Effects of ethylenediamine on the intrinsic photoresponse of PbS quantum dots

We examine the intrinsic recombination dynamics of PbS quantum dots (QDs) functionalized with ethylenediamine (EDA) and compare it to that of the same QDs functionalized with ethane-1,2-dithiol (EDT). The recombination dynamics were studied as a function of temperature, pressure, and excitation intensity using asynchronous optical sampling (ASOPS). Only for EDA functionalization, we find that under vacuum at room temperature roughly 40% of the total photocurrent decays with a fast lifetime of approximately 100 picoseconds. Intensity-dependent studies indicate that the remaining recombination processes are consistent with trap-assisted Auger recombination mechanisms. Temperature-dependent measurements suggest that the fast 100 ps component is governed by a phonon-assisted decay process. Exploiting such processes could be beneficial for realizing GHz photodetection with PbS QDs.