Synergistic Effect of Defects Passivation and Energy Level Alignment Realizing P3HT‐Based High‐Efficiency CsPbI3 Perovskite Solar Cells

Abstract Poly (3‐hexylthiophene) (P3HT) is one of the most efficient hole transport layers (HTLs) in perovskite solar cells (PSCs). However, surface and boundary defects in CsPbI 3 , and energy level mismatch between CsPbI 3 and P3HT lead to a low power conversion efficiency (PCE) in P3HT‐based CsPbI 3 PSCs. Here, a synergistic strategy with anti‐solvent (sec‐pentyl alcohol, 2‐PA) and passivators (LiX, X = F, Cl, Br, I) is developed to promote the photovoltaic performance of P3HT‐based CsPbI 3 PSCs. It is proved that the 2‐PA washes away the residual DMF and DMAPbI 3 , and assists the secondary growth of CsPbI 3 crystal. LiX not only can passivate iodine (I) vacancies, but also can reduce energy offset at CsPbI 3 /P3HT interface, accelerating hole extraction process. Finally, an impressive efficiency of 19.26% is obtained due to the synergistic effect of defects passivation and energy alignment, which is 34.4% higher than the 14.32% achieved in Control cell. These findings prove that synergistic strategy of defects passivation and energy alignment is an effective way for realizing high‐efficiency in P3HT‐based CsPbI 3 PSCs.