A5074072858- Organic Electronics and Photovoltaics
- Conducting polymers and applications
- Organic Light-Emitting Diodes Research
- Perovskite Materials and Applications
- Molecular Junctions and Nanostructures
- Semiconductor materials and devices
- Luminescence and Fluorescent Materials
- Quantum Dots Synthesis And Properties
- Strong Light-Matter Interactions
- Plasmonic and Surface Plasmon Research
- Photochemistry and Electron Transfer Studies
- Nanowire Synthesis and Applications
- Semiconductor Quantum Structures and Devices
- Silicon Nanostructures and Photoluminescence
- Thin-Film Transistor Technologies
- Chalcogenide Semiconductor Thin Films
- Thermal Radiation and Cooling Technologies
- Crystallization and Solubility Studies
- X-ray Diffraction in Crystallography
- Recycling and Waste Management Techniques
- Electronic and Structural Properties of Oxides
- Semiconductor materials and interfaces
- Radical Photochemical Reactions
- Photoreceptor and optogenetics research
- Crystallography and molecular interactions
University of Minnesota
2016-2025
University of Minnesota System
2016-2024
Twin Cities Orthopedics
2020-2022
Minneapolis Institute of Arts
2016-2020
University of Missouri
2020
Development Agency of Serbia
2012-2018
Princeton University
2002-2006
University of Manitoba
2004
University of Southern California
2004
Aeronix (United States)
2003
We demonstrate efficient blue electrophosphorescence using exothermic energy transfer from a host consisting of N,N′-dicarbazolyl-3,5-benzene (mCP) to the phosphorescent iridium complex iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic). By examining temperature dependence radiative lifetime and photoluminescence film mCP doped with FIrpic, we confirm existence in contrast endothermic characteristic N,N′-dicarbazolyl-4-4′-biphenyl FIrpic system. In employing between...
We demonstrate efficient, deep-blue organic electrophosphorescence using a charge-trapping phosphorescent guest, iridium(III) bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6) doped in the wide-energy-gap hosts, diphenyldi(o-tolyl)silane (UGH1) and p-bis(triphenylsilyly)benzene (UGH2), where exciton formation occurs directly on guest molecules. Charge trapping is confirmed by dependence of drive voltage electroluminescence spectrum concentration. Ultraviolet photoemission...
Two approaches are reported to achieve efficient blue near-UV emission from triscyclometalated iridium(III) materials related the previously complex, fac-Ir(ppz)3 (ppz = 1-phenylpyrazolyl-N,C2'). The first involves replacement of phenyl group ppz ligand with a 9,9-dimethyl-2-fluorenyl group, i.e., fac-tris(1-[(9,9-dimethyl-2-fluorenyl)]pyrazolyl-N,C2')iridium(III), abbreviated as fac-Ir(flz)3. Crystallographic analysis reveals that both fac-Ir(flz)3 and have similar coordination environment...
An organic electrophosphorescent white‐light‐emitting device (see Figure) containing green, red, and blue emitters doped into a 9 nm thick wide‐bandgap material is shown to attain maximum forward viewing power efficiency of (26±3) lm W –1 . The high attributed the efficient confinement excitons charge within emissive layer, thin highly dopant.
Four ultrahigh energy gap organosilicon compounds [diphenyldi(o-tolyl)silane (UGH1), p-bis(triphenylsilyl)benzene (UGH2), m-bis(triphenylsilyl)benzene (UGH3), and 9,9'-spirobisilaanthracene (UGH4)] were employed as host materials in the emissive layer of electrophosphorescent organic light-emitting diodes (OLEDs). The high singlet (∼4.5 eV) triplet (∼3.5 energies associated with these effectively suppress both electron transfer quenching pathways between dopant material, leading to deep blue...
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...
White stacked electrophosphorescent organic light-emitting devices employing three metallorganic phosphors in a compound emission layer (see Figure) are demonstrated. They show an external efficiency of 51 % and power 20.7 lm W–1 at practical illumination intensities. A transparent MoO3 film between two adjacent elements efficiently injects charge into the elements.
We demonstrate highly efficient electroluminescence from silicon nanocrystals (SiNCs). In an optimized nanocrystal-organic light-emitting device, peak external quantum efficiencies of up to 8.6% can be realized with emission originating solely the SiNCs. The high reported here for first time that appropriate choice device architecture it is possible achieve indirect band gap semiconductor.
A simple technique employing reverse bias measurements of photoluminescent efficiency is described to determine the excitonic singlet-triplet formation statistics electroluminescent organic thin films. Using this method, singlet fractions in films two emissive materials commonly used light emitting devices, tris(8-hydroxyquinoline) aluminum $({\mathrm{Alq}}_{3})$ and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), are found be $(20\ifmmode\pm\else\textpm\fi{}1)%$...
We examine the effects of nonradiative losses on lasing in crystalline and amorphous organic thin films. In films, dominant loss mechanism is singlet-singlet annihilation, this must be avoided if to achieved at practical current densities. The electrically pumped crystalline-tetracene laser structure Sch\"on et al. [Science 289, 599 (2000)] studied detail. Optical electrical confinement bulk appears unable explain spectral narrowing reported; consequently, we consider electron-hole plasmas,...
