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

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 CH 3 NH 3 PbBr 3 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.

Mechanisms of Spontaneous and Amplified Spontaneous Emission in CH3NH3PbI3 Perovskite Thin Films Integrated in an Optical Waveguide

“…According to data published by other authors [64], B ranges between 2×10 −11 and 1.4×10 −10 cm 3 s −1 , so we believe that our assumptions above provides realistic results. Finally, D can be calculated as 1/N 0 τ f , where τ f is a formation time for excitons (approximately 1 fs), and hence D = 10 −4 cm −3 s −1 , in agreement with experimental data reported by other authors [28]. In these conditions, DK B.…”

“…4(c)] due to the finite density of states in the first case. Similar analysis carried out on passivated CH 3 NH 3 PbBr 3 perovskite thin films also concluded that excitons play a major role in the PL spectrum, which is even underestimated by the population predicted by Saha's equation [28].…”

“…Similarly to the case of the absorption spectrum, PL spectra (waveguided) also consist of two components ascribed to exciton and free-carrier recombination, both populations being in thermal equilibrium at room temperature according to Saha's equation [28], as schematically illustrated in Fig. 4(b).…”

“…However, despite the high interest in the topic with a significant amount of works published in recent years, the underlying mechanisms of the amplified spontaneousemission (ASE) process in MHP materials are not completely understood as compared to the case of other semiconductors, which is one of the main goals of this paper. There are several works devoted to the photophysics responsible for PL [24][25][26], the nonradiative losses in traps limiting the optical gain [9,27], or the role of excitons in PL generation [28]. However, it is still an open question about the physical mechanism of optical gain, a prerequisite for lasing.…”

X-Ray-Induced Modification of the Photophysical Properties of MAPbBr3 Single Crystals

“…The spectrum of the pristine sample (black curve) shows the typical Wannier-Mott excitonic peak (here referred to as T1) generally observed in the absorption spectrum of this material. 34 , 35 T1 disappears as soon as the first X-ray dose is delivered, revealing the band-to-band absorption edge and a new peak at lower energies (T2), which increases proportionally to the absorbed dose. This effect cannot be ascribed to sample aging, as demonstrated by the consistency in time of the SPS spectra of a control sample ( Figure 1 b), which was not exposed to X-ray radiation.…”