A5061466865- Organic Electronics and Photovoltaics
- Conducting polymers and applications
- Organic Light-Emitting Diodes Research
- Perovskite Materials and Applications
- Thin-Film Transistor Technologies
- Molecular Junctions and Nanostructures
- Luminescence and Fluorescent Materials
- Silicon and Solar Cell Technologies
- solar cell performance optimization
- Optical properties and cooling technologies in crystalline materials
- Semiconductor Quantum Structures and Devices
- Photochemistry and Electron Transfer Studies
- Integrated Circuits and Semiconductor Failure Analysis
- Advancements in Photolithography Techniques
- Random lasers and scattering media
- Semiconductor Lasers and Optical Devices
- Color Science and Applications
- Advanced Optical Imaging Technologies
- Photoreceptor and optogenetics research
- Optical Coatings and Gratings
- Photonic Crystals and Applications
- Electron and X-Ray Spectroscopy Techniques
- Photonic and Optical Devices
- Liquid Crystal Research Advancements
- Impact of Light on Environment and Health
Minnesota Department of Transportation
2022
University of Cambridge
2016-2019
Minneapolis Institute of Arts
2016
University of Minnesota
2012-2016
University of Minnesota System
2016
Twin Cities Orthopedics
2016
Exciton generation, migration, and dissociation are key processes that play a central role in the design operation of many organic optoelectronic devices. In photovoltaic cells, charge generation often occurs only at an interface, forcing exciton to migrate from point photogeneration order be dissociated into its constituent carriers. Consequently, performance these devices is strongly impacted by typically short distance over which excitons able move. The ability engineer materials or...
Easily processed materials with the ability to transport excitons over length scales of more than 100 nanometers are highly desirable for a range light-harvesting and optoelectronic devices. We describe preparation organic semiconducting nanofibers comprising crystalline poly(di-n-hexylfluorene) core solvated, segmented corona consisting polyethylene glycol in center polythiophene at ends. These exhibit exciton transfer from lower-energy coronas end blocks, which occurs direction interchain...
Donor-acceptor organic solar cells often show low open-circuit voltages (V OC) relative to their optical energy gap (E g) that limit power conversion efficiencies ~12%. This loss is partly attributed the offset between E g and of intermolecular charge transfer (CT) states at donor-acceptor interface. Here we study generation occurring in PIPCP:PC61BM, a system with very driving for initial separation g-E CT ~ 50 meV) high internal quantum efficiency (η IQE 80%). We track strength electric...
Rapid, long-range charge separation in polymer-fullerene organic solar cells (OSCs) enables electrons and holes to move beyond their Coulomb capture radius overcome geminate recombination. Understanding the nature of generation recombination mechanisms efficient, nonfullerene-acceptor-based OSCs are critical further improve device performance. Here we report dynamics an OSC using a perylene diimide (PDI) dimer acceptor. We use transient absorption spectroscopy track time evolution...
Abstract Efficient vacuum‐processed organic light‐emitting diodes are fabricated using a carbene–metal–amide material, CMA1. An electroluminescence (EL) external quantum efficiency of 23% is achieved in host‐free emissive layer comprising pure Furthermore efficiencies up to 26.9% host–guest layers. EL spectra found depend on both the emissive‐layer doping concentration and choice host enabling tuning emission color from mid‐green (Commission Internationale de l'Éclairage co‐ordinates [0.24,...
Electrically injected charge carriers in organic light-emitting devices (OLEDs) undergo recombination events to form singlet and triplet states a 1:3 ratio, representing fundamental hurdle for achieving high quantum efficiency. Dopants based on thermally activated delayed fluorescence (TADF) have emerged as promising candidates addressing the spin statistics issue OLEDs. In these materials, reverse singlet-triplet intersystem crossing (rISC) becomes efficient, thereby activating luminescence...
Abstract Efficient conjugated polymer optoelectronic devices benefit from concomitantly high luminescence and charge carrier mobility. This is difficult to achieve, as interchain interactions, which are needed ensure efficient transport, tend also reduce radiative recombination lead solid-state quenching effects. Many studies detail strategies for reducing these interactions increase luminescence, or modifying chain packing motifs improve percolation transport; however achieving properties...
