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

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 CsPbI3 perovskite. All these issues result in large losses in open-circuit voltage (V-oc) and fill factor (FF), and thus, CsPbI3 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 CsPbI3 perovskite film. Concomitantly, residual EC passivates the uncoordinated Pb2+ defects by synergistical chemical interaction of C equivalent to N and C=O groups, and energy level arrangement at the CsPbI3/P3HT interface is also optimized. As a result, the PCE of P3HT-based CsPbI3 PSC is improved to 18.46% from 17.33% of the control device. The unencapsulated CsPbI3 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 CsPbI3 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.