Tunable ionic conductivity and photoluminescence in quasi-2D CH3NH3PbBr3 thin films incorporating sulphur doped graphene quantum dots

Abstract

Ion migration in hybrid halide perovskites is ubiquitous in all conditions. However, the ionic conductivity can be manipulated by changing the material composition, operating temperature, light illumination, and applied bias as well as the nature of the interfaces of the devices. There have been various reports on electron ion coupling in hybrid perovskite semiconductors which gives rise to anomalous charge transport behavior in these devices under an applied bias. In this investigation, we have synthesized a mixture of 2D/3D perovskites by incorporating sulphur-doped graphene quantum dots (SGQDs) and demonstrated that the optical and electrical properties of the hybrid system can be tuned by controlling the ion conductivity through the active layer. It has been observed that the recombination resistance in undoped CH₃NH₃PbBr₃ perovskites follows an anomalous behavior while the doped CH₃NH₃PbBr₃ perovskite shows a monotonic increase with increasing applied bias due to reduced ionic conductivity. SGQDs at the grain boundaries of 2D/3D perovskites prohibit ion migration through the active layer, and therefore the electronic-ionic coupling is reduced. This results in increased recombination resistance with increasing applied bias.