Local Morphology Effects on the Photoluminescence Properties of Thin CsPbBr3 Nanocrystal Films

Abstract

Lead halide perovskites are emerging as extremely interesting active materials for a wide variety of optoelectronic and photonic devices. A deep understanding of their photophysics is thus fundamental in order to properly understand the origins of the materials active properties and to provide strategies for improving them. In this work, we exploit the local morphological variations in a drop-cast thin CsPbBr3 nanocrystal film to show that the aggregation of NCs has strong effects on the peak wavelengths of PL spectra, the linewidth, and the intensity of dependence on temperature. An analysis based on models that are frequently used in the literature led to completely different conclusions about the intrinsic NC emission properties extracted from spectra measured in points with different contribution of the PL from the aggregates. Our results demonstrate that extreme care has to be used in order to correctly correlate the spectral PL features with the intrinsic emission properties of lead halide perovskite NC films.

Investigation of the exciton relaxation processes in poly(9,9-dioctylfluorene-co-benzothiadiazole):CsPbI1.5Br1.5 nanocrystal hybrid polymer–perovskite nanocrystal blend

“…This anomalous behavior is qualitatively similar to previous results on formamidinium lead triiodide NCs, 10,49 ascribed to the thermal activation of exciton detrapping from surface states. We also observe that a similar temperature induced PL intensity has been recently obtained in CsPbBr 3 NCs films, 48 only in positions of the film showing strong NCs aggregation, suggesting that the exciton detrapping involves surface states of NCs aggregates. Finally, the absence of the temperature induced PL intensity increase in other films of nominally comparable NCs allows us to exclude the attribution of this effect to eventual crystalline phase transitions in the investigated temperature range.…”

“…In particular the FWHM increase it typically related to the progressive increase of exciton–phonon coupling. 48 Concerning the NCs PL intensity we observe a progressive intensity decrease up to 230 K, followed by a PL intensity increase at higher temperatures. This anomalous behavior is qualitatively similar to previous results on formamidinium lead triiodide NCs, 10,49 ascribed to the thermal activation of exciton detrapping from surface states.…”

Light Emission Properties of Thermally Evaporated CH3NH3PbBr3 Perovskite from Nano- to Macro-Scale: Role of Free and Localized Excitons

“…In order to cope with these inherent features in perovskites and improve their emission quantum yield, many strategies have been developed [21][22][23][24][25], including chemical and physical approaches to passivate non-radiative defects (usually associated with the presence of deep TSs in the bandgap), thus favoring the radiative recombination channels. We recently demonstrated [26] that the equilibrium condition between photoexcited species densities, quantitatively expressed by Saha's equation [27], can be modified by the TSs passivation obtained by irradiating the sample by means of a UV laser under wet air conditions: this results in increasing electron-hole pairing to form bound neutral states, EXs thus becoming the dominant species.…”

Formation Mechanisms and Phase Stability of Solid-State Grown CsPbI3 Perovskites

“…The metal cations are typically divalent metal ions such as Pb 2+ , Ge 2+ and Sn 2+ , while the halide anions are I − , Cl − and Br − . [ 11 ]…”