Synergistic effects of bithiophene ammonium salt for high-performance perovskite solar cells

Abstract

Simultaneously improving the charge transfer and suppressing the charge recombination at the interface is essentially important for high-performance perovskite solar cells (PVSCs). To achieve this goal, in this work, we modify the anode interface of PVSCs with a ligand, bithiophenethylammonium iodide (2TEAI), which comprises both long-conjugation bithiophene and ammonium groups. With 2TEAI, high-performance FAPbI₃ (FA: HC(NH₂)₂) based PVSCs with significantly increased efficiency from 21.7% to 23.6% have been demonstrated for small area devices, as well as 21.3% for large-area (2.25 cm²) devices. Comprehensive analysis of the carrier dynamics and first-principles simulations unveils that the 2TEAI modification can (1) enhance the interfacial charge transfer due to energy level alignment between the highest occupied molecular orbital and the perovskite valence band, and (2) mitigate the charge recombination by passivating the trap states owing to its strong chemical interaction perovskite layer and reduction of Pb⁰. Our work demonstrates a reliable strategy to optimize the interface and paves the way toward high-performance PVSCs for commercialization.