Impact of Ligands on the Performance of PbS Quantum Dot Visible-Near-Infrared Photodetectors

Solution-processed lead sulfide quantum dots (PbS QDs) are an excellent candidate for photodetector applications because they exhibit broadband absorption, a wide range of tuneable bandgaps, high stability in air, and mechanical flexibility. However, a crucial criterion for the fabrication of high-performance photodetectors is the selection of the ligands, which can facilitate charge carrier transport between the PbS QDs and passivate the surface defects. In this work, the authors have studied the effect of traps on the performance of PbS QD photodetectors that are fabricated using different types of ligands, using intensity-dependent photoresponse dynamics. The best devices with lead halide ligands show a dark current density of 5 x 10(-9) A cm(-2) at -0.2 V, which is one of the lowest values reported thus far for solution-processed PbS QD-based photodetectors. Moreover, these devices show a high linear dynamic range (approximate to 90 dB) and high detectivity (>10(13) Jones), in addition to an f(-3 dB) of greater than 100 kHz without the application of an external voltage bias at a wavelength of 784 nm. These results suggest that with an appropriate selection of ligands, solution-processed photodetectors with a lower density of traps and a better device performance can be fabricated.