Solution-processed bathocuproine cathode buffer layer towards efficient planar heterojunction perovskite solar cells

Solution process boosts organic and hybrid organic-inorganic electronic devices towards low-cost, scalable and high-throughput production. Facilely solution-processed bathocuproine (sBCP) is innovatively introduced as an effective cathode buffer layer sandwiched between the electron transport layer of (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) and Ag electrode in perovskite solar cells (PSCs) with structure of "indium-tin-oxide/ poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/ CH3NH3PbI3/ PCBM/ sBCP/Ag". The effect of sBCP concentration on PSC performance is intensively investigated. Experiments show that sBCP with optimum concentration extremely favors filling voids at the perovskite/PCBM film, which improves surface morphology and ameliorates interface characteristics of PCBM/Ag. It also contributes to the enhancement of power conversion efficiency, owing to the promotion in short circuit current density and fill factor. Impressive power conversion efficiencies of 12.47% average value and 13.24% maximum value with about 60% increment in relative to the reference device without cathode buffer layer are achieved. Moreover, the incorporation of sBCP effectively blocks diffusion of Ag atoms inside the PSCs, which reasonably accounts for long-term stability of the PSCs. Our results open up an alternative approach for constructing high-performance PSCs with solution process and advancing their applications.