Interfacial defect passivation by novel phosphonium salts yields 22% efficiency perovskite solar cells: Experimental and theoretical evidence

Abstract

Abstract We modified perovskite/Spiro‐OMeTAD interface by using two novel phosphonium salts containing PF 6 − counter anion (i.e., ClTPPPF 6 and BrTPPPF 6 ). The cation and anion in phosphonium salts possess not only ionic bonds but also coordination bonds with perovskites. The anion and cation vacancies at the surface and GBs of perovskite films can be filled by phosphonium cations and PF 6 − anions, respectively, resulting in reduced defect density and prolonged carrier lifetimes. The stronger chemical interaction and accordingly better defect passivation were certified for BrTPPPF 6 than ClTPPPF 6 . As a result, the devices modified by ClTPPPF 6 and BrTPPPF 6 deliver a PCE of 21.73% and 22.15%, respectively, which far exceed 20.6% of the control device. The unsealed BrTPPPF 6 modified device maintains 98.2% of its initial efficiency value after thermal aging of 1320 h whereas merely 84.7% for the control device. 96.4% of its original efficiency was retained for BrTPPPF 6 ‐modified device after ambient exposure of 2016 h. image