Redox-active Eu2O3 nanoflakes as a buffer layer for inverted CsPbI2Br perovskite solar cells with enhanced performance

Abstract

Solution processed CsPbX₃ films usually present a high content of Pb⁰ clusters, acting as significant defects on the perovskite surface. Conventional electron transport materials, including PC₆₁BM, TiO₂, ZnO, SnO₂ and Nb₂O₅, can hardly passivate these defects. In this work, few-layered Eu₂O₃ nanoflakes (nano-Eu₂O₃) are prepared, which exhibit much higher redox activity towards Pb⁰/I⁰ than the commercial Eu₂O₃ powder. When nano-Eu₂O₃ is introduced as the buffer layer between the CsPbI₂Br and PC₆₁BM layers in inverted perovskite solar cells (PeSC), the devices deliver remarkably improved photovoltaic performance with an average power conversion efficiency (PCE) of 13.47% and a champion PCE of 14.09%, which is much superior to the control devices without nano-Eu₂O₃ (9.74/11.03%). A series of mechanism studies reveal that the addition of nano-Eu₂O₃ buffer layer enables not only more efficient hole-blocking but also remarkably enhanced defect passivation at the perovskite/PC₆₁BM interface, both of which result in significantly reduced interfacial charge recombination. Besides, we show that the devices with nano-Eu₂O₃ exhibit obviously improved thermal stability with >90% PCE remaining after 400 h of thermal aging at 80 °C.