Asymmetric carbazole-based hole transport material for perovskite solar cells

Hole transport materials (HTMs) are essential for restricting charge recombination in perovskite solar cells (PSCs). Asymmetric HTMs, though rarely reported, have exhibited significantly improved molecular dipolar moment and interesting charge transport properties compared to their symmetrical counterparts. In this work, we report an asymmetric HTM, MC-ACD, based on a 9-(4-methoxyphenyl)-9H-carbazole core functionalized with two different donor groups. The designed conjugated planar asymmetric configuration promotes extensive π-electron delocalization and facilitates stronger intermolecular π-π stacking, thereby significantly enhancing charge transport efficiency. As a result, PSCs incorporating MC-ACD render a remarkable power conversion efficiency (PCE) of 24.2 %, surpassing both fluorene-based analogs (22.96 %) and the widely used Spiro-OMeTAD (22.52 %). This work provides critical insights for developing efficient, structurally simple small molecule HTMs for next-generation solar energy conversion systems.