Molten Salts Assisted Interfacial Engineering for Efficient and Low‐Cost Full‐Inorganic Antimony Sulfide Solar Cells

Abstract Antimony sulfide (Sb₂S₃) is emerging as a promising light harvesting material owing to its brilliant photoelectric property. However, the performance of Sb₂S₃‐based solar cells is partly limited by serious back contact interface recombination and hole transportation resistance. High‐efficiency Sb₂S₃ devices typically use Spiro‐OMeTAD and/or Au as back contact materials, but their stability and cost are a concern. In this sense, a surface modification scheme by lithium‐doping is first introduced for Sb₂S₃ via a facile molten salt method. The ions in the molten state have high mobility and activity, enabling doping reactions to complete within a short time. The lithium‐doped Sb₂S₃ thin film has a smooth and well‐bonded surface, preferred (hk1) orientations, and an upshifted valence band maximum (VBM), which favors the hole extraction. Finally, a device using carbon as an electrode, which is more than a dozen times cheaper than gold, raises the short‐circuit current density (J_SC) from 12.35 to 14.40 mA cm⁻², and the power conversion efficiency (PCE) from 4.47% to 6.16%. This is among the highest PCE reported for full‐inorganic Sb₂S₃ solar cells, which demonstrates a facile interface modification technique via molten alkali salt to improve the performance of Sb₂S₃ solar cells.