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

Abstract

oleic acid and oleylamine passivates the surface defects, which, however, limits the performance of the photodetector due to the low charge carrier mobility. [9,10] The introduction of CQD sensitization with low defect and lattice-matched ligands such as lead halide perovskite semiconductors and molecular lead halides, has resulted in better device performance due to the improved charge carrier transport. [6,11,12] Moreover, these devices are self-powered, that is, they do not require the application of an external voltage bias for photodetection. [13][14][15][16][17] The process of ligand optimization in these devices depends upon the size of the QDs as well. For instance, infrared PbS QD photodetectors that have peak efficiencies of around 1500 nm, and large (>7 nm) QD sizes exhibit properties, such as a cubiclike shape and dominance of (100) facets, which differs from PbS QDs with smaller (3 nm) sizes. [18][19][20] Unlike solar cells, photodetectors need to perform at low incident powers; therefore, an important criterion is the realization of devices with low trap densities. Additional requirements for the fabrication of quantum dotbased photodetector devices that show good performance and stability include type I band alignment for the shell, matched lattice constant, and appropriate interdot spacing. [15,19,[21][22][23] For instance, Syntnyk et al. demonstrated that ligand shells that have lattice parameters that are mismatched in relation to those of the core can form defective or incomplete shells due to the induced strain. [21] Bederak et al. showed that the energetic disorder increases as the interdot spacing decreases, 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 × 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 (≈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, solutionprocessed photodetectors with a lower density of traps and a better device performance can be fabricated.

Integrated PbS Colloidal Quantum Dot Photodiodes on Silicon Nitride Waveguides

“…In literature, analysis of QDPDs is mostly carried out at relatively low power levels, that is, lower than 100 mW/ cm 2 . 42,43 Few studies, if any, have addressed the powerdependent saturation of QDPDs. To assess the limits of a linear photoresponse, we first analyzed planar bottomilluminated QDPDs (BI-QDPDs).…”

“…The ensuing strong optical confinement increases the power density and the carrier generation rate within a photoactive layer positioned on top of the waveguide, possibly leading to photodetector saturation. In literature, analysis of QDPDs is mostly carried out at relatively low power levels, that is, lower than 100 mW/cm 2 . , Few studies, if any, have addressed the power-dependent saturation of QDPDs. To assess the limits of a linear photoresponse, we first analyzed planar bottom-illuminated QDPDs (BI-QDPDs).…”

Ultra‐Low Noise Level Infrared Quantum Dot Photodiodes with Self‐Screenable Polymeric Optical Window

“…Nevertheless, the device with PM6 (680 nm) was sufficiently comparable to the performance of previously reported NIR PbS-I QPDs (PD-type). [28][29][30] Similarly, the calculated (from the J-V value (Figure S13, Supporting Information) and the measured EQE max of the device with PM6 (680 nm) at 𝜆 = 525 nm demonstrated a variance of ≈<4%, which is in contrast to that of the device without PM6.…”

Two-Step Ligand-Exchange-Assisted Charge Transfer in Graphene/PbS Quantum Dots Hybrid Near-Infrared Photodetector

“…These reports intrigued the society to develop hybrid ligands comprising organic acid and metal iodide to expedite the superiorities of both surface trap state reduction and charge transport efficiency. Solution-processed PbS QDs thin films with appropriate selection of surface ligands were reported to result in low dark current density and thus high detectivity. Despite tremendous efforts devoted to increase the carrier mobility of QDs thin-film detectors, it remains fiendishly challenging to achieve charge transport among colloidal QDs due to the low electron hopping efficiency in the film matrix .…”