Joshua J. Choi
· Associate Professor of Chemical Engineering Associate Professor of Physics (by courtesy)VerifiedUniversity of Virginia · Materials Science and Engineering
Active 2009–2026
About
Joshua J. Choi, Ph.D., is an Associate Professor in the Department of Chemical Engineering and holds a courtesy appointment as Associate Professor in the Department of Physics at the University of Virginia. He earned his Bachelor of Engineering degree from Cooper Union in 2006, followed by a Ph.D. from Cornell University in 2012. After completing his doctoral studies, he conducted postdoctoral research at Columbia University until 2014. Professor Choi has been recognized with several awards, including the NASA Early Career Faculty Award and the Virginia Space Grant Consortium New Investigator Award, both received in 2015. His professional affiliation with the Choi Laboratory for Optoelectronic Materials reflects his research focus on optoelectronic materials, contributing to advancements in this field through his academic and research activities at the University of Virginia.
Research topics
- Chemistry
- Inorganic chemistry
- Materials science
- Physics
- Optoelectronics
- Crystallography
- Chemical physics
- Organic chemistry
- Composite material
- Condensed matter physics
- Thermodynamics
- Optics
- Metallurgy
- Computational chemistry
- Radiochemistry
Selected publications
Materials Research Express · 2026-01-21
articleOpen accessSenior authorAbstract X-ray imaging has found applications in many aspects of modern society. Highly sensitive imaging detectors with simple manufacturing methods can increase the deployment of detectors and enable low-dose imaging. In this work, we report on the impact of the solid-state synthesis conditions on the scintillator properties of the lead halide perovskite CsPbCl 3 :Yb. We optimize the synthesis conditions to maximize the light output when exposed to a radiography-relevant spectrum of x-rays. Using optimized conditions, we produced a scintillator powder with light output above 40,000 photons MeV −1 , rivaling commercially available radiography scintillators. The imaging characteristics are measured for scintillator screens comprised of powder dispersed in a polymer matrix and find the spatial resolution acceptable for general radiography. We conclude that CsPbCl 3 :Yb produced in this manner can be used for low frame rate radiography in conjunction with silicon photodetectors and has potential for much higher quantum efficiency imaging if used in conjunction with an NIR optimized photosensor.
Journal of the Physical Society of Japan · 2025-02-07 · 1 citations
articleSinglet-Fission Dynamics Modified through Templated Organic Semiconductor Crystallization
ChemRxiv · 2025-10-15
preprintSinglet fission (SF) is a process of multiexciton generation in molecular semiconductor materials that holds promise for improving light-to-charge conversion efficiencies in photovoltaic devices. Molecular packing structure is well-known to impact the electronic coupling that underlies triplet-pair generation, as well as pair separation and triplet transport that occur through singlet fission, ultimately affecting the potential to increase conversion efficiencies in light-harvesting devices. We previously demonstrated that templating the crystallization of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) films on a series of lead-halide perovskites provides a means to control intermolecular packing and alter the kinetics of triplet-pair separation and recombination. Here we contrast triplet transport with the ultrafast interconversion of the singlet exciton to the correlated triplet pair and the dependence of these processes on template-modified crystal packing. We observe that rate constants for the conversion of singlet excitons to correlated triplet pairs likewise are sensitive to the template structure but with a trend that is anticorrelated with those for triplet-pair separation and triplet-triplet annihilation. This observation is consistent with the divergent requisite frontier orbital overlap symmetries of adjacent chromophores that underlie the electronic coupling associated with the generation of triplet pairs and the subsequent triplet transport. We examine how the template-dependent packing structures, as determined by molecular dynamics simulations of a film-template interface, alter figures of merit for electronic interactions (estimated by frontier-orbital overlaps) that underlie each step of the SF mechanism. Our results demonstrate that templating is a general platform for tuning the relative rates of deactivation of correlated triplet pairs in SF-active materials with the potential to favor higher triplet-pair yields or for assisting singlet-mediated triplet-transfer mechanisms without structural modification of the SF-active chromophore.
