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Copper indium gallium selenide solar cell
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Copper indium gallium selenide solar cell
A copper indium gallium selenide solar cell (CIGS cell, sometimes CI(G)S or CIS cell) is a thin-film solar cell used to convert sunlight into electric power. It is manufactured by depositing a thin layer of copper indium gallium selenide solid solution on glass or plastic backing, along with electrodes on the front and back to collect electric current. Because the material has a high absorption coefficient and strongly absorbs sunlight, a much thinner film is required than of other semiconductor materials.
CIGS is one of three mainstream thin-film photovoltaic (PV) technologies, the other two being cadmium telluride and amorphous silicon. Like these materials, CIGS layers are thin enough to be flexible, allowing them to be deposited on flexible substrates. However, as all of these technologies normally use high-temperature deposition techniques, the best performance normally comes from cells deposited on glass, even though advances in low-temperature deposition of CIGS cells have erased much of this performance difference. CIGS outperforms polysilicon at the cell level, however its module efficiency is still lower, due to a less mature upscaling.
Thin-film market share is stagnated at around 15 percent, leaving the rest of the PV market to conventional solar cells made of crystalline silicon. In 2013, the market share of CIGS alone was about 2 percent and all thin-film technologies combined fell below 10 percent. CIGS cells continue being developed, as they promise to reach silicon-like efficiencies, while maintaining their low costs, as is typical for thin-film technology. Prominent manufacturers of CIGS photovoltaics were the later bankrupted companies Nanosolar and Solyndra. The market leader is the Japanese company Solar Frontier, with Global Solar and GSHK Solar also producing solar modules free of any heavy metals such as cadmium and/or lead. Many CIGS solar panel manufacturer companies have gone bankrupt.
CIGS is a I-III-VI2 compound semiconductor material composed of copper, indium, gallium, and selenium. The material is a solid solution of copper indium selenide (often abbreviated "CIS") and copper gallium selenide, with a chemical formula of CuInxGa(1−x)Se2, where the value of x can vary from 1 (pure copper indium selenide) to 0 (pure copper gallium selenide). It is a tetrahedrally bonded semiconductor, with the chalcopyrite crystal structure. The bandgap varies continuously with x from about 1.0 eV (for copper indium selenide) to about 1.7 eV (for copper gallium selenide).
CIGS has an exceptionally high absorption coefficient of more than 105/cm for 1.5 eV and higher energy photons. CIGS solar cells with efficiencies around 20% have been claimed by the National Renewable Energy Laboratory (NREL), the Swiss Federal Laboratories for Materials Science and Technology (Empa), and the German Zentrum für Sonnenenergie und Wasserstoff Forschung (ZSW) (translated: Center for Solar Energy and Hydrogen Research), which is the record to date for any thin film solar cell. In 2024 a CIGS efficiency record of 23.64% was claimed.
All high performance CIGS absorbers in solar cells have similarities independent of production technique. First, they are polycrystalline α-phase which has the chalcopyrite crystal structure shown in Figure 3. The second property is an overall Cu deficiency. Cu deficiency increases the majority carrier (hole) concentration by increasing the number of (electron-accepting) Cu vacancies. When CIGS films are In rich (Cu deficient) the film's surface layer forms an ordered defect compound (ODC) with a stoichiometry of Cu(In,Ga)
3Se
5. The ODC is n-type, forming a p-n homojunction in the film at the interface between the α phase and the ODC. The recombination velocity at the CIGS/CdS interface is decreased by the homojunction's presence. The drop in interface recombination attributable to ODC formation is demonstrated by experiments which have shown that recombination in the bulk of the film is the main loss mechanism in Cu deficient films, while in Cu rich films the main loss is at the CIGS/CdS interface.
Sodium incorporation is necessary for optimal performance. Ideal Na concentration is considered to be approximately 0.1%. Na is commonly supplied by the soda-lime glass substrate, but in processes that do not use this substrate the Na must be deliberately added. Na's beneficial effects include increases in p-type conductivity, texture, and average grain size. Furthermore, Na incorporation allows for performance to be maintained over larger stoichiometric deviations. Simulations have predicted that Na on an In site creates a shallow acceptor level and that Na serves to remove In on Cu defects (donors), but reasons for these benefits are controversial. Na is also credited with catalyzing oxygen absorption. Oxygen passivates Se vacancies that act as compensating donors and recombination centers.
Alloying CIS (CuInSe2) with CGS (CuGaSe2) increases the bandgap. To reach the ideal bandgap for a single junction solar cell, 1.5 eV, a Ga/(In+Ga) ratio of roughly 0.7 is optimal. However, at ratios above ~0.3, device performance drops off. Industry currently targets the 0.3 Ga/(In+Ga) ratio, resulting in bandgaps between 1.1 and 1.2 eV. The decreasing performance has been postulated to be a result of CGS not forming the ODC, which is necessary for a good interface with CdS.