Donor–acceptor organic solar cells often show high quantum yields for charge collection, but relatively low open-circuit voltages (VOC) limit power conversion efficiencies to around 12%. We report here the behavior of a system, PIPCP:PC61BM, that exhibits very electronic disorder (Urbach energy less than 27 meV), carrier mobilities in blend (field-effect mobility holes >10–2 cm2 V–1 s–1), and driving initial separation (50 meV). These characteristics should give excellent performance,...
Cesium lead halide nanocrystals, CsPbX3 (X = Cl, Br, I), exhibit photoluminescence quantum efficiencies approaching 100% without the core–shell structures usually used in conventional semiconductor nanocrystals. These high make these crystals ideal candidates for light-emitting diodes (LEDs). However, because of large surface area to volume ratio, halogen exchange between perovskite nanocrystals different compositions occurs rapidly, which is one limiting factors white-light applications...
Organic semiconductors characterized by a small singlet–triplet exciton energy splitting exhibit efficient reverse intersystem crossing and thermally activated delayed fluorescence. Consequently, transport may occur along both the singlet triplet excited states, each with unique photophysical behavior transfer mechanisms. Delayed fluorescence systems, therefore, provide test bed for characterizing role of spin in diffusion. Concentration- temperature-dependent characterization combined...
Broadband photodetection is achieved by integrating three electron donor materials with complementary absorption into an organic photodetector (OPD). While a single donor-acceptor heterojunction can show broadband response, the spectral tunability intrinsically limited to profiles of active materials. Here, we demonstrate OPDs consisting multiple bulk heterojunctions arranged in tandem. These high responsivity under moderate reverse bias from ultraviolet near-infrared. By combining tandem...
In planar heterojunction organic photovoltaic devices (OPVs), broad spectral coverage can be realized by incorporating multiple molecular absorbers in an energy-cascade architecture. Here, this approach is combined with a host–guest donor layer architecture previously shown to optimize exciton transport for the fluorescent semiconductor boron subphthalocyanine chloride (SubPc) when diluted optically transparent host. order maximize absorption efficiency, OPVs that utilize both photoactive...
Using temperature-dependent optical-control spectroscopy, we show that the binding energy of localised charge-transfer state is about 90 meV in a range organic photovoltaic systems.
Exciton transport in organic semiconductors is a critical, mediating process many optoelectronic devices. Often, the diffusive and subdiffusive nature of excitons these systems can limit device performance, motivating development strategies to direct exciton transport. In this work, directed achieved with incorporation permeable interfaces. These interfaces introduce symmetry-breaking imbalance energy transfer, leading motion. Despite their obvious utility for enhanced harvesting...
Temperature dependent measurements of the exciton diffusion length (<italic>L</italic><sub>D</sub>) are performed for three archetypical small-molecule, organic semiconductors: aluminum tris-(8-hydroxyquinoline) (Alq<sub>3</sub>), dicyanovinyl-terthiophene (DCV3T), and boron subphthalocyanine chloride (SubPc).
Optoelectronic devices based on conjugated polymers often rely multilayer device architectures, as it is difficult to design all the different functional requirements, in particular need for efficient luminescence and fast carrier transport, into a single polymer. Here we study photophysics of recently discovered class with high charge mobility low degree energetic disorder investigate whether possible this system achieve by molecular photoluminescence quantum yield without sacrificing...
The addition of spacing layers in organic photovoltaic cells (OPVs) can enhance light absorption by optimizing the spatial distribution incident optical field multilayer structure. We explore effect OPVs achieved using a diluted electron acceptor layer C60. While is often realized buffer thickness, we find that via dilution leads to with similar or enhanced photocurrent. This observed despite smaller quantity absorbing molecules, suggesting more efficient use absorbed photons. In fact, found...
The synthesis, characterization and solar cell performance of PCDTBT its highly soluble analogue hexyl-PCDTBT with cross-conjugated benzoyl moieties at the carbazole comonomer are presented. Through use both model reactions time-controlled microwave-assisted Suzuki polycondensation, base-induced cleavage group from polymer backbone has been successfully suppressed. Compared to commonly used symmetrically branched alkyl motif, substituent lowers energy levels as well band gap, consequently...
We show that the optical design of strong‐cavity, top‐emitting (SCTE) OLEDs is limited by tradeoffs between efficiency and color‐shift. Color correction technologies can be leveraged to overcome these tradeoffs, opening space for SCTE OLEDs.