Large‐Grained Antimony Selenosulfide Thin Films With V‐Shaped Bandgap Enable High‐Efficiency Planar Heterojunction Solar Cells

Sb 2 (S,Se) 3 is an emerging absorber with tunable bandgaps for next‐generation thin‐film photovoltaics. However, the performance of Sb 2 (S,Se) 3 solar cells is largely limited by severe charge‐carrier recombination and retarded charge transport due to high grain‐boundary (GB) density and unfavorable reverse‐gradient band structure in absorber films. This work demonstrates the large‐area‐compatible chemical bath deposition (CBD) of large‐grained Sb 2 (S,Se) 3 films with V‐shaped bandgap for enhanced performance through the incorporation of pre‐deposited Sb 2 S 3 seed layer coupled with two‐step annealing. Through extensive characterization of structural, morphological, energy band, defects and optoelectronic properties, complemented with device simulations, it is revealed that this modified CBD offers two benefits: (1) the deposition of absorber films with grain size exceeding 9 µm, the largest reported thus far for ternary Sb 2 (S,Se) 3 , which contributes to the reduction of defects at GBs for suppressed nonradiative recombination, and (2) the construction of favorable V‐shaped bandgap within Sb 2 (S,Se) 3 absorber, which promotes the efficient charge transport and extraction. The resulting planar heterojunction Sb 2 (S,Se) 3 solar cells achieve an impressive power conversion efficiency of 8.53%, which is among the top efficiencies for CBD‐processed antimony chalcogenide photovoltaics. This work provides valuable insights into the grain and band engineering in antimony chalcogenides for high efficiency thin‐film solar cells.