Jeongno Lee

An effective energy harvesting method from a natural water motion active transducer

We demonstrated a new water motion active transducer (WMAT) without any external bias-voltage sources or additional processes, which critically limit the use of conventional passive capacitive transducers that convert mechanical motion into electric energy. From a simple structure, we successfully turned on an LED using various kinds of natural water motion. The WMAT, which has wide applicability, has good potential to be a candidate for generating sustainable electric energy.

Increased shell thickness in indium phosphide multishell quantum dots leading to efficiency and stability enhancement in light-emitting diodes

We report efficient indium phosphide (InP) quantum dot-based light-emitting diodes (QD-LEDs). The current efficiency and the device stability of QD-LEDs were enhanced by increasing the thickness of ZnS outer shell of InP/ZnSe/ZnS multishell QDs. Reversible luminance degradation was observed in operation of QD-LEDs, which was hypothesized to result from QD charging. QDs having thicker ZnS shell with strong confinement suppressed the luminescence quenching as well as QD charging. Our findings about the reversible QD charging and the developed performance by the thick ZnS outer shell would help to rationalize the luminance quenching issue in QD-LED operation.

Inverted InP quantum dot light-emitting diodes using low-temperature solution-processed metal–oxide as an electron transport layer

The present work shows the inverted InP quantum dot light-emitting diodes (QD-LEDs) with inorganic metal oxide layers. In the inverted structure of ITO/ZnO/InP QDs/CBP/MoO3/Al, a sol?gel derived ZnO film was used as an electron transport layer (ETL) and MoO3 was used as a hole injection layer (HIL). In contrary to high annealing temperature (>200 ?C) for conventional ZnO films, low temperature annealing (?150 ?C) was performed for sol?gel derived ZnO film. The performance of the inverted QD-LEDs was efficiently improved by optimization of the annealing time and temperature of ZnO ETL. The current efficiency was significantly improved about 215% by lowering annealing temperature of ZnO ETL.

Study of ethanolamine surface treatment on the metal-oxide electron transport layer in inverted InP quantum dot light-emitting diodes

The present work shows the effect of ethanolamine surface treatment on inverted InP quantum dot light-emitting diodes (QD-LEDs) with inorganic metal oxide layers. In the inverted structure of ITO/ZnO/InP QDs/CBP/MoO3/Al, a sol-gel derived ZnO film was used as an electron transport layer (ETL) and MoO3 was used as a hole injection layer (HIL). First, ethanolamine was treated as a surface modifier on top of the ZnO electron transport layer. The optical performance of the QD-LED device was improved by the ethanolamine surface treatment. Second, low temperature annealing (<200°C) was performed on the ZnO sol-gel electron transport layer, followed by an investigation of the effect of the ZnO annealing temperature. The efficiency of the inverted QD-LEDs was significantly enhanced (more than 3-fold) by optimization of the ZnO annealing temperature.

Electrical aging effect of ZnS based quantum dots for white light-emitting diodes

The present work reports cadmium-free colloidal ZnS:Al quantum dot (QD) based white quantum dot light-emitting diodes (QD-LEDs). The device was fabricated with a structure of ITO/PEDOT:PSS/PVK/QDs/TPBi/LiF/Al using synthesized ZnS:Al QDs which has 393 nm of peak wavelength and sub peaks in visible wavelength. White emission with high color rending index (CRI) was achieved by the combination of blue emission from PVK and ZnS:Al QDs, electroplex emission at the interface between PVK and ZnS:Al QDs, and Al traps/defects emission, which are controlled by electrical aging effect. The characteristic of our device shows the potential for spectrum tunable and Cd-free white QD-LEDs in the near future.