About

John Asbury is a Professor of Chemistry and the Associate Department Head for Graduate Education at the Eberly College of Science. His research group specializes in ultrafast spectroscopy, particularly the development and application of two-dimensional infrared (2D IR) spectroscopy to study chemical processes in functional organic electronic materials. His work combines ultrafast infrared spectroscopy with electrochemical techniques to elucidate the structure and dynamics of charged defects and their roles in electron transfer, charge carrier diffusion, and bimolecular charge recombination in emerging photovoltaic materials. Professor Asbury's research aims to understand how molecular structures of defects in organic electronic materials influence their charge transport, trapping, and recombination characteristics. He employs vibrational spectra to examine charged defects, using 2D IR spectroelectrochemistry to map structural features directly onto vibrational signatures. His work is interdisciplinary, involving collaborations across engineering and chemistry, and focuses on materials such as polymeric blends and colloidal quantum dots used in organic photovoltaics. His contributions advance the understanding of defect control in organic electronics, which is crucial for improving the efficiency of devices like solar cells, lighting, and displays.

Research topics

• Photochemistry
• Chemistry
• Materials science
• Organic chemistry
• Physics
• Chemical physics
• Quantum mechanics
• Nanotechnology
• Optoelectronics
• Atomic physics
• Composite material
• Crystallography
• Stereochemistry

Selected publications

• Dynamic Nanocrystal-Ligand Boundaries: Reversible Photoinduced Ligand Detachment from Quantum Dots in Solution

  Journal of the American Chemical Society · 2026-01-15

  articleOpen accessSenior author

  The porosity of ligand shells of colloidal quantum dots (QDs) can influence the overall rate and yield of charge transfer processes occurring at their surfaces. However, the density of ligand shells on QDs can also influence their colloidal and photochemical stability. We used time-resolved infrared spectroscopy to show that photoinduced ligand detachment, the tendency for certain ligands to detach from QD surfaces when the nanocrystals are promoted to their excitonic excited states, can be used to transiently enhance the porosity of oleic acid-passivated CdSe QDs in solution. Furthermore, we synthesized CdSe QDs with varying ligand shell densities to examine the corresponding influence that van der Waals interactions among ligands have on the yield of photoinduced ligand detachment and the time scale on which ligands return to QD surfaces. We observed that oleic acid ligands on CdSe QDs with lower shell densities have a higher probability of escape for longer periods of time. Despite this, oleic acid ligands on fully passivated CdSe QDs are still able to photodetach, resulting in a transient increase of their ligand shell porosity. In contrast, QDs with multilayer ligand coronas exhibit negligible photoinduced ligand detachment because the outer molecular layers introduce a type of cage effect, preventing the escape of the interior ligands. Our findings suggest the intriguing possibility that photoinduced ligand detachment can be used to transiently decrease the density of ligand shells of QDs to facilitate charge transfer processes while still allowing them to be fully passivated between excitation events for photochemical and colloidal stability.

  PublisherDOI

• Understanding and Controlling V-Doping and S-Vacancy Behavior in Two-Dimensional Semiconductors- Toward Predictive Design

  ArXiv.org · 2025-06-26

  preprintOpen accessSenior author

  Doping in transition metal dichalcogenide (TMD) monolayers provides a powerful method to precisely tailor their electronic, optical, and catalytic properties for advanced technological applications, including optoelectronics, catalysis, and quantum technologies. However, doping efficiency and outcomes in these materials are strongly influenced by the complex interactions between introduced dopants and intrinsic defects, particularly sulfur vacancies. This coupling between dopants and defects can lead to distinctly different behaviors depending on doping concentration, presenting significant challenges in the predictable and controlled design of TMD properties. For example, in this work we systematically varied the p-type vanadium (V) doping density in tungsten disulfide (WS2) monolayers and observed a transition in doping behavior. At low concentrations, V-dopants enhance the native optical properties of WS2, as evidenced by increased photoluminescence, without introducing new electronic states. However, at higher concentrations, V-dopants promote the formation of vanadium-sulfur vacancy complexes that generate mid-gap states, with energies that can be precisely tuned by controlling the vanadium concentration. Using a combination of excitation- and temperature-dependent photoluminescence microscopy, atomic-resolution scanning transmission electron microscopy, and first-principles calculations, we identify attractive interactions between p-type V-dopants and n-type monosulfur vacancies. Our results provide mechanistic understanding of how enthalpic dopant-defect interactions versus entropic effects govern the balance between property enhancement versus perturbation of transition metal dichalcogenides and suggest a pathway toward the rational design of doping strategies for next-generation optoelectronic, catalytic, and quantum devices.

