Surface Passivation of Perovskite by Hole-Blocking Layer toward Efficient and Stable Inverted Solar Cells

Inverted (p-i-n) perovskite solar cells (PSCs) are advantageous in terms of easy fabrication, low-temperature processibility, negligible hysteresis, and excellent compatibility with the tandem devices in comparison with the regular (n-i-p) counterparts. Hole-blocking layer is crucial for efficient electron transport of inverted PSCs, and only a single hole-blocking layer of bathocuproine (BCP) is used typically. Herein, bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO) with a deep highest occupied molecular orbital (HOMO) energy level is incorporated atop of perovskite film as an auxiliary hole-blocking layer, resulting in an enhanced electron transport of inverted PSC devices. The P=O group within DPEPO can coordinate with Pb 2+ cations of perovskite, leading to passivation of surface defects of perovskite. Besides, incorporation of DPEPO hole-blocking layer prohibits undesired hole transport from perovskite to PCBM electron transport layer (ETL), thus suppressing non-radiative electron–hole recombination. As a result, combined with BCP hole-blocking layer, inverted PSC devices based on double hole-blocking layers exhibit a decent power conversion efficiency (PCE) of 24.17% with a high open-circuit voltage ( V oc ) of 1.15 V which dramatically surpasses that based on single hole-blocking layer (22.26%). Moreover, incorporation of hydrophobic DPEPO helps to improve the ambient and thermal stabilities of inverted PSC devices.