arXiv subjects

Chang-Ki Moon

Publications and source records attributed to Chang-Ki Moon.

5 recordsLinked to original sources

arXiv2026

Round-Robin Test of a Light-Emitting Electrochemical Cell: Establishing a Reference Protocol for Quality Research

Emerging technologies benefit from a jointly established reference protocol, which can lower the bar of entry for new researchers while serving as a calibration standard for established actors. The light-emitting electrochemical cell (LEC) combines electrochemistry and optoelectronics in an intricate manner, and it can by that enable sustainable and commercially relevant printing fabrication of emissive thin-film devices. However, LEC performance is sensitive to a range of material and processing parameters, which frequently results in inadequate, or even erroneous, device evaluation. With this in mind, we present herein a LEC reference protocol, which details the sourcing of materials and the procedures and parameters for robust device fabrication and operation. The protocol has been tested across nine international research groups, and the collected results from this interlaboratory round-robin test confirm that good LEC performance can be reproducibly obtained following our protocol. We also identify common pitfalls that can arise during LEC development, and present practical steps for attaining optimum LEC performance. We hope this reference protocol will improve the quality of future LEC research and serve as a guide for future researchers entering this vibrant field.

cond-mat.soft↗

arXiv2025

Tunable photogating in a molecular aggregate coupled graphene phototransistor

We present a graphene photodetector coupled to a layer of aggregated organic semiconductor. A graphene phototransistor is covered with a thin film of merocyanine molecules. The aggregation of the molecular layer can be controlled by the deposition parameters and post-deposition annealing to obtain films ranging from amorphous to a highly aggregated state. The molecular layer has a uniaxial structure with excitonic transitions whose transition dipole moments are well defined. The presence of the molecular layer results in an enormous increase in the response of the phototransistor. We further demonstrate that the signal-enhancement is due to p-photodoping of the graphene. The spectroscopic photoresponse suggests that the photodoping via monomers and molecular aggregates takes place differently. Our photodetector is a platform to study the influence of molecular aggregation and order on charge transport processes between aggregated organic semiconductors and two-dimensional materials.

cond-mat.mes-hall↗

arXiv2025

Electrochemically induced hyperfluorescence based on the formation of charge-transfer excimers

Used extensively in sensing applications, the application of solution-state electrochemiluminescent devices (ECLDs) in lighting and displays has been constrained by their low luminance and short operational lifetime. Here, we report a record improvement in the luminance, efficiency, and operational longevity of ECLDs by introducing electrochemically induced hyperfluorescence (ECiHF) and demonstrate its use in a calligraphic display. We use the double-decker arrangement assumed by the electron donor and acceptor segments of the molecule TpAT-tFFO to realize thermally activated delayed fluorescence from an electrogenerated charge-transfer (CT) excimer state and a subsequent energy transfer to the rubrene emitter TBRb. ECLDs based on this strategy achieve an unprecedented luminance of >6,200 cd/m2 and their operational lifetime is more than 10-fold longer than all previous ECLDs with meaningful efficiency or brightness. We identify energy level alignment between excimer and emitter as a crucial factor for efficient ECiHF; spectroelectrochemical analysis reveals that devices with energy gaps < 0.4 eV operate on a pure excimer mechanism across a wide range of frequencies. Our findings highlight the potential of ECiHF for improving ECLDs and pave the way to commercial applications of this form of fluid light.

physics.optics↗

arXiv2024

High-power pulsed electrochemiluminescence for optogenetic manipulation of Drosophila larval behaviour

Electrochemiluminescence (ECL) produces light through electrochemical reactions and has shown promise for various analytic applications in biomedicine. However, the use of ECL devices (ECLDs) as light sources has been limited due to insufficient light output and low operational stability. In this study, we present a high-power pulsed operation strategy for ECLDs to address these limitations and demonstrate their effectiveness in optogenetic manipulation. By applying a biphasic voltage sequence with short opposing phases, we achieve intense and efficient ECL through an exciplex-formation reaction pathway. This approach results in an exceptionally high optical power density, exceeding 100 microW/mm2, for several thousand pulses. Balancing the ion concentration by optimizing the voltage waveform further improves device stability. By incorporating multiple optimized pulses into a burst signal separated by short rest periods, extended light pulses of high brightness and with minimal power loss over time were obtained. These strategies were leveraged to elicit a robust optogenetic response in fruit fly (Drosophila melanogaster) larvae expressing the optogenetic effector CsChrimson. The semi-transparent nature of ECLDs facilitates simultaneous imaging of larval behaviour from underneath, through the device. These findings highlight the potential of ECLDs as versatile optical tools in biomedical and neurophotonics research.

physics.optics↗

arXiv2017

Unraveling the orientation of phosphors doped in organic semiconducting layers

Emitting dipole orientation (EDO) is an important issue of emitting materials in organic light-emitting diodes (OLEDs) for an increase of outcoupling efficiency of light. The origin of preferred orientation of emitting dipole of spherically shaped iridium-based heteroleptic phosphorescent dyes doped in organic layers is revealed by simulation of vacuum deposition using molecular dynamics (MD) along with quantum mechanical (QM) characterization of the phosphors for a direct comparison with experimental observations of EDO. Consideration of both the electronic transitions in a molecular frame and the orientation of the molecules interacting with the environment at the vacuum/molecular film interface allows quantitative analyses of the EDO depending on host molecules and dopant structures. Interaction between the phosphor and nearest host molecules on the surface, minimizing the non-bonding energy determines the molecular alignment during the vacuum deposition. Parallel alignment of the main cyclometalating ligands in the molecular complex due to host interactions rather than the ancillary ligand orienting to vacuum leads to the horizontal EDO.

cond-mat.mtrl-sci↗