Solution-Processed Sb 2 S 3 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 SbCl 3 Interface Layer.

Interfaces in Sb ₂ S ₃ thin-film solar cells strongly affect their open-circuit voltage ( V _OC ) and power conversion efficiency (PCE). Finding an effective method of reducing the defects is a promising approach for increasing the V _OC and PCE. Herein, the use of an inorganic salt SbCl ₃ is reported for post-treatment on Sb ₂ S ₃ films for surface passivation. It is found that a thin SbCl ₃ layer could form on the Sb ₂ S ₃ 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 Sb ₂ S ₃ surface by SbCl ₃ occurs via the interactions of Sb and Cl in SbCl ₃ molecules with S and Sb in Sb ₂ S ₃ , respectively. As a result, incorporating the SbCl ₃ layer highly improves the V _OC 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 cm ² . The achieved PCE is the highest value in the Sb ₂ S ₃ planar solar cells. In addition, the incorporated SbCl ₃ layer also leads to good stability of Sb ₂ S ₃ 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.