Back‐Contact Engineering via a MoO 3 /Ag Structure for Efficient Sb 2 (S,Se) 3 Thin‐Film Solar Cells

The quality of the back contact critically determines the hole extraction efficiency and interfacial recombination losses in Sb 2 (S,Se) 3 thin‐film solar cells. High‐efficiency devices typically use the Spiro‐OMeTAD/Au structure, but the reliance on Au electrodes increases material cost, creating an efficiency‐cost trade‐off. Here, we develop a cost‐effective Spiro‐OMeTAD/MoO 3 /Ag composite back contact that enables the use of a low‐cost electrode while maintaining efficient carrier extraction. The Spiro‐OMeTAD/MoO 3 /Ag composite back contact establishes a more favorable rear‐contact configuration, facilitating hole transfer while reducing carrier accumulation and interfacial recombination. Mild annealing further improves the back‐contact properties. Transient absorption spectroscopy (TAS), electrical, and photovoltaic measurements are interpreted together and consistently support improved interfacial carrier transfer with suppressed detrimental recombination. The optimized device achieves a PCE of 10.0%, approaching the performance level of reported Au‐based Sb 2 (S,Se) 3 cells while using a low‐cost Ag‐based electrode. This work demonstrates an effective, economical back‐contact engineering strategy that delivers high performance with cost‐effectiveness.