(Keynote) Electrochemistry Insights into the Development of Colloidal Quantum Dot Infrared Photodetectors

Abstract

Colloidal quantum dots may provide a cheap and versatile approach to infrared detection and light sources. Indeed, advances in the past few years have led to commercial high definition shortwave infrared imaging with PbS quantum dots as well as academic demonstrations of solution processed mid-wave thermal imaging with HgTe quantum dots, dual band detection, flexible and hyperspectral sensors.This talk will start by describing how this progress derived from insights gained by electrochemical studies of colloidal quantum dots. Following a path previously traced for conducting polymers, solution phase electrochemical reduction and spectroscopy allowed the first observation of redox stability in quantum dot states of the colloidal quantum dots. This then led to electrochemical studies in films which confirmed ambipolar stability in the lead chalcogenides. The next key electrochemistry contribution was the development of the “solid-state ligand exchange” which increased 1000-fold the charge transfer rates across quantum dots. This led to the first observation of ohmic conduction in films of quantum dots and subsequent studies of hopping transport in these materials, before photoconductivity studies and translation to solid state gating. Electrochemistry is still routinely used to extract mobility in a state resolved manner, while that has only been recently realized with solid state gating. Electrochemistry is easily coupled with spectroscopy, and this allows much information on the states and their related interband and intraband transitions. Electrochemistry and photoluminescence have even been applied to single dots microscopy in the visible, which was used to study blinking and its elimination under reducing conditions. Electrochemistry also allowed to lower the laser threshold of quantum dot films under reducing conditions and this approach is now being translated to solid state devices by others. Finally, controlled doping is essential for devices and this is another area where electrochemistry provides much insights.This talk will then briefly describe the status of infrared photodetection beyond silicon with colloidal quantum dots, and emphasize the performance metrics and potential avenue for improvements.