Defect passivation and electrical conductivity enhancement in perovskite solar cells using functionalized graphene quantum dots

Organic-inorganic halide perovskites have been intensively investigated as potential photovoltaic materials due to their exceptional optoelectronic properties and their successful applications in perovskite solar cells (PSCs). However, a large number of defect states still exist in the PSCs so far and are detrimental to their power conversion efficiencies (PCEs) and stability. Here, an effective strategy of incorporating single-crystalline graphene quantum dots (GQDs) into the perovskite films is proposed to passivate the defect states. Intriguingly, the GQD-modified perovskite films exhibit purer phase structure, higher quality of morphology, and higher electrical conductivity when compared with the control perovskite films. All of the advantages caused by the incorporation of the GQDs lead to fast carrier separation and transport, long carrier lifetime, and low nonradiative recombination in the PSCs based on the GQD-modified perovskite films. As a result, this kind of PSC displays an increase in all photovoltaic parameters, and its PCE shows an enhancement of more than 20% when compared with the control PSC. Moreover, this novel PSC is demonstrated to have long-term stability and resistibility against heat and moisture. Our findings provide an insight into how to passivate the defect states and enhance the electrical conductivities in the perovskites and pave the way for their further exploration to achieve higher photovoltaic performances.