Anion‐Vacancy Defect Passivation for Efficient Antimony Selenosulfide Solar Cells via Magnesium Chloride Post‐growth Activation

The quasi-1D antimony selenosulfide (Sb2(S,Se)3) light-harvesting material has attracted tremendous attention for photovoltaic applications because of its superior materials and optoelectronic properties. However, one of the critical obstacles faced by Sb2(S,Se)3 solar cells is the presence of many defects in absorbers, especially those deep-level anion-vacancy defects which are prone to serving as recombination centers. In this work, an effective defect engineering strategy via magnesium chloride (MgCl2) postgrowth activation is explored for high performance antimony selenosulfide solar cells. Through careful characterization of structural, morphological, and defect properties, as well as the photovoltaic performance, complemented with firs-principle calculations, it is revealed that this postgrowth activation step enables the effective passivation of deep-level anion-vacancy defects via electrical chloride-doping, the recrystallization of small grains for producing large-grained films, and the formation of favorable cascade energy levels to promote the charge transport. Benefitting from suppressed charge recombination and facilitated charge transport, the Sb2(S,Se)3 solar cells yield a considerable power conversion efficiency of 10.55%, which is among the top efficiencies reported for antimony chalcogenide solar cells. This study underscores the significance of anion-vacancy passivation for efficient antimony chalcogenide devices.