Controllable Solution-Phase Epitaxial Growth of Q1D Sb₂(S,Se)₃/CdS Heterojunction Solar Cell with 9.2% Efficiency

Antimony sulfoselenide (Sb₂(S,Se)₃) is a promising photoabsorber for stable and high efficiency thin film photovoltaics (PV). The unique quasi-1D (Q1D) crystal structure gives Sb₂(S,Se)₃ intriguing anisotropic optoelectronic properties, which intrinsically require the optimization of crystal growth orientation, especially for electronic devices with vertical charge transport such as solar cells. Although the efficiency of Sb₂(S,Se)₃ solar cells has been improved greatly through optimizing the material quality, the fundamental issue of crystal orientation control in polycrystalline films remains unsolved, resulting in charge carrier recombination losses in the device. Herein, the epitaxial growth of vertically-oriented Sb₂(S,Se)₃ film on hexagonal CdS is successfully realized via a solution-based synergistic crystal growth process. The crystallographic orientation relationship between Sb₂(S,Se)₃ light absorber and the CdS substrate has been rigorously investigated. The best performing Sb₂(S,Se)₃ solar cell shows a high power conversion efficiency of 9.2% owing to the faster charge transport in the bulk and the efficient charge extraction across the heterojunction. This study points to a new direction to control the crystal growth of mixed-anion Sb₂(S,Se)₃, which is crucial to achieve high efficiency solar cells based on antimony chalcogenides with low dimensionality.