The application of a statistical methodology to investigate deposition parameters in CdTe/CdS solar cells grown by MOCVD

Abstract

A L8 matrix of experiments has been carried out to investigate various deposition parameters of Cadmium telluride (CdTe)/Cadmium sulphide (CdS) solar cells grown using metal organic chemical vapour deposition (MOCVD). The results of the matrix were analysed using a criterion to establish which growth parameters are significant and warrant further investigation. The most significant parameters were CdTe growth temperature and in situ arsenic doping of the CdTe absorber layer. Characterisation of the device structures showed that CdTe grain enlargement from 1 μm to ∼3 μm occurred at the higher CdTe deposition temperature of 390 °C. SIMS depth profiles verified that arsenic concentrations, within the device structures, of 2.5 × 1018 and 2 × 1019 atoms cm−3 were achieved for the different partial pressures. A model for the behaviour of arsenic in polycrystalline CdTe material, based on only partial passivation of grain boundaries and saturation of the grain boundaries at As concentrations above >2.5 × 1018 atoms cm−3 is presented and discussed.