Replacement of Biphenyl by Bipyridine Enabling Powerful Hole Transport Materials for Efficient Perovskite Solar Cells

Here, 2,2′‐ and 3,3′‐bipyridine are introduced for the first time as the core structure to get two new hole transport materials (HTMs), namely F22 and F33. The electron‐withdrawing nature of bipyridine lowers the HOMO level of the new compounds and enhances the open‐circuit voltage of perovskite solar cells. Especially for F33, the better planarity leads to better conjugation in the whole molecule and the molecular interaction is enhanced. Hole‐mobility tests, steady‐state photoluminescence (PL) spectra as well as time‐resolved PL decay results demonstrate that the new HTMs exhibit good hole extraction and hole‐transporting property. Impressive power conversion efficiencies of 17.71 and 18.48 % are achieved in conventional planar perovskite (CH3NH3PbI3−xClx) solar cells containing F22 and F33 as HTMs, respectively. As far as we know, this is the first report on bypiridine‐based HTMs with leading efficiencies, and the design motif in this work opens a new way for devising HTMs in the future. Bip, bip: Bipyridine is introduced for the first time as the core structure for new hole transport materials (HTMs). Remarkable power conversion efficiencies of 17.71 and 18.48 % are achieved in conventional planar perovskite (CH3NH3PbI3−xClx) solar cells by using the newly devised HTMs.