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

Sn-based perovskites have emerged as one of the most promising environmentally-friendly photovoltaic materials. Nonetheless, the low-cost production and stable operation of Sn-based perovskite solar cells (PSCs) are still limited by the costly hole transport layer (HTL) and the under-optimized interfacial carrier dynamics. Here, we innovatively developed a halogen radical chemical bridging strategy that enabled to remove the HTL and optimize the perovskite-substrate heterointerface for constructing high-performance, simplified Sn-based PSCs. The modification of ITO electrode by highly active chlorine radicals 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 was reduced by 0.20 eV and the carrier dynamics were optimized at the ITO/perovskite heterointerface. Encouragingly, the efficiency of HTL-free Sn-based PSCs was enhanced from 6.79% to 14.20%, representing the record performance for the Sn perovskite photovoltaics in the absence of HTL. Notably, the target device exhibited enhanced stability for 2000 h. The Cl-RCB strategy is also versatile to construct 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.