CHARACTERIZATION OF THIN-FILM ZNO ZNCDS/CUGASE2 HETEROJUNCTIONS/

Polycrystalline thin film solar cells with structure ZnO/ZnCdS/CuGaSe2 were fabricated. The absorber layers of CuGaSe2 were prepared by lase r assisted evaporation. A multilayer window consisting of reactively e vaporated ZnO and sprayed ZnCdS was deposited onto CuGaSe2 to complete the cell; ZnO improves the light coupling and window sheet resistance , and ZnCdS serves as a buffer layer. The electrical and optical prope rties of the individual layers were studied. The junction behaviour wa s evaluated using current density-voltage, capacitance-voltage and qua ntum efficiency measurements, showing that the junction transport is c ontrolled by tunnelling at low temperatures and recombination above ro om temperature. A conversion efficiency of 5.8% was obtained on an are a of 1 cm(2) with cell parameters V-oc = 700 mV, J(sc) = 12.5 mA cm(-2 ) and FF = 0.56 without antireflection coating. The results obtained a re presented and the requirements for optimizing the device efficiency are discussed.