Solution-Processed Sb₂S₃ Planar Thin Film Solar Cells with a Conversion Efficiency of 6.9% at an Open Circuit Voltage of 0.7 V Achieved via Surface Passivation by a SbCl₃ Interface Layer

Interfaces in Sb2S3 thin-film solar cells strongly affect their open-circuit voltage (VOC) and power conversion efficiency (PCE). Finding an effective method of reducing the defects is a promising approach for increasing the VOC and PCE. Herein, the use of an inorganic salt SbCl3 is reported for post-treatment on Sb2S3 films for surface passivation. It is found that a thin SbCl3 layer could form on the Sb2S3 surface and produce higher efficiency cells by reducing the defects and suppressing nonradiative recombination. Through density functional theory calculations, it is found that the passivation of the Sb2S3 surface by SbCl3 occurs via the interactions of Sb and Cl in SbCl3 molecules with S and Sb in Sb2S3, respectively. As a result, incorporating the SbCl3 layer highly improves the VOC from 0.58 to 0.72 V; an average PCE of 6.9 ± 0.1% and a highest PCE of 7.1% are obtained with an area of 0.1 cm2. The achieved PCE is the highest value in the Sb2S3 planar solar cells. In addition, the incorporated SbCl3 layer also leads to good stability of Sb2S3 devices, by which 90% of the initial performance is maintained for 1080 h of storage under ambient humidity (85 ± 5% relative humidity) at room temperature.