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 TiCl _4 treatment on a compact TiO _2 layer used as an electron transport material (ETM) in Sb _2 S _3 planar solar cells. After TiCl _4 treatment, TiO _2 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 Sb _2 S _3 films grown on pristine or TiCl _4 treated TiO _2 films, there are differences in preferential growth of Sb _2 S _3 (hk1) planes, sulfur-enrichment of the chalcogenide film, and superior substrate coverage after the TiCl _4 treatment, leading to the decrease of interfacial trap states. The driving force for electron injection in the TiO _2 /Sb _2 S _3 heterojunction is also favored by the shift on the VB and CB positions of TiCl _4 treated TiO _2 . These findings are in agreement with the improved power conversion efficiency of the planar solar cell FTO/TiO _2-Treated /Sb _2 S _3 /SbCl _3 /spiro-OMeTAD/Au.