LiCl doping modulated PbS hole-transport layer for high-efficiency Sb2(S,Se)3 solar cells

The efficiency of Sb2(S,Se)3 solar cells is primarily limited by severe back-interface non-radiative recombination due to unfavorable band alignment and defects, thus making low-cost, stable, and suitably bandgap-matched PbS a promising inorganic HTL to address this issue. Nevertheless, its intrinsically low conductivity, coupled with the tunable surface electronic structure of Sb2(S,Se)3, results in a significant energy level mismatch and thus a high hole transport barrier at the Sb2(S,Se)3/PbS interface. This work presents a facile ion doping strategy (IDS) by doping of lithium ions (Li+) into the PbS lattice. The IDS increases the carrier concentration, enhances the p-type conductivity of PbS, optimizes its energy level position, and simultaneously passivates the interface defects, suppressing non-radiative recombination. The interface level alignment of Sb2(S,Se)3/PbS is optimized, significantly reducing the valence band offset barrier for hole transport from 0.21 to 0.14 eV, greatly promoting the extraction and transport of holes across the interface. Ultimately, the photoelectric conversion efficiency (PCE) of the FTO/CdS/Sb2(S,Se)3/Li-PbS/carbon device reaches 9.36% (Voc = 0.53 V, Jsc = 27.80 mA/cm2, FF = 63.86%), significantly outperforming the champion unmodified device (PCE = 7.41%). This work provides an efficient solution for HTL modification in chalcogenide solar cells.