Unprecedented inorganic HTL-based MA-free Sn–Pb perovskite photovoltaics with an efficiency over 23%

Abstract

The majority of high-efficiency Sn–Pb perovskite solar cells (PSCs) have used methylammonium (MA) cation and PEDOT:PSS hole transport layer (HTL) which limits the device performance, especially in terms of stability. In this work, we propose a highly efficient and remarkably stable MA-free Sn–Pb PSC based on an inorganic HTL (NiO_x), utilizing GeO_x passivation derived from GeI₂ additive. Using depth profiling analysis, we demonstrate for the first time that GeI₂ additive–GeO_x has a very detrimental effect on the PEDOT:PSS/Sn–Pb perovskite system, while it is efficacious on the NiO_x/Sn–Pb perovskite system. The GeI₂ additive–GeO_x passivation effectively mitigates defect states and non-radiative recombination in the MA-free Sn–Pb perovskite by inhibiting Ni³⁺ formation and efficiently suppressing Sn²⁺ oxidation in the NiO_x/Sn–Pb perovskite system. Additionally, the GeO_x on the NiO_x surface exhibits excellent band alignment, resulting in outstanding charge extraction. Consequently, our MA-free Sn–Pb PSC shows an unprecedented efficiency of 23.34% (certified 22.9%) which is the highest among MA-free Sn–Pb PSCs employing an inorganic HTL instead of PEDOT:PSS, and exhibits exceptional long-term stability, maintaining over 95% of the initial power conversion efficiency for 4320 hours with encapsulation (88% without encapsulation). Our findings suggest promising prospects for efficient and stable MA-free Sn–Pb photovoltaic devices, potentially replacing PEDOT:PSS.