Incorporating an Inert Polymer into the Interlayer Passivates Surface Defects in Methylammonium Lead Halide Perovskite Solar Cells

The hysteresis effect and instability are important concerns in hybrid perovskite photovoltaic devices that hold great promise in energy conversion applications. In this study, we show that the power conversion efficiency (PCE), hysteresis, and device lifetime can be simultaneously improved for methylammoniumlead halide (CH3NH3PbI3‐xClx) solar cells after incorporating poly(methyl methacrylate) (PMMA) into the PC61BM electron extraction layer (EEL). By choosing appropriate molecular weights of PMMA, we obtain a 30 % enhancement of PCE along with effectively lowered hysteresis and device degradation, adopting inverted planar device structure. Through the combinatorial study using Kelvin probe force microscopy, diode mobility measurements, and irradiation‐dependent solar cell characterization, we attribute the enhanced device parameters (fill factor and open circuit voltage) to the surface passivation of CH3NH3PbI3‐xClx, leading to mitigating charge trapping at the cathode interface and resultant Shockley‐Read‐Hall charge recombination. Beneficially, modified by inert PMMA, CH3NH3PbI3‐xClx solar cells display a pronounced retardation in performance degradation, resulting from improved film quality in the PC61BM layer incorporating PMMA which increases the protection for underneath perovskite films. This work enables a versatile and effective interface approach to deal with essential concerns for solution‐processed perovskite solar cells by air‐stable and widely accessible materials. Danger danger! High voltage! Incorporating the inert PMMA into the fullerene based electron extraction layer not only suppresses unfavorable hysteresis in perovskite solar cells but also enhances the device stability. The improvements can be primarily ascribed to surface passivation with the functional groups in PMMA and the formation of a more compact and dense layer together with PCBM to improve protection of perovskite films.