Charge Carrier Relaxation in Colloidal FAPbI3 Nanostructures Using Global Analysis

Carolina Villamil Franco,Thomas Gustavsson,Elsa Cassette,Christian Cornaggia,Benoît Mahler

doi:10.3390/nano10101897

Abstract

We study the hot charge carrier relaxation process in weakly confined hybrid lead iodide perovskite colloidal nanostructures, FAPbI3 (FA = formaminidium), using femtosecond transient absorption (TA). We compare the conventional analysis method based on the extraction of the carrier temperature (Tc) by fitting the high-energy tail of the band-edge bleach with a global analysis method modeling the continuous evolution of the spectral lineshape in time using a simple sequential kinetic model. This practical approach results in a more accurate way to determine the charge carrier relaxation dynamics. At high excitation fluence (density of charge carriers above 1018 cm−3), the cooling time increases up to almost 1 ps in thick nanoplates (NPs) and cubic nanocrystals (NCs), indicating the hot phonon bottleneck effect. Furthermore, Auger heating resulting from the multi-charge carrier recombination process slows down the relaxation even further to tens and hundreds of picoseconds. These two processes could only be well disentangled by analyzing simultaneously the spectral lineshape and amplitude evolution.

Highlights

Thanks to their outstanding properties, lead halide perovskites have emerged as extremely promising low-cost processing materials for several optoelectronic applications as solar cells [1,2], photo-detectors [3,4], light-emitting diodes [5,6] and lasers [7,8]
Using the classical tail-fitting method to extract the carrier temperature Tc from the transient absorption (TA) spectra and plotting the energy-loss rate versus this temperature allows to compare the cooling dynamics between different samples or, different initial excess energies for a given sample [13,14], we found it quite sensitive to the energy range used for the fit (Figure 2a)
We have investigated the hot charge carrier cooling dynamics of colloidal FAPbI3 nanostructures in the weak confinement regime. These results show that the evolution of the lineshape and signal amplitude in time as obtained from global TA data analysis allows us to disentangle the different processes behind the charge carrier relaxation and recombination in these samples

Summary

Introduction

Thanks to their outstanding properties, lead halide perovskites have emerged as extremely promising low-cost processing materials for several optoelectronic applications as solar cells [1,2], photo-detectors [3,4], light-emitting diodes [5,6] and lasers [7,8] For all these applications, it is of main importance to characterize the rate at which hot charge carriers relax to the band-edge (cooling). Nanocrystal samples are susceptible to present inhomogeneous spectral lineshapes due to size dispersion, which can artificially induce higher carrier temperatures All of those imprecisions in the determination of Tc will have a direct impact on the energy-loss rate values, proportional to dTc/dt, used to compare one sample to another in terms of composition or confinement effects [9]

Methods

Results

Discussion

Conclusion