Enhanced Radiative Recombination of Excitons and Free Charges Due to Local Deformations in the Band Structure of MAPbBr₃ Perovskite Crystals

Abstract

We have imaged the emissions from excitons and free charges in a methylammonium lead bromide perovskite (MAPbBr 3 ) crystal. In a direct band gap semiconductor, dynamics of excited electrons and holes in hybrid lead-halide perovskites is rather complex because of the formation of excitons and the presence of traps and structural inhomogeneities. A recent report by Nah et al.

Nature of the different emissive states and strong exciton–phonon couplings in quasi-two-dimensional perovskites derived from phase-modulated two-photon micro-photoluminescence spectroscopy

“…Previous measurements of PL microscopy in bulk crystals of MPB have shown significant variation in the emission intensity and spectra. 37,38,49 It is interesting to investigate if such inhomogeneity is also present in the quasi-2d crystals. We have used spatially resolved 2PPL spectroscopy to study the spatial variations in the emission.…”

“…The number of electrons (n e ) or holes (n h ), excited by two phase-modulated beams with frequency difference a shows modulations at a and 2 a , and the relative amplitudes are given by the expression, n e = n h 3 + 4 cos( a t) + cos(2 a t). 37 The derivation of the expression is given in the Supporting Information. As the excitonic recombination is directly proportional to the population of bound e-h pairs, which itself scales linearly with n e , the PL from excitons is given by the same expression.…”

“…A detailed theoretical discussion of the recombination processes that contribute to different orders of modulations is given in ref. 37.…”

“…36 This approach has also been used to investigate the different recombination processes in organo-halide semiconductors (mainly crystals of MPB) based on the order of the recombination. 37 In this contribution, we have carried out spatially resolved phase-modulated two-photon photoluminescence spectroscopy (2PPL), and temperature-dependent 2PPL to understand the underlying mechanisms that contribute to the emission and other relevant photophysical This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.…”

Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes

“…This method is an extension of 2D electronic spectroscopy, but uses photocurrent generated in a device as the measured signal when illuminated by two pairs of pulses of light in a pump and probe setup for following the nonlinear response of the excited photodiode (see Methods section). In distinction to our method for nonlinear imaging of photocurrent for identifying recombination mechanisms 34,35 , where the amplitude of the nonlinear incoherent response is used, here the phase of the photocurrent is extracted by varying the interpulse time delays. This has been shown to account for the coherent nonlinear interactions in this type of spectroscopic measurement 36,37 .…”