1. Cadmium telluride thin film solar Batteries
CdTe is a compound semiconductor with Eg of 1.45 eV. CdTe has become a new type of thin-film solar Battery material with good application prospects because of its high light absorption ability and the large-area deposition of CdTe films. However, due to the self-compensation effect of CdTe, it is difficult to prepare a high-conductivity homojunction, so the actual batteries are mostly heterojunction thin-film batteries. CDs and CdTe have little difference in lattice constants and are usually the best window materials used in CdTe thin film batteries. The preparation methods of CdTe thin films mainly include liquid phase epitaxy (LPE), near space sublimation, vapor transport deposition, sputtering, electrochemical deposition, and spray thermal decomposition.
The high efficiency of CdTe thin film solar batteries makes them occupy a certain share in the photovoltaic market, and CdTe thin film solar Batteries can achieve flexibility and transparency, which increases their application prospects in the automotive and construction industries. However, both Cd and Te are toxic elements, which limit the promotion and application of CdTe thin-film solar Batteries to a certain extent. Therefore, the focus of future research should be to reduce the content of toxic elements while improving the efficiency or to improve the stability of the battery itself and reduce the risk of leakage of toxic elements.
2. GaAs thin film solar Batteries
GaAs is a direct band gap (Eg=1.43eV) group III-V compound semiconductor material. The preparation methods of GaAs thin film solar Batteries have gone through diffusion method, LPE, metal-organic chemical vapor deposition (MOCVD), and so on.
GaAs thin film solar Batteries have many advantages, such as high conversion efficiency, good radiation resistance, and high-temperature resistance, and can be made into hetero-substrate solar Batteries and multi-junction solar Batteries, which increases the application prospect of GaAs solar Batteries in aerospace. However, the production cost of GaAs thin film batteries is too expensive and the toxic properties of As limit the application of such batteries in the civilian field. Therefore, the focus of future research should be to simplify the Battery fabrication process and to find abundant and non-toxic elements to replace the As element, so as to broaden the application space of this type of solar Battery.
3. Copper indium gallium selenide thin film solar Batteries
CIGS thin film solar Batteries are made of copper indium selenide thin film (CIS) thin film solar Batteries by replacing part of indium (In) with Ga element. The typical structure of CIGS thin film solar Batteries is TCO/ZnO/CdS/CIGS/back electrode/substrate. The main preparation methods of CIGS thin film solar Batteries are sputtering, MOCVD, liquid spraying, spraying pyrolysis, screen printing, and electrodeposition.
CIGS thin-film solar Batteries have the advantages of high efficiency, long lifetime, no photodegradation effect, and can be deposited on flexible polymer and metal substrates. However, CIGS thin-film solar Batteries also have some disadvantages, such as many synthetic materials, complex synthesis process, and rare elements In and toxic elements Cd in the synthetic materials, which not only make the battery cost too high but also cause serious environmental pollution. Aiming at the disadvantages of rare or toxic elements, inexpensive Zn and Sn are used to replace expensively In and Ga to obtain Cu2ZnSn(S, Se)4(CZTSSe) thin film solar Batteries similar to CIGS Batteries. CZTSSe thin film solar Batteries are not only environmentally friendly, but also CZTSSe is a direct bandgap material with a large absorption coefficient. Therefore, by reducing the thickness of the thin film battery, the number of materials used can be reduced, thereby reducing the overall cost of this type of battery.