Zinc oxide doped with graphene quantum dots as improved electron transport layers for planner perovskite solar cells

Zinc oxide (ZnO), a material with excellent electron mobility and a low-temperature requirement for production, is a promising option for use as an electron transport layer in perovskite solar cells (PSCs). However, it does have the drawback of having a low open-circuit voltage (VOC). Herein, to increase the VOC parameter of ZnO-based PSCs, graphene quantum dots (GQDs) are incorporated into the ZnO precursor and used as desirable ETL for PSCs. The presence of GQDs in ZnO ETL facilitated photo-electrons at the ETL/perovskite interface by reducing charge transfer resistance in this interface. Compared to the net ZnO-based PSCs, solar cells using GQD-doped ZnO as ETL have better stability, comparable JSC, higher VOC, and FF. The best GQD-doped-ZnO ETL-based PSCs recorded the highest power conversion efficiency of 20.23% with VOC of 1.130V. Meanwhile, the boosted PCE of FAPbI3-based PSCs is achieved due to the improved perovskite crystal quality, the effective defect passivation effect of GQDs at ZnO/FAPbI3 interface, and the increased electrical conductivity of ZnO ETL. In addition, the GQD-doped ETL devices showed higher ambient air stability than the devices with net ZnO ETLs.