2, Pohang University of Science and Technology, Pohang, , Korea (the Republic of)
3, Korea Advanced Institute of Science and Technology, Daejeon, , Korea (the Republic of)
Recently, metal-halide perovskite light-emitting diodes have attracted a great attention due to not only the high efficiency but tunable color and color purity, low material cost and easy fabrication. However, use of conventional transparent conducting oxide (TCO) electrodes has limited the development of perovskite light-emitting diodes (PeLEDs) as a flexible and efficient device. We developed light-emitting diodes with a methylammonium lead bromide (MAPbBr3) emitter using metal-oxide free graphene anode (Gr-PeLEDs). The device achieved high maximum current efficiency (CEmax) = 18.8 cd/A and maximum external quantum efficiency (EQEmax) = 4.23 %, which are both higher than those of PeLEDs based on TCO electrodes. We confirmed that the use of graphene anode can avoid formation of exciton quenching sites due to the diffused metallic species from TCO anodes to the overlying layers. Reduction of exciton quenching by using the chemically inert graphene anode for the MAPbBr3 emitter which has long exciton diffusion length resulted in increase of device efficiency. In this regard, graphene is a promising anode material to solve the intrinsic problems of metal-halide perovskite emitters in terms of exciton quenching due to the low exciton binding energy. We have also fabricated highly flexible Gr-PeLEDs on PET substrate; the graphene anode withstood repeated bending (>1,000 bending cycles) and high bending strain (5.3%). Therefore, graphene enables high-efficiency flexible PeLEDs that have high color purity and low fabrication cost, which will provide practical application of next-generation flexible displays and solid-state lighting.