Seong-Hun Lee

Asymmetric Control of DC-Link Voltages for Separate MPPTs in Three-Level Inverters

It is important to improve the overall efficiency of a photovoltaic (PV) inverter when it is connected to the grid. Fundamentally, the conversion efficiency from dc to ac power of an inverter is important. However, in the presence of partial shading, maximum power point tracking (MPPT) on PV modules is more important than the conversion efficiency. In this paper, a new control method for a three-level inverter is proposed. With the proposed method, each dc-link voltage of the three-level inverter can be asymmetrically regulated. When PV modules are split into two and each split module is connected to the respective dc-link capacitors of the inverter, the asymmetric control can be helpful because separate MPPTs are possible. The effectiveness of the proposed method was examined through experiments with a T-type three-level inverter, where each dc-link capacitor was supplied by a PV simulator emulating two separate PV modules under different shading conditions.

38.4: Full‐Color Patterning of Quantum Dot (QD) Light‐Emitting Diodes using QD Transplanting Techniques

We provide simple and versatile QD transplanting method, which allows well-defined QD patterns down to a few micrometers and also provides compatibility with conventional device fabrication process and device architecture. We also demonstrate red, green, and blue QLEDs with transplanted QD active layers and characterize them in systematic correlation study between QD pattern morphology and device performances.

Redox-active ionic liquid electrolyte with multi energy storage mechanism for high energy density supercapacitor

A bimodal redox-active ionic liquid electrolyte for supercapacitors with high energy density was demonstrated. The suggested bimodal electrolyte, which consists of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) and 1-ethyl-3-methylimidazolium halide (EMI-X, X = Br, I) as a redox active couple, shows the three types of energy storage mechanism: a classical EDL capacitance; a pseudo-capacitance from the redox reaction of halide species, such as bromide and iodide; and an EDL capacitance strongly enhanced by ion size effects. When EMITFSI is mixed with small ions, the thickness of the ionic layer becomes thinner and even more ions are packed into the electrode due to the decrement of excluded-volume effects and the increment of electrostatic interactions. The supercapacitor containing a mixture of EMITFSI and EMI-I showed a considerably high performance with 175.6 W h kg−1 and 4994.5 W kg−1 at 1 A g−1 and excellent cycling stability up to 5000 cycles.