Effects of junction formation conditions on the photovoltaic properties of sintered CdS/CdTe solar cells

Microstructures and properties of sintered CdS films on glass substrates and sintered CdTe films on polycrystal CdS substrates have been investigated. The CdS films, which contained 9 wt % CdCl₂ as a sintering aid and were sintered at 650° C for 1 h in nitrogen, are transparent and have an average grain size of 15m and an electrical resistivity of 0.5cm. The CdTe films, which were coated on the sintered CdS substrate and were sintered above 610° C for 1 h in nitrogen, have a dense structure with an average grain size larger than 5m. All polycrystal CdS/CdTe solar cells were fabricated by this successive coating and sintering method. The sintering temperature of CdTe films on the sintered CdS films was varied from 585 to 700° C. Compositional interfaces and p-n juctions are formed during sintering. The highest solar efficiency (7.18%) was found in a solar cell made by sintering the composite layer of glass-CdS-CdTe at 625° C for 1 h. A fabrication temperature below 610° C resulted in poor solar cell efficiencies due to the porous structure of the CdTe films and above 650° C also resulted in poor efficiencies due to the formation of a CdS_1-x Te_x layer at the interface and a large p-n junction depth.