High‐Performance Inverted Perovskite Solar Cells by Reducing Electron Capture Region for Electron Transport Layers

The power conversion efficiency (PCE) of inverted perovskite solar cells (i‐PSCs) is lower than that of the normal structures. The low efficiency is mainly ascribed to the inferior properties of commonly used [6,6]‐phenyl C61 butyric acid methyl ester (PCBM) electron transport layers (ETLs) such as complexity in achieving high‐quality films, low electron mobility, imperfect energy level for electron extraction, and large electron capture region. Herein, the bulk heterojunction (BHJ) ETLs composed of PCBM and polymers are developed. The electron mobility of the BHJ film is enhanced by more than three times compared with PCBM, leading to efficient electron extraction. The electron capture region of the BHJ film decreases to 1.20 × 10−18 from 3.70 × 10−17 cm−3 for PCBM due to increased relative permittivity, which reduces the trap‐assistant recombination at the interface. Meanwhile, the devices with BHJ exhibit good stability regardless of illumination and dark storage conditions owing to the more hydrophobic BHJ films and full coverage of perovskite surface, which effectively prevent the moisture permeation into the perovskite devices. It is believed that this breakthrough provides a suitable approach to improve the efficiency and stability of i‐PSCs. The performance of inverted perovskite solar cells (i‐PSCs) is significantly improved using bulk‐heterojunction electron transport layers. The high efficiency originates from reduced trap‐assistant recombination due to the shortened electron capture region, high electron mobility, and suitable energy level of electron transport layers. The ultrahigh stability is attributed to effectively prevented moisture permeation due to more hydrophobic electron transport layers.