Enhanced Efficiency and Stability of Inverted Planar Perovskite Solar Cells With Piperazine as an Efficient Dopant Into PCBM

[6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) had been widely adopted as an electron transport layer (ETL) in inverted planar perovskite solar cells (PSCs) due to its good solubility in nonpolar solvents, and trap-passivation effect on the perovskite. But the low conductivity and electron mobility of PCBM limit the further development of PSCs. To overcome this issue, an organic small molecule piperazine incorporated into PCBM was used as the ETL of PSCs in this article. As a result, piperazine with a low doping ratio (0.5 wt.%) into PCBM can efficiently increase the electron mobility and electric conductivity of PCBM film and promote the formation of more uniform and smooth PCBM film on perovskite substrate, in the meanwhile, provide more suitable energy level alignment. Benefiting from these positive effects of piperazine, the power conversion efficiency of inverted planar PSCs is enhanced from 14.67% to 16.12%. Moreover, piperazine-based PSC without encapsulation exhibit significantly higher stability. This article provides a simple, effective, and low-lost strategy for achieving highly efficient and stable PSCs and other perovskite-based devices.