Dopant‐Free Donor (D)–π–D–π–D Conjugated Hole‐Transport Materials for Efficient and Stable Perovskite Solar Cells

Three novel hole‐transporting materials (HTMs) using the 4‐methoxytriphenylamine (MeOTPA) core were designed and synthesized. The energy levels of the HTMs were tuned to match the perovskite energy levels by introducing symmetrical electron‐donating groups linked with olefinic bonds as the π bridge. The methylammonium lead triiodide (MAPbI 3 ) perovskite solar cells based on the new HTM Z34 (see main text for structure) exhibited a remarkable overall power conversion efficiency (PCE) of 16.1 % without any dopants or additives, which is comparable to 16.7 % obtained by a p‐doped 2,2′,7,7′‐tetrakis‐( N , N ‐di‐4‐methoxyphenylamino)‐9,9′‐spirobifluorene (spiro‐OMeTAD)‐based device fabricated under the same conditions. Importantly, the devices based on the three new HTMs show relatively improved stability compared to devices based on spiro‐OMeTAD when aged under ambient air containing 30 % relative humidity in the dark.