Electrolyte-Gated Field Effect Transistor to Probe the Surface Defects and Morphology in Films of Thick CdSe Colloidal Nanoplatelets

The optical and optoelectronic properties of colloidal quantum dots strongly depend on the passivation of their surface. Surface states are however difficult to quantify using optical spectroscopy and techniques based on back gated field effect transistors are limited in the range of carrier density that can be probed, usually significantly below one charge carrier per particle. Here we show that electrolyte gating can be used to quantitatively analyze the increase of defects in a population of nanoparticles with increasing surface irregularities. We illustrate this method using CdSe nanoplatelets that are grown in their thickness using low temperature layer-by-layer method. Spectroscopic analysis of the samples confirm that the nanoplatelet thickness is controlled, on average, with atomic precision, but structural analysis with transmission electron microscopy shows that the number of surface defects increases with the nanoplatelet thickness. The amount of charge defects is probed quantitatively using el...