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 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.