Analysis of Se Co-evaporation and Post-selenization for Sb2Se3-Based Solar Cells

Sb2Se3 is a promising alternative absorber material for thin-film solar cells. However, by a thermal evaporation technique, it appears to partially decompose, leading to Se deficiency. In this work, we propose two alternative routes for the supply of selenium in the deposition of Sb2Se3 thin films. The first method is the co-evaporation of Se and Sb2Se3, while the second is the post-deposition selenization. Superstrate glass/FTO/TO/CdS/Sb2Se3/Au-configured thin-film cells are grown using thermal evaporation. X-ray diffraction patterns confirm the presence of CdS peaks along with the preferred (hk1) oriented grains, which are suppressed upon selenization. Modified surface morphology for the selenized samples is observed by atomic force microscopy. Enhanced current density is observed by J-V characterization and also confirmed by a remarkable external quantum efficiency (EQE) gain at long wavelengths. However, CdS deterioration reduces the EQE response in the short wavelength region, acting as a limiting factor for the efficiency improvement. The champion cell shows a power conversion efficiency of 3.6% with an open circuit voltage of 352 mV and a fill factor of 44.2%, which results in, to our knowledge, the highest value for thermally evaporated Sb2Se3 in superstrate configuration.