Singlet-Fission Dynamics Modified through Templated Organic Semiconductor Crystallization
ChemRxiv · 2025-11-12
articleSinglet fission (SF) is a process of multiexciton generation in molecular semiconductor materials that holds promise for improving light-to-charge conversion efficiencies in photovoltaic devices. Molecular packing structure is well-known to impact the electronic coupling that underlies triplet-pair generation, as well as pair separation and triplet transport that occur through singlet fission, ultimately affecting the potential to increase conversion efficiencies in light-harvesting devices. We previously demonstrated that templating the crystallization of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) films on a series of lead-halide perovskites provides a means to control intermolecular packing and alter the kinetics of triplet-pair separation and recombination. Here we contrast triplet transport with the ultrafast interconversion of the singlet exciton to the correlated triplet pair and the dependence of these processes on template-modified crystal packing. We observe that rate constants for the conversion of singlet excitons to correlated triplet pairs likewise are sensitive to the template structure but with a trend that is anticorrelated with those for triplet-pair separation and triplet-triplet annihilation. This observation is consistent with the divergent requisite frontier orbital overlap symmetries of adjacent chromophores that underlie the electronic coupling associated with the generation of triplet pairs and the subsequent triplet transport. We examine how the template-dependent packing structures, as determined by molecular dynamics simulations of a film-template interface, alter figures of merit for electronic interactions (estimated by frontier-orbital overlaps) that underlie each step of the SF mechanism. Our results demonstrate that templating is a general platform for tuning the relative rates of deactivation of correlated triplet pairs in SF-active materials with the potential to favor higher triplet-pair yields or for assisting singlet-mediated triplet-transfer mechanisms without structural modification of the SF-active chromophore.
Chemistry of Materials · 2024-07-19 · 5 citations
articleOpen accessUsing complementary experimental measurements and computational predictions of spectroscopic measurements (EXAFS, XANES, and UV–vis), we have determined the identity of the most stable iodoplumbate species in dilute lead halide perovskite precursor solutions. We have determined which species are most likely to be thermodynamically stable compared to others that are unstable or metastable. Condensed phase ab initio models were constructed, and the resulting ensembles were used to directly compare the computed signals to the experimental results of the EXAFS, XANES, and UV–vis spectra of PbI2:MAI in DMF. The results of this study suggest that only Pb2+, PbI+, and PbI2 are dominant in the dilute lead perovskite precursor solutions as thermodynamically stable entities. Our interpretation of the relative stability of iodoplumbate species in solution, based on an analysis of EXAFS and XANES spectra, provides critically important new insight into the species most likely to be responsible for crystal nucleation and growth in these materials. This insight will have a significant consequence on the broad scientific community and will necessitate the reinterpretation of peaks in the UV–vis spectra of lead halide perovskite precursor solutions.
The Journal of Physical Chemistry C · 2024-11-21 · 1 citations
articleOpen accessSenior authorCorrespondingWe contrast the switching of photoluminescence (PL) of PbS quantum dots (QDs) cross-linked with photochromic diarylethene molecules with different end groups, 4,4′-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (1C) and 4,4′-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenethiocarboxylic acid] (2T). Our results show that the QDs cross-linked with the carboxylic acid end group molecules (1C) exhibit a greater amount of switching in photoluminescence intensity compared to QDs cross-linked with the thiocarboxylic acid end group (2T). We also demonstrate that regardless of the molecule used, greater switching amounts are observed for smaller quantum dots. Varying these parameters allows for the fabrication of photoswitches with tunable PL change. We relate these observations to the differences in the HOMO energy levels between the QDs and the photochromic molecules. Our findings demonstrate how the size of the QDs and the energy levels of the linker ligands influences the charge tunneling rate and thus the PL switching performance in tunneling-based photoswitches.
Synthesis of Bis-Thioacid Derivatives of Diarylethene and Their Photochromic Properties
ACS Omega · 2024-11-18 · 2 citations
articleOpen accessDiarylethenes (DAEs) are an important class of photoswitchable compounds that typically undergo reversible photochemical conversions between the open and closed cyclized forms upon treatment with UV light or visible light. In this study, we introduced thioacid functional groups to several photochromic dithienylethene (DTE) derivatives and established a method that can be used to prepare these photoswitchable thioacids. Four thioacid-functionalized diarylethene derivatives were synthesized through the activation of carboxylic acids with N-hydroxysuccinimide, followed by reactions with sodium hydrosulfide with yields over 90%. These derivatives exhibited reversible photoswitching and photochromic properties upon treatment with ultraviolet (UV) and visible lights. The thioacid groups on these compounds can act as reaction sites for attaching other desirable functionalities. The photochromic properties of these new derivatives were characterized by using ultraviolet–visible (UV–vis) spectroscopy. The photocyclizations of one of the derivatives and its potassium salt were also characterized by using nuclear magnetic resonance (NMR) spectroscopy. The anions of the thioacid formed water-soluble photochromic systems, and their applications as colorimetric sensors in agarose hydrogels were demonstrated.
