Dual Role of Amino-Functionalized Graphene Quantum Dots in NiO Films for Efficient Inverted Flexible Perovskite Solar Cells.

NiO has been widely used as an effective hole-transport material for inverted perovskite solar cells (PSCs), particularly flexible PSCs, owing to its low-temperature processing, low cost, and good electron-blocking ability. However, the band structure alignment between low-temperature-processed NiO and the perovskite layer is not satisfactory, resulting in reduced photovoltaic performance. Herein, we report a novel strategy to tune the NiO hole-transport layer for achieving high-performance flexible PSCs. Amino-functionalized graphene quantum dots (AGQDs) are employed in the NiO film as a dual-role additive. On the one hand, the added AGQDs can provide abundant N atoms at the modified NiO layer surface to enhance the crystallization of the perovskite film by a Lewis base-acid interaction. On the other hand, the AGQDs can optimize the band structure alignment between the NiO and perovskite layers, facilitating hole extraction at the NiO/perovskite interface. As a result, the inverted flexible PSCs exhibit a high efficiency of 18.10%, which is comparable to the values reported for the current state-of-the-art inverted flexible PSCs. In addition to good air stability, our best flexible devices have excellent mechanical stability, retaining 88% of their initial efficiency after continuously bending 1000 times. This new strategy highlights a promising way to enhance the performance of inverted flexible PSCs.