Molecular engineering of enamine‐based hole‐transporting materials for high‐performing perovskite solar cells: influence of the central heteroatom

Stabilizing the high-performing perovskite solar cells (PSCs) with low-cost and simply affordable hole-transporting materials (HTMs) has been identified as an ongoing ambitious challenge. Herein, a series of enamine-based HTMs having different central heteroatoms (C, N, O, and S) and a number of enamine branches is designed and synthesized. The impact of varied central heteroatom cores is investigated in-depth including thermal, photophysical, and photovoltaic properties. Importantly, molecularly engineered HTMs are obtained by a single condensation reaction without the need for expensive catalysts, inert reaction conditions, or tedious product purification. PSCs with a power conversion efficiency (PCE) of over 20% can be realized with the triphenylamine core HTM (V1435), a result comparable with spiro-OMeTAD. HTMs based on tetraphenylmethane (V1431) and diphenyl sulfide (V1434) cores give a slightly lower performance under similar device fabrication conditions. This work demonstrates how rational molecular engineering of a simple condensation approach can produce HTMs for high-performing PSCs without sacrificing the PCE.