  PublisherOA PDFDOI

• Understanding and Controlling Vanadium Doping and Sulfur Vacancy Behavior in Two-Dimensional Semiconductors: Toward Predictive Design

  ACS Nano · 2025-09-19 · 3 citations

  articleSenior authorCorresponding

  Doping in transition-metal dichalcogenide (TMD) monolayers provides a powerful method to precisely tailor their electronic, optical, and catalytic properties for advanced technological applications, including optoelectronics, catalysis, and quantum technologies. However, the doping efficiency and outcomes in these materials are strongly influenced by the complex interactions between introduced dopants and intrinsic defects, particularly sulfur vacancies. This coupling between dopants and defects can lead to distinctly different behaviors depending on the doping concentration, presenting significant challenges in the predictable and controlled design of TMD properties. For example, in this work we systematically varied the p-type vanadium(V) doping density in tungsten disulfide (WS2) monolayers and observed a transition in doping behavior. At low concentrations, V-dopants enhance the native optical properties of WS2, as evidenced by increased photoluminescence, without introducing new electronic states. However, at higher concentrations, V-dopants promote the formation of vanadium–sulfur vacancy complexes that generate midgap states, with energies that can be precisely tuned by controlling the vanadium concentration. Using a combination of excitation- and temperature-dependent photoluminescence microscopy, atomic-resolution scanning transmission electron microscopy, and first-principles calculations, we identify attractive interactions between p-type V-dopants and n-type monosulfur vacancies. Our results provide a mechanistic understanding of how enthalpic dopant–defect interactions versus entropic effects govern the balance between property enhancement and perturbation of TMDs and suggest a pathway toward the rational design of doping strategies for next-generation optoelectronic, catalytic, and quantum devices.

  PublisherDOI

• Reversible Ligand Detachment from CdSe Quantum Dots Following Photoexcitation

  The Journal of Physical Chemistry Letters · 2024-04-04 · 14 citations

  articleSenior authorCorresponding

  The nanocrystal-ligand boundaries of colloidal quantum dots (QDs) mediate charge and energy transfer processes that underpin photochemical and photocatalytic transformations at their surfaces. We used time-resolved infrared spectroscopy combined with transient electronic spectroscopy to probe vibrational modes of the carboxylate anchoring groups of stearate ligands attached to cadmium selenide (CdSe) QDs that were optically excited in solid nanocrystal films. The vibrational frequencies of surface-bonded carboxylate groups revealed their interactions with surface-localized holes in the excited states of the QDs. We also observed transient and reversible photoinduced ligand detachment from CdSe nanocrystals within their excited state lifetime. By probing both surface charge distributions and ligand dynamics on QDs in their excited states, we open a pathway to explore how the nanocrystal-ligand boundary can be understood and controlled for the design of QD architectures that most effectively drive charge transfer processes in solar energy harvesting and photoredox catalysis applications.

  PublisherDOI

• Influence of Rhenium Concentration on Charge Doping and Defect Formation in MoS₂

  Advanced Electronic Materials · 2024-07-05 · 14 citations

  articleOpen accessCorresponding

  Abstract Substitutionally doped transition metal dichalcogenides (TMDs) are essential for advancing TMD‐based field effect transistors, sensors, and quantum photonic devices. However, the impact of local dopant concentrations and dopant–dopant interactions on charge doping and defect formation within TMDs remains underexplored. Here, a breakthrough understanding of the influence of rhenium (Re) concentration is presented on charge doping and defect formation in MoS 2 monolayers grown by metal–organic chemical vapor deposition (MOCVD). It is shown that Re‐MoS 2 films exhibit reduced sulfur‐site defects, consistent with prior reports. However, as the Re concentration approaches ⪆2 atom%, significant clustering of Re in the MoS 2 is observed. Ab Initio calculations indicate that the transition from isolated Re atoms to Re clusters increases the ionization energy of Re dopants, thereby reducing Re‐doping efficacy. Using photoluminescence (PL) spectroscopy, it is shown that Re dopant clustering creates defect states that trap photogenerated excitons within the MoS 2 lattice, resulting in broad sub‐gap emission. These results provide critical insights into how the local concentration of metal dopants influences carrier density, defect formation, and exciton recombination in TMDs, offering a novel framework for designing future TMD‐based devices with improved electronic and photonic properties.

