Orbital Interactions in 2D Dion–Jacobson Perovskites Using Oligothiophene-Based Semiconductor Spacers Enable Efficient Solar Cells

2D Dion–Jacobson (DJ) perovskites have emerged as promising photovoltaic materials, but the insulating organic spacer has hindered the efficient charge transport. Herein, we successfully synthesized a terthiophene-based semiconductor spacer, namely, 3ThDMA, for 2D DJ perovskite. An interesting finding is that the energy levels of 3ThDMA extensively overlap with the inorganic components and directly contribute to the band formation of (3ThDMA)PbI4, leading to enhanced charge transport across the organic spacer layers, whereas no such orbital interactions were found in (UDA)PbI4, a DJ perovskite based on 1,11-undecanediaminum (UDA). The devices based on (3ThDMA)MAn–1PbnI3n+1 (nominal n = 5) obtained a champion efficiency of 15.25%, which is a record efficiency for 2D DJ perovskite solar cells using long-conjugated spacers (conjugated rings ≥ 3) and a 22.60% efficiency for 3ThDMA-treated 3D PSCs. Our findings provide an important insight into understanding the orbital interactions in 2D DJ perovskite using an organic semiconductor spacer for efficient solar cells.