Characterization of the influences of morphology on the intrinsic properties of perovskite films by temperature-dependent and time-resolved spectroscopies

Abstract

Organic-inorganic halide perovskites have attracted enormous attention owing to their promising application in photovoltaic devices. The morphology of the perovskites is the key to driving the performance of perovskite devices, which necessitates a systematic study. In this work, two typical morphologies, i.e., flake and cube, of perovskite films are fabricated, and the temperature-dependent optical absorption and photoluminescence properties of the two types of perovskite film are systematically investigated. From the temperature-dependent spectra, both exciton and phase transition temperatures of the flake film are found to be about 10 K lower than those of the cube one. Meanwhile, the influences of the morphology on the exciton binding energy, optical phonon energy and polaron binding energy are quantitatively characterized. The exciton binding of the flake film is nearly three times smaller than that of the cube one, while the phonon coupling energy and the polaron binding energy of the former are about 5 meV and 2 meV larger than those of the latter. Furthermore, the results of photoluminescence lifetime and charge separation efficiency further reveal that the charge carrier kinetics in the two kinds of perovskite films is significantly different. The current study provides a theoretical framework to understand the fundamental physics of perovskites and to promote the design and enhancement of active materials for improved optoelectronic devices.

The influence of the electron transport layer on charge dynamics and trap-state properties in planar perovskite solar cells

“…As shown in Fig. 1c and d, both lms exhibit the same dominant diffraction peaks from the (110) and (220) planes at around 14.7 and 29.0 , 30,31 respectively, which are the characteristic peaks for a tetragonal perovskite. There is no obvious difference in the XRD patterns, suggesting that the crystal structures of the perovskite lms are almost identical on TiO 2 and SnO 2 ETLs.…”

Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

“…Therefore, the authors suggested that the temperature‐dependent Г PC should reflect more accurately the scatterings of the free excitons at low temperatures in MAPbI 3 single crystals than the temperature‐dependent Г PL . The value of the LO phonon energy ( E LO = 16.1 ± 3.4 meV) obtained for MAPbI 3 single crystals is slightly larger than the one reported for MAPbI 3 thin film (≈11.5 meV), but smaller than others reported for MAPbI 3 thin film (≈25 meV), nanoplatelets (≈21 meV), and nanocubes (≈50 meV) . Meanwhile, Diab et al reported an even lower LO phonon energy of ≈4.2 meV for the MAPbI 3 single crystals which exist a sharp excitonic emission with the FWHM of only 5 meV …”

“…The exciton binding energy of the perovskites varies in a wide range from a few meV to several tens of meV as discussed above, which is not only due to the different techniques adopted and how the results interpreted but also significantly relies on the morphology and quality of the perovskite materials. In order to investigate the relationship between the morphology and the exciton binding energy for perovskites, Yu et al carried out temperature‐dependent absorption and photoluminescence experiments for two types of MAPbI 3 perovskite films with flake and cube morphologies, which are the two typical morphologies for perovskite films under current studies. The E b value of the flake perovskite was determined to be ≈41.4 meV, while that of the cube perovskite is around ≈106.7 meV.…”

“…Exciton–phonon coupling has been studied in both hybrid and all‐inorganic perovskites, with most investigations focusing on the understanding of the temperature dependence of PL linewidth broadening by such coupling . For example, Phuong et al investigated the exciton–phonon coupling in MAPbI 3 single crystals at low temperatures (15–80 K) using both temperature‐dependent photocurrent (PC) and PL spectroscopy ( Figure a) .…”

Origin of the Enhanced Photoluminescence Quantum Yield in MAPbBr3 Perovskite with Reduced Crystal Size

“…This value is smaller but on the same order of magnitude compared to previous reports. 34,35,36,37,38,39,40 According to Manser et al 32 and Christians et al 33 , the abrupt increase of w2 that is observed at an excitation density of 7•10 15 cm -3 (no 2/3~3 .6•10 10 cm -2 ) can be attributed to the process of trap filling (which competes with band filling at low excitation densities). This threshold can thus be used as a measure of the trap density in the material.…”