Fluorinated Fullerene Derivatives for Tin Halide Perovskite Solar Cells With Reduced Carrier Transport Losses

Tin halide perovskite solar cells (Sn‐PSCs) are promising alternatives to their lead‐based counterparts. However, their performance remains limited by high non‐radiative recombination at interfaces, which compromises charge extraction and ultimately leads to poor charge transport and fill factor (FF) losses. Herein, we present the synthesis and application of two novel fluorinated C ₇₀ ‐based fulleropyrrolidines as precursor additives in Sn‐PSCs. Due to their dual functionality, the fluorinated moieties effectively passivate structural defects, reducing trap states and reducing non‐radiative recombination. On its part, the C ₇₀ cage provides high electron affinity, which facilitates charge transport across perovskite and improves charge extraction at the perovskite/ETL interface. These effects lead to a significant enhancement in the average FF, from 64 to 72%, directly increasing the PCE of champion devices from 11.7% for reference devices up to 12.7% for devices with C ₇₀ additives. Moreover, C ₇₀ ‐modified devices also exhibited a prolonged shelf stability, retaining up to 97% of their initial efficiency after more than 350 h of storage. Overall, this work demonstrates that C ₇₀ derivatives can be employed as effective additives in Sn‐PSCs to mitigate charge transport losses and boost FF, providing a reliable strategy to enhance performance in Pb‐free optoelectronics.