Temperature-dependent photoluminescence of lead-free cesium tin halide perovskite microplates

Abstract

Tin halide perovskites have recently attracted extensive research attention due to their similar electronic and band structures but non-toxicity compared with their lead analogues. In this work, we prepared high-quality CsSnX3 (X=Br, I) microplates with lateral sizes of around 1~4 mm by chemical vapor deposition and investigated their low-temperature photoluminescence (PL) properties. A remarkable splitting of PL peaks of the CsSnBr3 microplate is observed at low temperatures. Besides the possible structural phase transition at below 70 K, the multi-peak fittings using Gauss functions and the power-dependent saturation phenomenon suggest that the PL could also be influenced by the conversion from the emission of bound excitons into free excitons. With the increase of temperature, the peak position shows a blueshift tendency for CsSnI3, which is governed by thermal expansion. However, the peak position of the CsSnBr3 microplate exhibits a transition from redshift to blueshift at ~160 K. The full width at half maximum of CsSnX3 broadens with increasing temperature, and the fitting results imply that longitudinal optical phonons dominate the electron-phonon coupling and the coupling strength is much more robust in CsSnBr3 than in CsSnI3. The PL intensity of CsSnX3 microplates is suppressed due to the enhanced non-radiative relaxation and exciton dissociation competing with radiative recombination. According to the Arrhenius law, the exciton binding energy of CsSnBr3 is ~38.4 meV, slightly smaller than that of CsSnI3.

Noncollinear Electric Dipoles in a Polar Chiral Phase of CsSnBr3 Perovskite

“…Band-to-band photoluminescence (PL) or its absence should provide clues about the band-edge momentum- and spin-splitting induced by the spin–orbit interaction and broken inversion symmetry in phase I. The recently reported PL at low temperatures (Figure b) shows a marked departure from the trend reported in phases III, IV, and V, and agrees broadly with our own preliminary measurements in this regime. In phase I, three features are observed, with the higher energy emission attributed to free excitons and the two others to bound excitons, based on peak widths and excitation power studies .…”

“…(b) Reported PL in phase I is multipeaked and blue shifts dramatically on cooling, in stark contrast to the reported trend at higher temperatures, offering clues about the band edge electronic structure. Data from Tan et al reproduced or adapted with permission from ref . Copyright 2023 Editorial office of Chinese Physics B.…”

“…The recently reported PL at low temperatures (Figure b) shows a marked departure from the trend reported in phases III, IV, and V, and agrees broadly with our own preliminary measurements in this regime. In phase I, three features are observed, with the higher energy emission attributed to free excitons and the two others to bound excitons, based on peak widths and excitation power studies . The peak positions of all three features blue-shift substantially on cooling into phases I and II, with the free exciton peak blue-shifting nearly 200 meV down to the lowest temperature measured.…”

“…This observation of bright photoluminescence attributed to free excitons from CsSnBr 3 phase I places constraints on the electronic structure of this phase. , It was proposed that strong Rashba effects in both the valence and conduction bands of Pb­(II) halide perovskites would suppress radiative recombination by causing direct transitions to be spin-forbidden . Though such strong Rashba splitting of the valence band is not supported experimentally in Pb­(II) bromide perovskites, , the same logic would ostensibly require that the bulk Rashba effect in CsSnBr 3 is small.…”

“…CsSnBr 3 has repeatedly attracted attention since reports of its first preparation, observation of substantial electronic conductivity, and measurement of Mössbauer spectra. − Several studies sought to understand its electronic structure in light of the combination of bright luminescence, electronic conductivity, and gapless band structure in low level theoretical treatments, with modern first-principles approaches providing clarification. − Recent studies have examined CsSnBr 3 in semiconducting applications − or clarified its structure evolution and the property impacts of proximity to lone pair formation . Most recently, photoluminescence measurements revealed multipeaked emission and a large blue-shift on cooling below 70 K, and screened hybrid functional calculations aimed at improving the description of lone pairs were used to predict an unrealized polar monoclinic phase for CsSnBr 3 and CsSnI 3 with Pc symmetry …”