Self‐Assembled Charge Bridge Path at the Sn‐Pb Perovskite/C60 Interface for High‐Efficiency All‐Perovskite Tandem Solar Cells

Abstract

Narrow bandgap mixed tin‐lead perovskite solar cells (PSCs) have garnered substantial research interest owing to their remarkable optoelectronic properties. However, non‐radiative recombination and carrier transport losses at the interface between the perovskite layer and the charge transport layer (C60) significantly reduce the overall efficiency of mixed tin‐lead PSCs. To address this challenge, 9‐Fluorenylmethyl carbazate (9FC) is incorporated at the interface between perovskite and C60. The hydrazide group present in 9FC effectively mitigates the oxidation of Sn2+. Furthermore, 9FC can engage in chemical bonding with the perovskite, while the outward‐facing aromatic rings create effective π–π interactions with C60, thereby promoting enhanced interfacial charge transfer. The highest‐performing mixed tin‐lead PSCs achieve a power conversion efficiency (PCE) of 23.97%, accompanied by an impressive open‐circuit voltage of 0.91 V. Additionally, these tin‐lead PSCs facilitate the development of highly efficient two‐terminal and four‐terminal all‐perovskite tandem solar cells, which demonstrate efficiencies of 27.01% and 28.07%, respectively.