BCP as Additive for Solution-Processed PCBM Electron Transport Layer in Efficient Planar Heterojunction Perovskite Solar Cells

Phenyl-C ₆₁ -butyric acid methyl ester (PCBM) doped with bathocuproine (BCP) is employed as a novel electron transport layer (ETL) for the first time. We demonstrate that this solution-processed PCBM:BCP blend ETL could significantly improve perovskite solar cell performance in a wide range of BCP doping amounts. The effect of BCP doping has been systematically investigated through a combination of characterizations, including atomic force microscopy, UV-vis absorption spectra, Kelvin probe measurement, surface photovoltage spectroscopy, impedance spectroscopy, and the contact angle test. It is found that the incorporation of BCP not only ameliorates the film formation property of PCBM and the interfacial contact but facilitates the charge transport and separation at the interface through effectively passivating the surface trap states of perovskite as well. As a result, the power conversion efficiency is improved from 7.05% to nearly doubled 13.11%, mainly benefiting from the enhanced short-circuit current density (J _sc ) of 18.96 mA/cm ² and fill factor (FF) of 73%. Solution-processed PCBM ETL with BCP as additive endows the devices with excellent performance comparable to or even better than that of traditional devices with evaporated BCP or C ₆₀ /BCP. It is also an effective and convenient approach to simplify the device fabrication procedure, with promising application in large-scale production.