An Extraordinary Antisolvent Ethyl Cyanoformate for Achieving High Efficiency and Stability P3HT‐Based CsPbI3 Perovskite Solar Cells

Abstract Surface defects are always a severe problem in inorganic perovskite, superadding the mismatch of energy level between Poly(3‐hexylthiophene) (P3HT) hole transport layer (HTL) and CsPbI 3 perovskite. All these issues result in large losses in open‐circuit voltage ( V oc ) and fill factor ( FF ), and thus, CsPbI 3 perovskites solar cells (PSCs) based on P3HT HTL commonly show a lower power conversion efficiency (PCE). Herein, an extraordinary antisolvent engineering is proposed by ethyl cyanoformate (EC), that regulates the crystallization progress to improve the quality of CsPbI 3 perovskite film. Concomitantly, residual EC passivates the uncoordinated Pb 2+ defects by synergistical chemical interaction of C≡N and C═O groups, and energy level arrangement at the CsPbI 3 /P3HT interface is also optimized. As a result, the PCE of P3HT‐based CsPbI 3 PSC is improved to 18.46% from 17.33% of the control device. The unencapsulated CsPbI 3 PSCs show enhanced moisture stability and fine operational stability. The work reveals that EC is an extraordinary antisolvent, exhibiting a synergistic strategy in many aspects for obtaining high‐performance P3HT‐based CsPbI 3 PSCs. Furthermore, P3HT is doped with a small amount of 4‐Cyano‐4′‐pentylbipheny (5CB), and thus the PCE of PSC is increased to 19.15% and its humidity stability is significantly improved.