  PublisherOA PDFDOI

• Influence of Substrate-Induced Charge Doping on Defect-Related Excitonic Emission in Monolayer MoS₂

  The Journal of Physical Chemistry Letters · 2024-07-25 · 10 citations

  articleSenior authorCorresponding

  Many applications of transition metal dichalcogenides (TMDs) involve transfer to functional substrates that can strongly impact their optical and electronic properties. We investigate the impact that substrate interactions have on free carrier densities and defect-related excitonic (XD) emission from MoS2 monolayers grown by metal–organic chemical vapor deposition. C-plane sapphire substrates mimic common hydroxyl-terminated substrates. We demonstrate that transferring MoS2 monolayers to pristine c-plane sapphire dramatically increases the free electron density within MoS2 layers, quenches XD emission, and accelerates exciton recombination at the optical band edge. In contrast, transferring MoS2 monolayers onto inert hexagonal boron nitride (h-BN) has no measurable influence on these properties. Our findings demonstrate the promise of utilizing substrate engineering to control charge doping interactions and to quench broad XD background emission features that can influence the purity of single photon emitters in TMDs being developed for quantum photonic applications.

  PublisherDOI

• Tuning polymer-backbone coplanarity and conformational order to achieve high-performance printed all-polymer solar cells

  Nature Communications · 2024-03-09 · 54 citations

  articleOpen access

  All-polymer solar cells (all-PSCs) offer improved morphological and mechanical stability compared with those containing small-molecule-acceptors (SMAs). They can be processed with a broader range of conditions, making them desirable for printing techniques. In this study, we report a high-performance polymer acceptor design based on bithiazole linker (PY-BTz) that are on par with SMAs. We demonstrate that bithiazole induces a more coplanar and ordered conformation compared to bithiophene due to the synergistic effect of non-covalent backbone planarization and reduced steric encumbrances. As a result, PY-BTz shows a significantly higher efficiency of 16.4% in comparison to the polymer acceptors based on commonly used thiophene-based linkers (i.e., PY-2T, 9.8%). Detailed analyses reveal that this improvement is associated with enhanced conjugation along the backbone and closer interchain π-stacking, resulting in higher charge mobilities, suppressed charge recombination, and reduced energetic disorder. Remarkably, an efficiency of 14.7% is realized for all-PSCs that are solution-sheared in ambient conditions, which is among the highest for devices prepared under conditions relevant to scalable printing techniques. This work uncovers a strategy for promoting backbone conjugation and planarization in emerging polymer acceptors that can lead to superior all-PSCs.

  PublisherOA PDFDOI

• (Invited) Influence of Y6 Aggregation on Energetics and Charge Generation in High Performance OPV Blends

  ECS Meeting Abstracts · 2024-08-09

  article1st authorCorresponding

  We investigated the origin of the high ratio of open circuit voltage to charge transfer state energy (eV OC /E CT ) of OPV polymer blends consisting of the electron donating polymer PM6 and the non-fullerene electron acceptor Y6. PM6-Y6 and related donor-acceptor OPV blends exhibit remarkable optoelectronic properties and record power conversion efficiencies in part because of their unusually high eV OC /E CT ratios, which is believed to be related to the small energetic offset of the HOMO levels of PM6 and Y6. In this study, we varied the amount of Y6 in PM6 blends as a means to control the aggregation of Y6 molecules. We examined the corresponding influence that Y6 aggregation has on the energetic offsets and the charge generation efficiency of the materials by probing the appearance of polaron absorption signals in the mid-infrared using time-resolved infrared spectroscopy. Furthermore, we examined the optical absorption and emission spectra of the PM6-Y6 blends over the range of compositions to correlate the efficiency of charge generation with the signatures of Y6 aggregation in the optical spectra. We observed an abrupt transition around 30 mass% Y6 content at which polarons were efficiently generated by charge separation from PM6 to Y6. Comparison to composition dependent GIWAXS studies of PM6-Y6 blends revealed the formation of Y6 aggregates around the same 30 mass% threshold. These observations demonstrate that aggregation of Y6 molecules is required for charge separation to occur from PM6 to Y6 as measured through the mid-infrared absorption of polarons in the TRIR spectra. Although charges were efficiently generated in blends with only 30 mass% Y6 content, OPV device studies revealed that 50-60 mass% Y6 was needed to reach optimized short-circuit current and OPV device efficiency because these measurements convolve charge generation with charge transport. These findings clarify the optoelectronic properties of the novel class of Y6 acceptors and emphasize the importance of molecular aggregation for tuning the energetics of high performance systems that minimize energy offsets for maximum OPV power conversion efficiencies.