arXiv (Cornell University) · 2024-02-24
preprintOpen accessTwo-dimensional hybrid organic-inorganic perovskites (HOIPs) have emerged as promising materials for light-emitting diode applications. In this study, by using time-of-flight neutron spectroscopy we identified and quantitatively separated the lattice vibrational and molecular rotational dynamics of two perovskites, butylammonium lead iodide (BA)$_{2}$PbI$_{4}$ and phenethyl-ammonium lead iodide (PEA)$_{2}$PbI$_{4}$. By examining the corresponding temperature dependence, we found that the lattice vibrations, as evidenced by neutron spectra, are consistent with the lattice dynamics obtained from Raman scattering. We revealed that the rotational dynamics of organic molecules in these materials tend to suppress their photoluminescence quantum yield (PLQY) while the vibrational dynamics did not show predominant correlations with the same. Additionally, we observed photoluminescence emission peak splitting for both systems, which becomes prominent above certain critical temperatures where the suppression of PLQY begins. This study suggests that the rotational motions of polarized molecules may lead to a reduction in exciton binding energy or the breaking of degeneracy in exciton binding energy levels, enhancing non-radiative recombination rates, and consequently reducing photoluminescence yield. These findings offer a deeper understanding of fundamental interactions in 2D HOIPs and could guide the design of more efficient light-emitting materials for advanced technological applications.
RSC Advances · 2024-01-01 · 8 citations
articleOpen accessSenior authorCorrespondingWe investigate switching of photoluminescence (PL) from PbS quantum dots (QDs) crosslinked with two different types of photochromic diarylethene molecules, 4,4'-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (1H) and 4,4'-(1-perfluorocyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (2F). Our results show that the QDs crosslinked with the hydrogenated molecule (1H) exhibit a greater amount of switching in photoluminescence intensity compared to QDs crosslinked with the fluorinated molecule (2F). With a combination of differential pulse voltammetry and density functional theory, we attribute the different amount of PL switching to the different energy levels between 1H and 2F molecules which result in different potential barrier heights across adjacent QDs. Our findings provide a deeper understanding of how the energy levels of bridge molecules influence charge tunneling and PL switching performance in QD systems and offer deeper insights for the future design and development of QD based photo-switches.
Ytterbium-doped cesium lead chloride perovskite as an x-ray scintillator with high light yield
2023-06-15
articleOpen accessSenior authorHerein, we evaluate Yb3+ doped CsPbCl3 as a bright ceramic scintillator material and investigate different doping amounts to elucidate its bright luminescence enabled by quantum cutting. We demonstrate that the host CsPbCl3 perovskite structure is maintained up to 7% mole Yb3+, which produces a light yield of 102,000 photons/MeV. We show that these polycrystalline perovskite scintillators can be pressed into a ceramic pellet and used for x-ray imaging with a resolution of approximately 0.1 mm. The combination of high light yield and the simple, inexpensive synthesis reported in this work demonstrates the great potential of Yb3+:CsPbCl3 for scintillation applications.
Recent grants
Frequent coauthors
- 28 shared
Benjamin J. Foley
University of Virginia
- 19 shared
Alexander Z. Chen
- 19 shared
Seunghun Lee
- 18 shared
Tobias Hanrath
Cornell University
- 18 shared
Lucy U. Yoon
University of Virginia
- 16 shared
Craig M. Brown
NIST Center for Neutron Research
- 16 shared
Tianran Chen
- 15 shared
Matthew R. Alpert
Charlottesville Medical Research
Labs
Education
Other, Chemical Engineering
Cooper Union
Ph.D., Applied Physics
Cornell University
Other, Chemistry
Columbia University
Awards & honors
- NASA Early Career Faculty Award (2015)
- VSGC New Investigator Award 2015
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