Photoexcitation of PbS Nanosheets Leads to Highly Mobile Charge Carriers and Stable Excitons

TL;DR

This study investigates the optoelectronic properties of solution-processed 2D PbS nanosheets, revealing high charge carrier mobility and stable excitons, making them promising for ultrathin optoelectronic devices.

Contribution

It provides detailed analysis of free charge carriers and excitons in PbS nanosheets of varying thickness using optical pump-terahertz spectroscopy, highlighting their high mobility and exciton quantum yield.

Findings

Quantum yield of excitons is large.

Charge carrier mobility ranges from 550 to 1000 cm2/Vs.

Mobility increases with nanosheet thickness.

Abstract

Solution-processable two-dimensional (2D) semiconductors with chemically tunable thickness and associated tunable band gaps are highly promising materials for ultrathin optoelectronics. Here, the properties of free charge carriers and excitons in 2D PbS nanosheets of different thickness are investigated by means of optical pump-terahertz probe spectroscopy. By analyzing the frequency-dependent THz response, a large quantum yield of excitons is found. The scattering time of free charge carriers increases with nanosheet thickness, which is ascribed to reduced effects of surface defects and ligands in thicker nanosheets. The data discussed provide values for the DC mobility in the range 550 - 1000 cm2/Vs for PbS nanosheets with thicknesses ranging from 4 to 16 nm. Results underpin the suitability of colloidal 2D PbS nanosheets for optoelectronic applications.