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 CdS/Sb₂S₃ heterojunction quality, affected by the 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 and 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.