Triphenylamine-Based Hole-Transporting Ligands for 2D/3D FAPbI3 Perovskite Solar Cells

Two-dimensional (2D) perovskites suffer from poor charge transport due to the insulating nature of typically used organic spacers. Here, we develop a triphenylamine (TPA)-functionalized semiconducting ligand, namely, DPA-PEAI, in which the TPA moiety is tethered to the ethylammonium cation. Crystallographic analysis of n = 1 2D perovskite (DPA-PEA)2PbI4 reveals that the propeller-like geometry and enriched phenyl rings of the TPA tail enable the formation of multifarious π-stacking interconnections between neighboring ligands. Theoretical calculations further unveil that both the binding energy and hole transfer integral are augmented between the adjacent DPA-PEA cations, in contrast to the widely used phenylethylammonium (PEA) counterpart. This cross-electronic coupling feature allows the formation of multiple hole-transfer pathways within DPA-PEA-based 2D perovskites, enabling efficient out-of-plane charge transport, as confirmed by a set of characterizations. As a consequence, 2D/3D FAPbI3-based PSCs employing DPA-PEAI afford a champion efficiency of 25.7%, which ranks among the best efficiencies reported for conjugative ligands.