arXiv subjects

Jongwon Lee

Publications and source records attributed to Jongwon Lee.

22 records · Page 2Linked to original sources

arXiv2021

Multiple Exciton Generation Solar Cells: Numerical Approach of Quantum Yield Extraction and its Limiting Efficiencies

Multiple exciton generation solar cells exhibit a low power conversion efficiency owing to nonradiative recombination even if numerous electron and hole pairs are generated per incident photon. This paper elucidates the non-idealities of multiple exciton generation solar cells (MEGSCs) and alternative approaches for realizing photovoltaic (PV) devices similar to MEGSCs. First, we present mathematical approaches for determining the quantum yield (QY) to discuss the non-idealities of MEGSCs by adjusting the delta function. In particular, we employ the Gaussian distribution function to present the occupancy status of carriers at each energy state by Dirac delta function. By adjusting the Gaussian distribution function for each energy state, we obtain the ideal and non-ideal QYs. Through this approach, we discuss the material imperfections of MEGSCs by analyzing the mathematically obtained QYs. By calculating the ratio between the radiative and nonradiative recombination, we can discuss the status of radiative recombination calculate Furthermore, we apply this approach into the detailed balance limit of MEGSC to investigate the practical limit of MEGSC.

physics.app-ph↗

arXiv2019

Experimental and Theoretical Realization of Zenneck Wave-based Non-Radiative, Non-Coupled Wireless Power Transmission

A decade ago, non-radiative wireless power transmission re-emerged as a promising alternative to deliver electrical power to devices where a physical wiring proved to be unfeasible. However, existing approaches are neither scalable nor efficient when multiple devices are involved, as they are restricted by factors like coupling and external environments. Zenneck waves are excited at interfaces, like surface plasmons and have the potential to deliver electrical power to devices placed on a conducting surface. Here, we demonstrate, efficient and long range delivery of electrical power by exciting nonradiative waves over metal surfaces to multiple loads. Our modeling and simulation using Maxwells equation with proper boundary conditions shows Zenneck type behavior for the excited waves and are in excellent agreement with experimental results. In conclusion, we physically realize a radically different power transfer system, based on a wave, whose existence has been fiercely debated for over a century.

physics.app-ph↗

arXiv2015

Gradient Nonlinear Pancharatnam-Berry Metasurfaces

We apply the Pancharatnam-Berry phase approach to plasmonic metasurfaces loaded by highly nonlinear multi-quantum well substrates, establishing a platform to control the nonlinear wavefront at will based on giant localized nonlinear effects. We apply this approach to design flat nonlinear metasurfaces for efficient second-harmonic radiation, including beam steering, focusing, and polarization manipulation. Our findings open a new direction for nonlinear optics, in which phase matching issues are relaxed, and an unprecedented level of local wavefront control is achieved over thin devices with giant nonlinear responses.

physics.optics↗

arXiv2015

Experimental Demonstration of Phase Modulation and Motion Sensing Using Graphene-Integrated Metasurfaces

Plasmonic metasurfaces are able to modify the wavefront by altering the light intensity, phase and polarization state. Active plasmonic metasurfaces would allow dynamic modulation of the wavefront which give rise to interesting application such as beam-steering, holograms and tunable waveplates. Graphene is an interesting material with dynamic property which can be controlled by electrical gating at an ultra-fast speed. We use a graphene-integrated metasurface to induce a tunable phase change to the wavefront. The metasurface supports a Fano resonance which produces high-quality resonances around 7.7 microns. The phase change is measured using a Michleson interferometry setup. It is shown that the reflection phase can change up to 55 degrees. In particular the phase can change by 28 degrees while the amplitude is nearly constant. The anisotropic optical response of the metasurface is used to modulate the ellipticity of the reflected wave in response to an incident field at 45 degree. We show a proof of concept application of our system in potentially ultra-fast laser interferometry with sub-micron accuracy.

physics.optics↗