Publication

Exciton and Carrier Dynamics in Two-Dimensional Perovskites

Abstract

Two-dimensional Ruddlesden−Popper hybrid lead halide perovskites have become a major topic in perovskite optoelectronics. Here, we aim to unravel the ultrafast dynamics governing the evolution of charge carriers and excitons in these materials. Using a combination of ultrabroadband time-resolved THz (TRTS) and fluorescence upconversion spectroscopies, we find that sequential carrier cooling and exciton formation best explain the observed dynamics, while exciton−exciton interactions play an important role in the form of Auger heating and biexciton formation. We show that the presence of a longer-lived population of carriers is due to the latter processes and not to a Mott transition. Therefore, excitons still dominate at laser excitation densities. We use kinetic modeling to compare the phenethylammonium and butylammonium organic cations while investigating the stability of the resulting films. In addition, we demonstrate the capability of using ultrabroadband TRTS to study excitons in large binding energy semiconductors through spectral analysis at room temperature.

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Related concepts (32)
Exciton
An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb force. It is an electrically neutral quasiparticle that exists in insulators, semiconductors and some liquids. The exciton is regarded as an elementary excitation of condensed matter that can transport energy without transporting net electric charge. An exciton can form when a material absorbs a photon of higher energy than its bandgap. This excites an electron from the valence band into the conduction band.
World population
In demographics, the world population is the total number of humans currently living. It was estimated by the United Nations to have exceeded eight billion in mid-November 2022. It took over 200,000 years of human prehistory and history for the human population to reach one billion and only 219 years more to reach 8 billion. The human population has experienced continuous growth following the Great Famine of 1315–1317 and the end of the Black Death in 1350, when it was nearly 370,000,000.
Mott insulator
Mott insulators are a class of materials that are expected to conduct electricity according to conventional band theories, but turn out to be insulators (particularly at low temperatures). These insulators fail to be correctly described by band theories of solids due to their strong electron–electron interactions, which are not considered in conventional band theory. A Mott transition is a transition from a metal to an insulator, driven by the strong interactions between electrons.
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