Abstract

The efficient functioning of perovskite solar cells largely depends on the interaction between perovskite halide materials and the hole‐transport layer poly(3‐hexylthiophene) (P3HT). However, a high rate of nonradiative recombination often hampers this interaction, leading to poor performance of the solar cells. We have developed a technique to modify the interface using a long‐chain alkyl halide molecule called n ‐hexyl trimethylammonium bromide to address this issue. This modification technique significantly improves hole extraction, leading to an impressive open‐circuit voltage of 1.14 V and a power conversion efficiency of 15.8% for inorganic perovskite CsPbI 3 with P3HT as a dopant‐free hole‐transport layer. This breakthrough can pave the way for developing more efficient and sustainable solar cells.