Understanding the effect of TiCl4 treatment at TiO2/Sb2S3 interface on the enhanced performance of Sb2S3 solar cells

The continuous search for low-cost and environment-friendly materials in photovoltaic applications has become a priority, as well as the understanding of the various strategies to boost the photovoltaic performance. In this work, we investigate the effect of TiCl4 treatment on a compact TiO2 layer used as an electron transport material (ETM) in Sb2S3 planar solar cells. After TiCl4 treatment, TiO2 exhibits higher crystallinity, lower density of hydroxyl groups acting as traps, and better surface coverage of the FTO substrate. Although no major structural changes are observed in Sb2S3 films grown on pristine or TiCl4 treated TiO2 films, there are differences in preferential growth of Sb2S3 (hk1) planes, sulfur-enrichment of the chalcogenide film, and superior substrate coverage after the TiCl4 treatment, leading to the decrease of interfacial trap states. The driving force for electron injection in the TiO2/Sb2S3 heterojunction is also favored by the shift on the VB and CB positions of TiCl4 treated TiO2. These findings are in agreement with the improved power conversion efficiency of the planar solar cell FTO/TiO2-Treated/Sb2S3/SbCl3/spiro-OMeTAD/Au.