Celdas solares de heterounión de CdS/CdTe. Parte I. Celdas solares procesadas por la técnica GREG

In this paper we present the processing and characterization of thin film CdS/CdTe solar cells obtained by the gradient recrystallization and growth technique, GREG. The cells were deposited on soda-lime LOF™ conducting glass substrates and Cu-Au contacts were evaporated on top of the CdTe film. The films deposition conditions were: for CdS the source temperature T_f varied between 750°C and 800°C and the substrate temperature T_s varied between 480°C and 550°C, while for CdTe T_f varied between 570°C and 650° C and T_s from 460°C to 480°C; both films were deposited under a constant Ar gas pressure. The films were characterized by X-ray diffraction, atomic force microscopy, optical absorption and photoluminiscence. Both CdS and CdTe films were polycrystalline with preferential orientation in the [002] direction for CdS and in the [111] direction for CdTe; the grain size ranges for the films were 0.2-1 μm for CdS and 0.5-5 μm for CdTe. The solar cell photoconductive parameters were determined yielding the best cell performance values of V_OC = 0.7 V, J_SC = 31 mA/cm², f f = 50%, SQE_max = 0.6 electr./photon at 550 nm and 8% solar energy conversion efficiency.