Synergistic Effect of Defects Passivation and Energy Level Alignment Realizing P3HT‐Based High‐Efficiency CsPbI ₃ 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.