper indium gallium selenide bottom cell with a narrow bandgap From bottom to top, it includes a 600nm-800nm thick Mo film as the back electrode Mo1, a 1.5-2.0 μm thick CIGS film as the bottom cell p-type absorber layer 2, and a 30-50nm n-type CdS film as the bottom cell n-type buffer layer 3 and A copper indium gallium selenide and cadmium sulfide heterojunction cell composed of a 50-60nm thick intrinsic zinc oxide thin film bottom cell intrinsic window layer 4; The CGS thin film is used as the top cell p-type absorption layer 6, the 30-50nm thick n-type CdS film is used as the top cell n-type buffer layer 7, the 50-60nm thick intrinsic ZnO thin film is used as the top cell intrinsic window layer 8, the top cell Copper gallium selenide and cadmium sulfide heterojunction cell composed of conductive window layer 9 and 2-4 μm thick Al as electrode layer 10 and 100-200 nm thick silicon nitride anti-reflection layer 11, wherein the top cell conductive window layer 9 Including a 10-30nm thick ITO composite conductive film layer and a 30-80nm thick ITO film layer; in the ITO composite conductive film layer, the molar ratio of ITO: silicon dioxide: silicon nitride is 1: 0.01～0.3: 0.01～ 0.3.

A preparation process of a CIGS/CGS double-junction laminated thin-film solar cell:

Step 1: Prepare the back electrode Mo on the substrate by DC magnetron sputtering:

(1) At room temperature, first use a background vacuum of <5×10-3Pa, a high pressure of 1-2Pa, and a low sputtering power of 60W, and DC magnetron sputtering on a flexible polyimide substrate Deposit Mo, the deposition time is 60min, and the first layer of Mo film with a thickness of 0.05-0.1μm is formed on the substrate;

(2) Deposit Mo on the first layer of Mo film by direct current magnetron sputtering using a background vacuum of <5×10-3Pa, a working pressure of 0.2-0.4Pa, a low pressure of 0.2-0.4Pa, and a high sputtering power of 150W. For 150min, form the second layer of Mo film, and the two-layer Mo film forms a double-layer Mo film with a total thickness of 600-800nm as the back electrode Mo1;

Step 2: Prepare the bottom cell p-type absorber layer on the back electrode Mo in three steps:

(1) The first step: the substrate temperature is heated to 380-400°C, and 90% of In, Ga and Se elements are evaporated on the back electrode Mo to form a (In0.7Ga0.3)2Se3 pre-layer, Se/(In+ Ga) The flow rate ratio is greater than 3, and the temperature of each evaporation source is set as follows: TIn=810°C, TGa=850°C, TSe=240°C, and the evaporation time is 12-15min;

(2) The second step: raise the substrate temperature to 450-550°C, evaporate Cu and Se elements on the preset layer, and set the temperature of each evaporation source as follows: TCu=1050°C, TSe=240°C until the cooling point appears End the evaporation of Cu;

(3) The third step: keep the substrate temperature at 450-550°C, evaporate In, Ga and Se elements, and set the temperature of each evaporation source as follows: TIn=810°C, TGa=850°C, TSe=240°C, and the evaporation time is 2-3min; form a 1.5-2.0μm thick narrow bandgap CIGS thin film on the back electrode Mo as the p-type absorber layer 2 of the bottom cell;

Step 3: Prepare the bottom cell n-type buffer layer on the bottom cell p-type absorber layer by chemical bath method (CBD): select (CH3COO)2Cd=0.001M, SC(NH2)2=0.01M, CH3COONH4=0.03M, NH4OH= 0.003M to prepare the reaction solution; adjust the pH value of the reaction solution to 8-9, the water bath temperature is 60°C-70°C, the water bath time is 30min, and grow 30-50nm thick n-type CdS on the p-type absorption layer of the bottom cell Thin film as bottom cell n-type buffer layer 3;

Step 4: Prepare the intrinsic window layer of the bottom cell on the n-type buffer layer of the bottom cell by radio frequency magnetron sputtering:

Set the background vacuum to <8×10-4Pa, adjust the O2:Ar ratio to 80:1, the working pressure to 0.7-0.8Pa, the sputtering power density to 2.0-2.5W/cm2, and the sputtering time to 20-40min; RF magnetron sputtering 50-60nm thick intrinsic ZnO film on the n-type buffer layer of the bottom cell as the intrinsic window layer 4 of the bottom cell;

Step 5: Prepare a connection layer on the intrinsic window layer of the bottom cell by radio frequency magnetron sputtering:

(1) Preparation of a transparent metal oxide conductive layer on the intrinsic window layer of the bottom cell

The background vacuum is <8×10-4Pa, the working pressure is 0.4-0.6Pa, the sputtering power density is 2.5-2.8W/cm2, the sputtering time is 100-150min, and the RF magnetron is on the intrinsic window layer of the bottom battery Al-doped ZnO film is sputtered, and a ZAO film with a thickness of 300-600nm is formed on the intrinsic window layer of the bottom cell as a transparent metal oxide conductive layer;

⑵Development of metal oxide conductive layer to prepare nano-metal conductive layer

The background vacuum is <5×10-3Pa, the working pressure is 0.2-0.8Pa, the sputtering power is 120-130W, the sputtering time is 10min, and the Mo film with a thickness of 30-50nm is sputtered on the ZAO film by RF magnetron sputtering As a nano-metal conductive layer;

The transparent metal oxide conductive layer and the nano-metal conductive layer constitute the connection layer 5 between the bottom cell and the top cell;

Step 6: Prepare the top cell p-type absorber layer on the connection layer in three steps:

(1) Step 1: Evaporate Ga2Se3 preset layer on the Mo film of the connection layer. When the substrate temperature is 380±10°C, TGa=850°C, TSe=240°C, evaporate 90% of Ga and Se elements on the Mo film, and the evaporation time For 10-12min, the Se/(In+Ga) flow ratio is greater than 3, and a Ga2Se3 preset layer is formed on the Mo film;

(2) The second step: raise the substrate temperature to 450±10°C, TCu=1050°C, TSe=240°C, evaporate Cu and Se elements on the Ga2Se3 preset layer, and the evaporation time is 8-10min;

(3) The third step: keep the substrate temperature at 450±10°C, TGa=850°C, TSe=240°C, evaporate Ga and Se elements on the basis of the second step, and the evaporation time is 2-3min; co-evaporate on the Mo film Produce a 1-1.5 μm wide bandgap CGS thin film as the top cell p-type absorber layer 6;

Step 7: Prepare the n-type buffer layer of the top cell on the p-type absorber layer of the top cell by chemical bath method: select (CH3COO)2Cd=0.001M, SC(NH2)2=0.01M, CH3COONH4=0.03M, NH4OH=0.003M to prepare into a reaction solution; adjust the pH value of the reaction solution to 8-9, the water bath temperature is 60°C-70°C, and the water bath time is 30min, grow a 30-50nm n-type CdS film on the p-type absorption layer of the top cell as the top cell n-type buffer layer 7;

Step 8: Prepare the intrinsic window layer of the top cell on the n-type buffer layer of the top cell by radio frequency magnetron sputtering method:

Set the background vacuum to <8×10-4Pa, adjust the O2:Ar ratio to 80:1, the working pressure to 0.8Pa, the sputtering power density to 2.0-2.5W/cm2, and the sputtering time to 25-35min; The ZnO thin film with a thickness of 50-60 nm is used as the intrinsic window layer 8 of the top battery by RF magnetron sputtering on the n-type buffer layer of the battery;

Step 9: Prepare the conductive window layer of the top cell on the intrinsic window layer of the top cell by radio frequency magnetron sputtering:

