Tunable Photoluminescent Nitrogen-Doped Graphene Quantum Dots at the Interface for High-Efficiency Perovskite Solar Cells

The optimization of interfacial properties between the perovskite layer and the electron-transporting layer (ETL) is always a vital approach to reduce the defects for improving the photovoltaic performance of the perovskite solar cells (PSCs). Herein, nanomaterials of tunable photoluminescent nitrogen-doped graphene quantum dots (TP-N-GQDs) were prepared though a facile solid-phase microwave-assisted (SPMA) method in the presence of citric acid by adding urea as a nitrogen precursor. Leveraging the synergistic effect of N-GQDs along with the tunable photoluminescent property at the interface of PSCs proved to be an efficient strategy for enhancing the light-harvesting capability and facilitating the charge transportation simultaneously, which leads to an overall improvement of the PSC performance. Moreover, the electron-rich pyridinic nitrogen within TP-N-GQDs acted as a Lewis base, coordinating with Pb 2+ ions in perovskite and forming coordination bonds by sharing electron pairs, thereby decreasing the density of defects at the interface and the nonradiative recombination of the photogenerated carriers. Consequently, through the optimization of the nitrogen doping ratio of TP-N-GQDs, PSCs with areas of 0.09 and 1 cm 2 achieved maximum power conversion efficiencies (PCEs) of 21.98 and 17.12%, respectively. Additionally, TP-N-GQD passivation significantly enhanced the long-term stability of the device. The unencapsulated TP-N-GQD-modified device could sustain about 83% of its initial PCE afterward for 30 days of storage in air (25 ± 5 °C, RH 25 ± 5%).