Carrier-Specific Femtosecond XUV Transient Absorption of PbI2 Reveals Ultrafast Nonradiative Recombination

TL;DR

This study uses femtosecond XUV transient absorption and electron diffraction to investigate ultrafast nonradiative recombination in PbI2, revealing temperature-dependent electronic and lattice dynamics and quantifying the recombination rate.

Contribution

It introduces a combined XUV transient absorption and electron diffraction approach to study carrier dynamics in PbI2, providing new insights into ultrafast recombination mechanisms.

Findings

Nonradiative recombination occurs within picoseconds.

Recombination follows a 2nd-order kinetic model.

Recombination rate constant is 2.5x10^-9 cm^3/s.

Abstract

Femtosecond carrier recombination in PbI2 is measured using tabletop high-harmonic extreme ultraviolet (XUV) transient absorption spectroscopy and ultrafast electron diffraction. XUV absorption from 45 eV to 62 eV measures transitions from the iodine 4d core level to the conduction band density of states. Photoexcitation at 400 nm creates separate and distinct transient absorption signals for holes and electrons, separated in energy by the 2.4 eV band gap of the semiconductor. The shape of the conduction band and therefore the XUV absorption spectrum is temperature dependent, and nonradiative recombination converts the initial electronic excitation to thermal excitation within picoseconds. Ultrafast electron diffraction (UED) is used to measure the lattice temperature and confirm the recombination mechanism. The XUV and UED results support a 2nd-order recombination model with a rate constant of 2.5x10-9 cm3/s.