Introduction of Graphene Nanofibers into the Perovskite Layer of Perovskite Solar Cells

Although the application of graphene-derived nanomaterials in the electron transport layer (ETL), hole transport layer (HTL), or top electrode of perovskite solar cells (PSCs) has been thoroughly studied, the effects of inserting such materials into the perovskite layer of PSCs is not well understood. In this study, pristine graphene nanofibers were introduced into the perovskite layer of PSCs for the first time. The quality of the electrospun graphene nanofibers was optimized by controlled centrifugation of graphene sheets in the precursor suspension. Under optimized conditions, the device power conversion efficiency increased from 17.51 % without graphene to 19.83 % with graphene nanofibers, representing a 13 % increase. The introduction of graphene nanofibers into the perovskite layer led to a dramatic increase in the grain size of the perovskite layer to over 2 μm, owing to improved nucleation and crystallization at the nanofiber interface, which led to much higher FF and J_sc values. The significant increases in J_sc and V_oc are attributed to the improved charge-transport properties of the graphene nanofibers with superb charge conductivity introduced into the perovskite layer. The latter was independently verified by the measured electron transport time. The stability of the device was also improved. In summary, an effective approach has been developed to improve the performance of PSCs by using pure graphene nanofibers for the first time.