We demonstrate saturated, deep blue organic electrophosphorescence using the facial- and meridianal- isomers of fluorine-free emitter tris(phenyl-methyl-benzimidazolyl)iridium(III)(f-Ir(pmb)3 m-Ir(pmb)3, respectively) doped into wide energy gap host, p-bis(triphenylsilyly)benzene (UGH2). The highest electrophosphorescent transition occurs at a wavelength λ=389nm for fac- isomer λ=395nm mer- isomer. emission chromaticity is characterized by Commission Internationale de l’Eclairage coordinates...
We demonstrate enhanced power conversion efficiency in organic photovoltaic (OPV) cells incorporated into a plasmonic nanocavity array. The array is formed between patterned Ag anode and an unpatterned Al cathode. This structure leads to the confinement of optical energy absorption OPV. Devices characterized under simulated solar illumination show 3.2-fold increase compared OPVs with anodes. observed enhancement also reflected external quantum efficiency, spectral response consistent...
Abstract This work demonstrates an approach for measuring the Förster radius of energy transfer between electron donating and accepting materials commonly used in organic photovoltaic cells (OPVs). While processes are surprisingly common OPVs, they often incorrectly ignored measurements exciton diffusion length models device performance. Here, efficiency emissive donor absorptive acceptor is investigated through complementary experimental theoretical techniques. accomplished by spatially...
We demonstrate hybrid inorganic-organic light-emitting devices with peak electroluminescence (EL) at a wavelength of 868 nm using silicon nanocrystals (SiNCs). An external quantum efficiency 0.6% is realized in the forward-emitted direction, emission originating primarily from SiNCs. Microscopic characterization indicates that complete coverage SiNCs on conjugated polymer hole-transporting layer required to observe efficient EL.
Abstract The electrical and structural behavior of uniformly mixed films boron subphthalocyanine chloride (SubPc) C 60 their performance in organic photovoltaic cells is explored. Device shows a strong dependence on active‐layer donor–acceptor composition, peak efficiency realized at 80 wt.% . origin this ‐rich optimum composition elucidated terms morphological changes the active layer upon diluting SubPc with While neat found to be amorphous, containing show clear nanocrystalline domains...
Previous studies have identified triplet‐triplet annihilation and triplet‐polaron quenching as the exciton density‐dependent mechanisms which give rise to efficiency roll‐off observed in phosphorescent organic light‐emitting devices (OLEDs). In this work, these processes are independently probed, impact of recombination zone width on severity various OLED architectures is examined directly. It found that employing a graded‐emissive layer (G‐EML) architecture due both quenching, while employ...
We demonstrate strong exciton-photon coupling in an optical microcavity containing a thermally evaporated polycrystalline organic thin film. Microcavity polaritons result from between the 0-0 excitonic transition of 3,4,7,8 napthalenetetracarboxylic dianhydride and cavity photon. For thicker films, 0-1 also couples to mode, as vibronic relaxation is overcome by short Rabi period for coupling. To our knowledge, this first report photon multiple transitions single material, made possible...
Bathocuproine (BCP) or tris(acetylacetonato)ruthenium(III) (Ru(acac)3) is used as the exciton-blocking layer (EBL) in photovoltaic cells. The difference thickness-dependent efficiency characteristics between blockers (see Figure) that Ru(acac)3 energy-level alignment allows for transport of holes from cathode to C60 acceptor level, whereas BCP relies on metal-deposition-induced damage charge transport.
We demonstrate enhanced exciton diffusion in an organic photovoltaic cell through the incorporation of a phosphorescent sensitizer. The increase length (LD) is realized using composite electron donor layer consisting N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPD) host doped with guest fac-tris(2-phenylpyridine) iridium [Ir(ppy)3]. presence phosphor at low concentration allows for population long-lived NPD triplet state and LD. An LD from 6.5±0.3 to 11.8±0.6 nm extracted...
Graded donor-acceptor heterojunctions for efficient organic photovoltaic cells are fabricated using boron subphthalocyanine chloride (SubPc) and C60. The graded heterojunction significantly increases the exciton diffusion efficiency relative to a planar architecture, improves charge collection uniformly mixed architecture. A power conversion of (4.2 ± 0.1)% is realized in OPV at 100 mW cm−2 AM1.5G illumination intensity.
Abstract An experimental approach to determine the spatial extent and location of exciton recombination zone in an organic light‐emitting device (OLED) is demonstrated. This technique applicable a wide variety OLED structures used examine OLEDs which have double‐ (D‐EML), mixed‐ (M‐EML), or graded‐emissive layer (G‐EML) architecture. The important design parameter, as local optical field sensed by greatly determines efficiency angular distribution far‐field light extraction. parameter that...
Electronic structure calculations of five crystallography-imitated structures CsMI3 perovskites with M = Ge, Sn, Pb, Mg, Ca, Sr, and Ba were performed. The formation energy different perovskite phases, their relative stability, structural electronic properties explored. sensitivity the to choice density functional was investigated, predictions compared experimental results. outcome this study is that Mg are unlikely form in cubic, tetragonal, or orthorhombic phases because they have positive...