Surface polarization and recombination for quasi-2D and 3D methylammonium lead bromide light emitting diodes

In the aspect of charge injection for perovskite light emitting diodes (PeLEDs), the surface charge induced capacitive effect, also coined as surface polarization, can be generated. It may severally affect the electron–hole recombination for the electroluminescence. Here, a joint experimental and theoretical study was performed in order to unravel interior mechanisms for both quasi-two dimensional (quasi-2D) and three dimensional (3D) lead-bromide perovskites [i.e., PEA2(MAPbBr3)n−1PbBr4 and MAPbBr3] based PeLEDs. We have found a negative capacitive effect at low frequencies under the application of bias voltage from 1 to 3.5 V. This is in accordance with the surface polarization induced electron–hole recombination. Such a negative capacitive effect is more remarkable for the quasi-2D PEA2(MAPbBr3)n−1PbBr4 based PeLED. From our theoretical analyses, both surface recombination volumes (α) and lifetimes (τ) of the PeLED are bias dependent. Thus, despite ultrafast time responses (i.e., pico- to nano-seconds) for exciton dynamics, our study suggests that slow time responses (i.e., milliseconds to seconds) of the surface polarization induced recombination may contribute effectively for PeLED operations. The study indicates that the surface recombination is an alternative route for the electron–hole recombination upon electrical charge injection.