Grain Engineering of Sb₂S₃ Thin Films to Enable Efficient Planar Solar Cells with High Open‐Circuit Voltage

Abstract Sb₂S₃ is a promising environmentally friendly semiconductor for high performance solar cells. But, like many other polycrystalline materials, Sb₂S₃ is limited by nonradiative recombination and carrier scattering by grain boundaries (GBs). This work shows how the GB density in Sb₂S₃ films can be significantly reduced from 1068 ± 40 to 327 ± 23 nm µm⁻² by incorporating an appropriate amount of Ce³⁺ into the precursor solution for Sb₂S₃ deposition. Through extensive characterization of structural, morphological, and optoelectronic properties, complemented with computations, it is revealed that a critical factor is the formation of an ultrathin Ce₂S₃ layer at the CdS/Sb₂S₃ interface, which can reduce the interfacial energy and increase the adhesion work between Sb₂S₃ and the substrate to encourage heterogeneous nucleation of Sb₂S₃, as well as promote lateral grain growth. Through reductions in nonradiative recombination at GBs and/or the CdS/Sb₂S₃ heterointerface, as well as improved charge‐carrier transport properties at the heterojunction, this work achieves high performance Sb₂S₃ solar cells with a power conversion efficiency reaching 7.66%. An impressive open‐circuit voltage (V_OC) of 796 mV is achieved, which is the highest reported thus far for Sb₂S₃ solar cells. This work provides a strategy to simultaneously regulate the nucleation and growth of Sb₂S₃ absorber films for enhanced device performance.