Hole‐Transport Materials Containing Triphenylamine Donors with a Spiro[fluorene‐9,9′‐xanthene] Core for Efficient and Stable Large Area Perovskite Solar Cells

Three low‐cost triphenylamine‐based hole‐transport materials (HTMs) with spiro[fluorene‐9,9‐xanthene] (SFX) skeleton are synthesized through a facile three‐step procedure. The effect of the chemical structure of the HTMs on the optical property, energy levels, H 2 O/HTM interface, as well as the perovskite solar cell performance are studied. With the increasing bulkiness of attached groups on the SFX skeleton, the charge recombination resistance at the TiO 2 /perovskite/HTMs interfaces is gradually increased, leading to increased open‐circuit voltages. The device based on the bulkiest HTM (named BTPA‐6) exhibits a better solar cell performance (11.57%, area: 1.02 cm 2 ) than those with BTPA‐4 and BTPA‐5 in the forward scan. BTPA‐6 also exhibits a power conversion efficiency of 14.4% (area: 0.375 cm 2 ) which nearly matches spiro‐OMeTAD (15.0%) in the reverse scan. Furthermore, all the three cost‐effective (∼1/3 of that of spiro‐OMeTAD) HTMs exhibit better long‐term stabilities than spiro‐OMeTAD.