Interfacial Bridge Bonding Enables High‐Efficiency Sb₂(S,Se)₃ Solar Cells with Record Fill Factor Exceeding 73%

Abstract For solar cells, interfacial chemical coordination, carrier transport, and energy alignment play critical roles in carrier transport and determine the final energy conversion efficiency. As an emerging solar technology, high‐efficiency Sb₂(S,Se)₃ solar cells typically utilize cadmium sulfide (CdS) as the interfacial electron transport layer. However, the poor chemical and electrical contact between F‐doped SnO₂ (FTO) substrate and CdS presents a significant challenge to improving device performance. Here, an ultrathin SnO₂ layer is introduced, fabricated via chemical bath deposition, between FTO and CdS to address the interfacial coordination and transport problem. The non‐invasive depth analysis based on synchrotron radiation X‐ray photoelectron spectroscopy shows that this interfacial engineering approach facilitates the formation of S‐Sn bonding at the FTO/CdS interface, which cannot be achieved on the conventional inert FTO surface. Additionally, the existence of an interfacial SnO₂ layer reduces the sulfur vacancy defect (V_S) in the CdS films, enhancing both electrical conductivity and crystallinity. Therefore, the solar cell demonstrates significantly enhanced carrier separation and transport performance. Ultimately, the Sb₂(S,Se)₃ solar cells achieve a record fill factor exceeding 73%, with a championefficiency of 10.58%. This study presents an effective interfacial engineering strategy to enhance charge transport properties for high‐performance Sb₂(S,Se)₃ solar cells.