Impact of surface polarization and ion accumulation on electroluminescence for methylammonium lead bromide light emitting diodes

Abstract

The coexistence of polarization and mobile ions is an extraordinary property for hybrid perovskites, as they are proven critical for charge generation and transport. There is a lack of study to elucidate the slow responses of surface polarization and ion accumulation on the electroluminescence (EL) for perovskite light emitting diodes (PeLEDs). Here, we adopt ac-field impedance spectroscopy combined with in situ EL measurements for the study of surface recombination, when a prototypical methylammonium lead bromide (CH₃NH₃PbBr₃) PeLED operates at working conditions. We have found that the surface polarization due to charges and ions has remarkable impact on EL characteristics such as the illumination intensity, full width at half maximum (FWHM), and emissive peak. Such a phenomenon can be explained by the slow surface polarization relaxation and the ion vacancy-polarization interaction. Both of them promote surface band-to-band and trap-assist recombination, while giving rise to the EL intensity. This surface science study is merit for understanding the role of surface polarization and ion accumulation for the EL generation in PeLEDs.