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Copper indium gallium selenide solar cell
A copper indium gallium selenide solar cell (CIGS cell, sometimes CI(G)S or CIS cell) is a thin-film solar cell used to convert sunlight into electric power. It is manufactured by depositing a thin layer of copper indium gallium selenide solid solution on glass or plastic backing, along with electrodes on the front and back to collect electric current. Because the material has a high absorption coefficient and strongly absorbs sunlight, a much thinner film is required than of other semiconductor materials.
CIGS is one of three mainstream thin-film photovoltaic (PV) technologies, the other two being cadmium telluride and amorphous silicon. Like these materials, CIGS layers are thin enough to be flexible, allowing them to be deposited on flexible substrates. However, as all of these technologies normally use high-temperature deposition techniques, the best performance normally comes from cells deposited on glass, even though advances in low-temperature deposition of CIGS cells have erased much of this performance difference. CIGS outperforms polysilicon at the cell level, however its module efficiency is still lower, due to a less mature upscaling.
Thin-film market share is stagnated at around 15 percent, leaving the rest of the PV market to conventional solar cells made of crystalline silicon. In 2013, the market share of CIGS alone was about 2 percent and all thin-film technologies combined fell below 10 percent. CIGS cells continue being developed, as they promise to reach silicon-like efficiencies, while maintaining their low costs, as is typical for thin-film technology. Prominent manufacturers of CIGS photovoltaics were the later bankrupted companies Nanosolar and Solyndra. The market leader is the Japanese company Solar Frontier, with Global Solar and GSHK Solar also producing solar modules free of any heavy metals such as cadmium and/or lead. Many CIGS solar panel manufacturer companies have gone bankrupt.
CIGS is a I-III-VI2 compound semiconductor material composed of copper, indium, gallium, and selenium. The material is a solid solution of copper indium selenide (often abbreviated "CIS") and copper gallium selenide, with a chemical formula of CuInxGa(1−x)Se2, where the value of x can vary from 1 (pure copper indium selenide) to 0 (pure copper gallium selenide). It is a tetrahedrally bonded semiconductor, with the chalcopyrite crystal structure. The bandgap varies continuously with x from about 1.0 eV (for copper indium selenide) to about 1.7 eV (for copper gallium selenide).
CIGS has an exceptionally high absorption coefficient of more than 105/cm for 1.5 eV and higher energy photons. CIGS solar cells with efficiencies around 20% have been claimed by the National Renewable Energy Laboratory (NREL), the Swiss Federal Laboratories for Materials Science and Technology (Empa), and the German Zentrum für Sonnenenergie und Wasserstoff Forschung (ZSW) (translated: Center for Solar Energy and Hydrogen Research), which is the record to date for any thin film solar cell. In 2024 a CIGS efficiency record of 23.64% was claimed.
All high performance CIGS absorbers in solar cells have similarities independent of production technique. First, they are polycrystalline α-phase which has the chalcopyrite crystal structure shown in Figure 3. The second property is an overall Cu deficiency. Cu deficiency increases the majority carrier (hole) concentration by increasing the number of (electron-accepting) Cu vacancies. When CIGS films are In rich (Cu deficient) the film's surface layer forms an ordered defect compound (ODC) with a stoichiometry of Cu(In,Ga)
3Se
5. The ODC is n-type, forming a p-n homojunction in the film at the interface between the α phase and the ODC. The recombination velocity at the CIGS/CdS interface is decreased by the homojunction's presence. The drop in interface recombination attributable to ODC formation is demonstrated by experiments which have shown that recombination in the bulk of the film is the main loss mechanism in Cu deficient films, while in Cu rich films the main loss is at the CIGS/CdS interface.
Sodium incorporation is necessary for optimal performance. Ideal Na concentration is considered to be approximately 0.1%. Na is commonly supplied by the soda-lime glass substrate, but in processes that do not use this substrate the Na must be deliberately added. Na's beneficial effects include increases in p-type conductivity, texture, and average grain size. Furthermore, Na incorporation allows for performance to be maintained over larger stoichiometric deviations. Simulations have predicted that Na on an In site creates a shallow acceptor level and that Na serves to remove In on Cu defects (donors), but reasons for these benefits are controversial. Na is also credited with catalyzing oxygen absorption. Oxygen passivates Se vacancies that act as compensating donors and recombination centers.
Alloying CIS (CuInSe2) with CGS (CuGaSe2) increases the bandgap. To reach the ideal bandgap for a single junction solar cell, 1.5 eV, a Ga/(In+Ga) ratio of roughly 0.7 is optimal. However, at ratios above ~0.3, device performance drops off. Industry currently targets the 0.3 Ga/(In+Ga) ratio, resulting in bandgaps between 1.1 and 1.2 eV. The decreasing performance has been postulated to be a result of CGS not forming the ODC, which is necessary for a good interface with CdS.
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