Synergistic passivation and energy level alignment by graphene quantum dots for high performance inverted CsPbI3 perovskite solar cells

Inorganic CsPbI3 perovskite solar cells (PSCs) have garnered considerable attention due to their high thermal stability and promising application in tandem devices. However, further advancement of the performance of CsPbI3 PSCs is restricted by severe nonradiative recombination, which is related to substantial defects and mismatched energy levels. Herein, the versatile graphene quantum dots (GQDs) are introduced to modify the CsPbI3 surface to improve interface contact and mitigate energy loss. GQD modification can not only effectively passivate surface defects via coordinating with the undercoordinated Pb2+ but also improve energy level alignment, contributing to efficient charge extraction and suppression of nonradiative recombination. Consequently, GQDs-based inverted CsPbI3 devices deliver a champion power conversion efficiency (PCE) of 18.98% with a high open-circuit voltage (VOC) of 1.141 V and are greatly superior to the control device obtaining a poor PCE of 13.29% with a VOC of 0.986 V. Moreover, GQDs can form a protective layer at the perovskite interface to resist external invasion, significantly boosting the device stability. Our findings establish the promising application of GQD modification as a compelling strategy for achieving high performance inorganic photovoltaic devices.