Enhancing the Efficiency and Stability of Perovskite Solar Cells through Gradient Energy Band Tin Oxide Electron Transport Layer Design with Graphene Quantum Dot Incorporation

The incorporation of graphene quantum dots (GQDs) with efficient charge carrier transport capability into a tin oxide (SnO2) solution and the utilization of their distinct mass properties for effective self-stratification are proposed as a method for enhancing the efficiency and stability of perovskite solar cells. By employing an antisolvent spin-coating technique, an SnO2 electron transport layer (ETL) with a gradient energy band structure is prepared. Devices based on this gradient energy band ETL exhibit an efficiency of 22.3%, whereas the efficiency of devices with a single SnO2 ETL, used as a reference, is only 19.8%. Moreover, for unencapsulated devices, an efficiency of 86% is retained after continuous testing for 1000 h at 40 °C by an AM 1.5 G lamp. Further investigation reveals that the introduction of GQDs not only forms a gradient energy band structure but also effectively passivates the defects in the SnO2 layer itself, thus ameliorating the issues of charge carrier separation and recombination during the transport process. This work presents an approach to SnO2 ETL design, not only applicable to perovskite solar cells but also offering inspiration for other optoelectronic devices.