The enhancement of excitonic emission crossing Saha equilibrium in trap passivated CH3NH3PbBr3 perovskite

Fabrizio Mariano,Mauro Lomascolo,Stefania D’Agostino,Armando Genco,Marco Mazzeo,Luigi Carbone,Sonia Carallo,Arianna Cretì,Giovanni Montagna

doi:10.1038/s42005-020-0309-3

Abstract

Metal-halide semiconductor perovskites have received great attention for the development of stable and efficient light emitting diodes and lasers, since they combine high charge carrier mobility and light emission spectral-purity with low-cost fabrication methods. Nevertheless, the role of excitons, free carries and trap states in perovskite light emission properties is still unclear due to their interdependence. In this paper we selectively manage trapping and light emission mechanisms by a reversible laser-assisted trap-passivation process performed on a CH3NH3PbBr3 perovskite layer, coupled to the inner modes of a high-quality micro-cavity, which only affects the radiative recombination. We show that photoluminescence is dominated by exciton radiative decay process and that trap states passivation increases the exciton gemination rate by reducing coulombic scattering of free electrons due to the ionized impurities. This picture provides a more general description than the model based on trap states-free Saha thermodynamic equilibrium between photo-generated species.

Highlights

Metal-halide semiconductor perovskites have received great attention for the development of stable and efficient light emitting diodes and lasers, since they combine high charge carrier mobility and light emission spectral-purity with low-cost fabrication methods
The sample surface has been studied by means of atomic force microscope (AFM) revealing that it consists of randomly distributed large grains with size of the order of 1 μm, as shown in Supplementary Fig. 1a of Supplementary Note 1
The X-ray diffraction (XRD) spectrum of the MAPbBr3 film is reported in Supplementary Fig. 1b of Supplementary Note 1, showing peaks corresponding to the cubic phase of MAPbBr328,34

Summary

Introduction

Metal-halide semiconductor perovskites have received great attention for the development of stable and efficient light emitting diodes and lasers, since they combine high charge carrier mobility and light emission spectral-purity with low-cost fabrication methods. Despite outstanding power conversion/external-quantum efficiencies as high as 25 and 20%, recently reached in SSCs and LEDs, respectively[5,11], the interdependence of excitons (EX), free carriers (FC), and trap states (TS) in the spontaneous emission process of metal-halide perovskites is still an open issue[18,19,20,21]. This is especially true for those perovskites with energy gap in the visible spectral range, which are more interesting for lightemitting applications (LEDs, SSLs)[20]. A method that distinctively separates the radiative from nonradiative contribution to the spontaneous emission has not been developed to date, making the analysis of EX, FC, and TS not clear

Methods

Results

Conclusion