Halogen Radical‐Activated Perovskite‐Substrate Buried Heterointerface for Achieving Hole Transport Layer‐Free Tin‐Based Solar Cells with Efficiencies Surpassing 14 %

Abstract Sn‐based perovskites have emerged as one of the most promising environmentally‐friendly photovoltaic materials owing to their low toxicity and exceptional optoelectronic properties. Nonetheless, the low‐cost production and stable operation of Sn‐based perovskite solar cells (PSCs) are still largely limited by the costly hole transport materials and the under‐optimized interfaces between hole transport layer (HTL) and Sn perovskite layer. Here, we innovatively developed a chlorine radical chemical bridging (Cl‐RCB) strategy that enabled to remove the HTL and optimize the indium tin oxide (ITO)/perovskite heterointerface for constructing high‐performance Sn‐based PSCs with simplified structures. The key is to modify the commercially‐purchased ITO electrode with highly active chlorine radicals that could effectively mitigate the surface oxygen vacancies, alter the chemical constitutions, and favorably down‐shifted the work function of ITO surface to be close to the valence band of perovskites. As a result, the interfacial energy barrier has been largely reduced by 0.20 eV and the interfacial carrier dynamics have been optimized at the ITO/perovskite heterointerface. Encouragingly, the efficiency of HTL‐free Sn‐based PSCs has been enhanced from 6.79 % to 14.20 %, which is on par with the state‐of‐the‐art conventional HTL‐containing counterparts (normally >14 % efficiency) and representing the record performance for the Sn perovskite photovoltaics in the absence of HTL. Notably, the target device exhibited enhanced stability for up to 2000 h. The Cl‐RCB strategy is also versatile to be used in Pb‐based and mixed Sn−Pb HTL‐free PSCs, achieving efficiencies of 22.27 % and 21.13 %, respectively, all representing the advanced device performances for the carrier transport layer‐free PSCs with simplified device architectures.