Boosting Multiple Interfaces by Co-Doped Graphene Quantum Dots for High Efficiency and Durability Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs), as the most rapidly developing next-generation thin-film photovoltaic technology, have attracted extensive research interest, yet their efficiency, scalability, and durability remain challenging. α-Fe2O3 could be used as an electron transporting layer (ETL) of planar PSCs, which exhibits a much higher humidity and UV light-stability compared to TiO2-based planar PSCs. However, the photovoltaic conversion efficiency (PCE) of the Fe2O3-based device was still below 15% because of poor interface contact between α-Fe2O3 and perovskite and poor crystal quality of perovskites. In this work, we have engineered the interfaces throughout the entire solar cell via incorporating N, S co-doped graphene quantum dots (NSGQDs). The NSGQDs played remarkable multifunctional roles: (i) facilitated the perovskite crystal growth; (ii) eased charge extraction at both anode and cathode interfaces; and (iii) induced the defect passivation and suppressed the charge recombination. When assembled with a α-Fe2O3 ETL, the planar PSCs exhibited a significantly increased efficiency from 14 to 19.2%, with concomitant reductions in hysteresis, which created a new record of the PCE for Fe2O3-based PSCs to date. In addition, PSCs with the entire device interfacial engineering showed an obviously improved durability, including prominent humidity, UV light, and thermal stabilities. Our interfacial engineering methodology via graphene quantum dots represents a versatile and effective way for building high efficiency as well as durable PSCs.