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 (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 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 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 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.