Enhanced efficiency of Sb2S3 solar cells via heterojunction interfacial MgCl2-CdCl2 mixed treatment

Antimony sulfide (Sb2S3) solar cells exhibit significant potential in tandem and indoor photovoltaic applications. The quality of cadmium sulfide (CdS)/Sb2S3 heterojunction, affected by energy-level misalignments and lattice-mismatch defects, is crucial for achieving high-performance devices. Herein, we propose a MgCl2-CdCl2 mixed treatment strategy for the CdS/Sb2S3 interface to suppress interfacial recombination caused by defects and energy band offsets. The obtained preferentially [100]-oriented CdS film effectively mitigates lattice mismatch and induces the subsequent hydrothermal deposition of a well-crystallized, vertically oriented Sb2S3 absorber. The MgCl2-CdCl2 mixed treatment introduces Mg2+ doping in the CdS layer, achieving an enhanced surface potential and well-matched interfacial energy band alignments. The CdS/Sb2S3 heterojunction interface forms a spike-type energy band structure with a small conduction band offset. Compared with the conventional CdCl2 treatment, the MgCl2-CdCl2 mixed-treated device exhibits a stronger built-in electric field (1.31 V) and low-temperature activation energy (1.63 eV), indicating the suppression of carrier recombination. Consequently, the champion Sb2S3 solar cells achieve an improved efficiency from 7.5% to 8.1%. This heterojunction treatment strategy is expected to provide an effective method for fabricating high-performance inorganic thin film solar cells.