  PublisherDOI

• Thermal Disorder‐Induced Strain and Carrier Localization Activate Reverse Halide Segregation

  Advanced Materials · 2023-12-07 · 6 citations

  articleOpen accessCorresponding

  Abstract The reversal of halide ions is studied under various conditions. However, the underlying mechanism of heat‐induced reversal remains unclear. This work finds that dynamic disorder‐induced localization of self‐trapped polarons and thermal disorder‐induced strain (TDIS) can be co‐acting drivers of reverse segregation. Localization of polarons results in an order of magnitude decrease in excess carrier density (polaron population), causing a reduced impact of the light‐induced strain (LIS – responsible for segregation) on the perovskite framework. Meanwhile, exposing the lattice to TDIS exceeding the LIS can eliminate the photoexcitation‐induced strain gradient, as thermal fluctuations of the lattice can mask the LIS strain. Under continuous 0.1 W cm⁻ 2 illumination (upon segregation), the strain disorder is estimated to be 0.14%, while at 80 °C under dark conditions, the strain is 0.23%. However, in situ heating of the segregated film to 80 °C under continuous illumination (upon reversal) increases the total strain disorder to 0.25%, where TDIS is likely to have a dominant contribution. Therefore, the contribution of entropy to the system's free energy is likely to dominate, respectively. Various temperature‐dependent in situ measurements and simulations further support the results. These findings highlight the importance of strain homogenization for designing stable perovskites under real‐world operating conditions.

  PublisherOA PDFDOI

• Dilute Rhenium Doping and its Impact on Intrinsic Defects in MoS2

  arXiv (Cornell University) · 2023-01-31 · 2 citations

  preprintOpen access

  Substitutionally-doped 2D transition metal dichalcogenides are primed for next-generation device applications such as field effect transistors (FET), sensors, and optoelectronic circuits. In this work, we demonstrate substitutional Rhenium (Re) doping of MoS2 monolayers with controllable concentrations down to 500 parts-per-million (ppm) by metal-organic chemical vapor deposition (MOCVD). Surprisingly, we discover that even trace amounts of Re lead to a reduction in sulfur site defect density by 5-10x. Ab initio models indicate the free-energy of sulfur-vacancy formation is increased along the MoS2 growth-front when Re is introduced, resulting in an improved stoichiometry. Remarkably, defect photoluminescence (PL) commonly seen in as-grown MOCVD MoS2 is suppressed by 6x at 0.05 atomic percent (at.%) Re and completely quenched with 1 at.% Re. Furthermore, Re-MoS2 transistors exhibit up to 8x higher drain current and enhanced mobility compared to undoped MoS2 because of the improved material quality. This work provides important insights on how dopants affect 2D semiconductor growth dynamics, which can lead to improved crystal quality and device performance.

  PublisherOA PDFDOI

Recent grants

• Infrared Electro-Optical Spectroscopy of Degradation Pathways in Organo-Halide Perovskite Photovoltaics

  NSF · $395k · 2015–2019

• Temperature Jump Infrared Electrochemical Spectroscopy (TIR-SEC) of Catalytic Intermediates

  NSF · $432k · 2020–2025

• CAREER: Elucidating Structures of Charge Traps in Organic Photovoltaic Materials Using Ultrafast 2D IR Spectroelectrochemistry

  NSF · $624k · 2009–2015

Frequent coauthors

• Tianquan Lian

  Emory University

  47 shared

• Christopher Grieco

  Auburn University

  43 shared

• Ryan D. Pensack

  Micron (United States)

  30 shared

• Kyle T. Munson

  Pennsylvania State University

  30 shared

• Grayson S. Doucette

  Pennsylvania State University

  29 shared

• Eric R. Kennehan

  28 shared

• Hirendra N. Ghosh

  National Institute of Science Education and Research

  23 shared

• M. D. Fayer

  Stanford University

  21 shared

Labs

• Asbury GroupPI

Education

• Postdoctoral Scholar, Chemistry

  Stanford University

  2005

• PhD, Chemistry

  Emory University

  2001

• BS, Chemistry

  University of Tennessee

  1996

Awards & honors

• DOE CAREER Award (2012)
• NSF CAREER Award (2009)
• 3M Non-Tenured Faculty Grant (2008, 2009)
• Eli Lilly Analytical Chemistry New Faculty Award (2007)
• Camille and Henry Dreyfus New Faculty Award (2005)