Chlorination‐Enabled Oxygen Control and Dual‐Sulfur Source Aided Trap Passivation to Unlock 8.24% Efficient Sb ₂ S ₃ Photovoltaic Devices

Here, we present the fabrication of a high‐quality Sb 2 S 3 absorber layer enabled by a thioacetamide (TA) based dual sulfur source combined with electron transport layer (ETL) chlorination. The chlorination, viz. CdCl 2 heat treatment (CHT) is applied to CdS deposited over an industrially relevant inline‐processed SnO 2 /FTO substrate. A systematic investigation of TA and CHT effects, focusing on oxygen, sulfur, and chlorine chemistry, shows that incorporating TA as an additional sulfur source significantly enhances the absorber microstructure by promoting larger grains, suppressing hk0 orientations, and improving grain growth along hk1 orientation while reducing trap density in the Sb 2 S 3 films. Simultaneously, ETL CHT enhances the structural, interface, and optoelectronic properties of CdS, improving the Sb 2 S 3 absorber quality as measured by average grain size and the preferred hk1 orientation. Most importantly, ETL CHT processing substantially reduces the absorber's oxygen content, thereby lowering the overall oxygen/sulfur ratio and suppressing deleterious SbO x formation. The TA and ETL CHT combine to enable a PCE of 8.24% with a V OC ‐deficit <950 mV. These findings demonstrate a promising, low‐temperature synthesis route to reduce oxygen content, helping to overcome a long‐standing barrier in achieving higher PCE.