Set the background vacuum to <8×10-4Pa, the working pressure to 0.4-0.6Pa, the sputtering power density to 2.5-2.8W/cm2, and the sputtering time to 120-150min. Controlled sputtering 10-30nm thick ITO composite conductive thin film layer and 30-80nm thick ITO thin film layer are used as top cell conductive window layer 9, wherein in the ITO composite conductive thin film layer, ITO: silicon dioxide: the mole of silicon nitride The ratio is 1:0.01～0.3:0.01～0.3;

Step 10: Prepare the electrode layer on the conductive window layer of the top cell by DC magnetron sputtering method:

Set the background vacuum to <5×10-3Pa, the working pressure to 0.6Pa, the sputtering power density to 2W/cm2, the sputtering time to 50-80min, and the thickness of DC magnetron sputtering on the conductive window layer of the top battery to be 2 - 4 μm of Al as electrode layer 10;

Step 11: Deposit the silicon nitride anti-reflection layer 11 on the surface of the conductive window layer and the electrode layer by PECVD method, that is, complete the CIGS/CdS heterojunction bottom cell made from step 1-step 4 of the connection layer as shown in Figure 1 A double-junction laminated thin-film solar cell integrated in series with the inside of the CGS/CdS heterojunction top cell made in steps 6-10.

Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are only illustrative and not restrictive. Those of ordinary skill in the art Under the enlightenment of the present invention, personnel can also make many forms without departing from the purpose of the present invention and the scope protected by the claims. These all belong to the scope of protection of the present invention.

Claims (5)

1. A CIGS/CGS double-junction stacked thin film solar cell, comprising a narrow bandgap copper indium gallium selenide bottom cell and a wide band gap copper gallium selenide top cell, characterized in that: the bottom cell and the top cell are connected by The inside of the layer is connected in series; the connecting layer is composed of a transparent metal oxide conductive layer positioned at the bottom cell and a nano-metal conductive layer positioned at the top cell; the conductive window layer of the copper gallium selenide top cell includes an ITO composite conductive film layer and ITO film layer, the surface of the conductive window layer and the electrode layer of the copper gallium selenide top battery has a silicon nitride anti-reflection layer. 2. A kind of CIGS/CGS double-junction laminated thin-film solar cell according to claim 1, characterized in that: the transparent metal oxide conductive layer is formed of 300-600nm thick Al, Ga or In-doped ZnO One of TCO thin films, or ITO thin films; the nano metal conductive layer is a Mo thin film with a thickness of 30-50nm. 3. A CIGS/CGS double-junction laminated thin-film solar cell according to claim 1, characterized in that: the narrow-bandgap copper indium gallium selenide bottom cell comprises a 600nm-800nm thick Mo thin film from bottom to top as the back Electrode Mo1, 1.5-2.0μm thick CIGS thin film as bottom cell p-type absorber layer, 30-50nm n-type CdS thin film as bottom cell n-type buffer layer and 50-60nm thick intrinsic ZnO thin film bottom cell intrinsic window Copper indium gallium selenide and cadmium sulfide heterojunction cells composed of layers. 4. A CIGS/CGS double-junction laminated thin-film solar cell according to claim 1, characterized in that: the wide-bandgap copper-gallium-selenide top cell includes a 1-1.5 μm thick CGS film as the top from bottom to top. The p-type absorption layer of the battery, the n-type CdS film of 30-50nm thick as the n-type buffer layer of the top battery, the intrinsic ZnO film of 50-60nm as the intrinsic window layer of the top battery, the conductive window layer of the top battery and the 2-4μm thick Copper gallium selenide and cadmium sulfide heterojunction cell composed of Al as electrode layer and 100-200nm thick silicon nitride anti-reflection layer, wherein the top cell conductive window layer includes 10-30nm thick ITO composite conductive film layer and 30-80nm thick ITO film layer. 5. a kind of CIGS/CGS double-junction laminated thin-film solar cell according to claim 4 is characterized in that: ITO in the described ITO composite conductive film layer: silicon dioxide: the mol ratio of silicon nitride is 1: 0.01 ~0.3: 0.01~0.3.