Charge Transport in Trap-Sensitized Infrared PbS Quantum-Dot-Based Photoconductors: Pros and Cons

Abstract

Control of quantum-dot (QD) surface chemistry offers a direct approach for the tuning of charge-carrier dynamics in photoconductors based on strongly coupled QD solids. We investigate the effects of altering the surface chemistry of PbS QDs in such QD solids via ligand exchange using 3-mercaptopropionic acid (MPA) and tetrabutylammonium iodide (TBAI). The roll-to-roll compatible doctor-blade technique was used for the fabrication of the QD solid films as the photoactive component in photoconductors and field-effect phototransistors. The ligand exchange of the QD solid film with MPA yields superior device performance with higher photosensitivity and detectivity, which is due to less dark current and lower noise level as compared to ligand exchange with TBAI. In both cases, the mechanism responsible for photoconductivity is related to trap sensitization of the QD solid, in which traps are responsible of high photoconductive gain values, but slow response times under very low incident optical power (<1 pW). At medium–high incident optical powers (>100 pW), where traps are filled, both MPA- and TBAI-treated photodevices exhibit similar behavior, characterized by lower responsivity and faster response time, as limited by the mobility in the QD solid.

Citric Acid Capped CdS Quantum Dots for Fluorescence Detection of Copper Ions (II) in Aqueous Solution

“…Generally, the blue shift of absorption peak was caused by quantum confinement [58]. The absorption edge, obtained by the intersection of the sharply decreasing region of the spectrum with the baseline, corresponds to band gap of 2.84 eV [47]. As shown in Figure 5b, according to the linear between ( αhυ ) 2 and photon energy ( hυ ) [59,60,61], the band energy was determined to be 2.81 eV.…”

“…Besides, semiconductor QDs can be further modified by surface ligands and therefore obtain specific fluorescent prober. So far, these surface ligands with functional groups, including citrate [42], L-cysteine [43,44], cysteamine [45,46], 3-mercaptopropionic acid [47], thioglycolic acid [48], glutathione [49] and peptide [50], which have been studied in CdS QDs modification and analytical application. Therefore, it could be expected that surface ligands modified CdS QDs as fluorescence probe for detecting Cu 2+ show promise.…”

Ligand-Length Modification in CsPbBr3 Perovskite Nanocrystals and Bilayers with PbS Quantum Dots for Improved Photodetection Performance

“…Tandem photodevices integrating two stacked films of CsPbBr 3 PNCs and PbS QDs were fabricated by using similar procedures described above. PbS QDs were synthetized according to a procedure described in our previous publications [ 16 , 29 ] in which a Schottky heterostructure was built by Doctor Blade to operate at telecom wavelengths (see emission and absorption spectra in Figure S1 ).…”

“…Such films were prepared by doctor blading technique using a well purified solution of CsPbBr 3 PNCs. In thin films deposited by layer-stacking of PNCs, the dominant transport mechanism can be assimilated to carrier hopping because of the three-dimensional electronic coupling between PNCs [ 29 ]. The Schottky-heterostructure photodevices were fabricated with/without MPA ligand exchange to study the differences in their electro-optical properties.…”

Preparation of Tin Oxide Quantum Dots in Aqueous Solution and Applications in Semiconductor Gas Sensors

“…Thus, in recent decades, QDs have attracted a lot of attention. For example, Alberto prepared PbS QDs for photoconductors, in which the control of surface chemistry offered a direct approach for the tuning of charge carrier dynamics based on strongly coupled QD solids [ 1 ]. Ternary alloy PbCdS QDs were explored as photosensitizers for quantum dot sensitized solar cells [ 2 ].…”