Grain Engineering of Sb₂ S₃ Thin Films to Enable Efficient Planar Solar Cells with High Open-Circuit Voltage

Sb₂ S₃ is a promising environmentally friendly semiconductor for high performance solar cells. But, like many other polycrystalline materials, Sb₂ S₃ is limited by nonradiative recombination and carrier scattering by grain boundaries (GBs). This work shows how the GB density in Sb₂ S₃ 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 Sb₂ S₃ 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 Ce₂ S₃ layer at the CdS/Sb₂ S₃ interface, which can reduce the interfacial energy and increase the adhesion work between Sb₂ S₃ and the substrate to encourage heterogeneous nucleation of Sb₂ S₃ , as well as promote lateral grain growth. Through reductions in nonradiative recombination at GBs and/or the CdS/Sb₂ S₃ heterointerface, as well as improved charge-carrier transport properties at the heterojunction, this work achieves high performance Sb₂ S₃ 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 Sb₂ S₃ solar cells. This work provides a strategy to simultaneously regulate the nucleation and growth of Sb₂ S₃ absorber films for enhanced device performance.