Date of Award
Open Access Dissertation
Chemistry and Biochemistry
Andrew B. Greytak
Colloidal semiconductor quantum dots (QDs) are attractive candidates for high-efficiency solar cells and uncooled multiplexed photodetectors due to their favorable characteristics including large absorption cross-sections, size-tunable bandgap energies spanning the ultraviolet (UV) to short wave infrared, and solution processability. These QD-based optoelectronic devices operate on the basis of efficient photogenerated charge migration within QD solids and charge separation and recombination at electrical junctions, underscoring the need for (1) processing strategies that facilitate charge transport and (2) characterization techniques that robustly interrogate charge separation at QD interfaces. Here, my work on the post-synthetic processing and surface modifications of several semiconductor QDs, as well as investigations on charge transport and separation in a multitude of optoelectronic device architectures will be presented.
This thesis is divided into four parts. First, I introduce low dimensional materials and post-synthetic purification strategies en route to device fabrication. Second, I describe my work on the formation and study of novel PbS QD/epitaxial graphene/SiC (QD/EG/SiC) optoelectronic devices, where we electrically isolate and characterize previously unreported QD/SiC heterojunctions and achieve NIR responsivity due to the incorporation of NIR bandgap (~1300 nm) PbS QD films. Scanning photocurrent microscopy acquired with a home-built MATLAB GUI application reveals that the transfer length is the characteristic length scale for charge carrier collection across the QD/SiC interfaces, which allowed extraction of the QD film resistivity (~18 kΩ-cm) by analyzing the QD/SiC junction as a lumped element transmission line. Thirdly, I introduce spatially resolved Fourier transform impedance spectroscopy as a novel technique to quickly build and map the frequency response of optoelectronic devices using optical probes. My collaborative work on environmentally benign QDs will then be discussed with focus on the formulation of ligand-exchanged AgBiS2 nanocrystal inks for photoconductive devices and the development of hybrid III-V QD/2D material phototransistors for amplified NIR detection. Finally, collaborative research on the hydrophobic self-assembly and uptake of visible bandgap, fluorescent QDs onto patterned magnetic nanoparticle templates will be described.
Kelley, M. L.(2021). Colloidal Semiconductor Quantum Dots: Solution Processing and Heterostructure-Based Optoelectronics. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/6433