Engineering the Surface Chemistry of Colloidal InP Quantum Dots for Charge Transport

Abstract

Colloidal InP quantum dots (QDs) have emerged as potential candidates for constructing nontoxic QD-based optoelectronic devices. However, charge transport in InP QD thin-film assemblies has been limitedly explored. Herein, we report the synthesis of 8 nm edge length (6.5 nm in height), tetrahedral InP QDs and study charge transport in thin films using the platform of the field-effect transistor (FET). We design a hybrid ligand-exchange strategy that combines solution-based exchange with S2- and solid-state exchange with N3- to enhance interdot coupling and control the n-doping of InP QD films. Further modifying the QD surface with thin, thermally evaporated Se overlayers yields FETs with an average electron mobility of 0.45 cm2 V-1 s-1, 10 times that of previously reported devices, and a higher on-off current ratio of 103-104. Analytical measurements suggest lower trap-state densities and longer carrier lifetimes in the Se-modified InP QD films, giving rise to a four-time longer carrier diffusion length.