Research Institute for Solar and Sustainable Energies

Gwangju, South Korea

Research Institute for Solar and Sustainable Energies

Gwangju, South Korea

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Jo G.,Princeton University | Hong W.-K.,Korea Basic Science Institute | Choe M.,Gwangju Institute of Science and Technology | Park W.,Gwangju Institute of Science and Technology | And 2 more authors.
IEEE Transactions on Nanotechnology | Year: 2012

We report an efficient method to predictably control the conductance and operation voltage of ZnO nanowire field-effect transistors (FETs) with bilayer polyimide (PI)-SiO$ 2 gate dielectric by selectively generating oxide-trapped charges via proton beam irradiation. The bilayer gate dielectrics was made by polyimide and thermally grown SiO$ 2 , which prevents negatively charged interface states between the gate dielectric and the ZnO nanowire after proton irradiation. The proton beam-induced charges trapped in the SiO$ 2 dielectric layer can effectively enhance the electric field toward the n-channel ZnO nanowire, which allows for more accumulation of electrons in the conduction channel of the ZnO nanowire. As a result, the conductance increased and the threshold voltages shifted toward the negative gate bias direction after irradiation. Furthermore, selective modulation of the electrostatic characteristics of the ZnO nanowire FETs was possible by varying the proton irradiation time, which is important for practical application of these devices. © 2002-2012 IEEE.


Kim J.,Research Institute for Solar and Sustainable Energies | Kim H.,Research Institute for Solar and Sustainable Energies | Kim G.,Gwangju Institute of Science and Technology | Back H.,Gwangju Institute of Science and Technology | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2014

We report a new method for developing a low-temperature solution processed vanadium oxide (s-VOx) and poly(4-styrene sulfonic acid) (PSS) composite to act as an efficient hole-transport layer (HTL) in polymer solar cells (PSCs). By compositing the s-VOx and PSS (s-VO x:PSS), the work function values of the s-VOx:PSS changed from 5.0 to 5.3 eV. Therefore, the energy level barrier between the HTL and organic active layer decreased, facilitating charge injection/extraction at the interfaces. In addition, the s-VOx:PSS films were denser and had more pin-hole-free surfaces than pristine s-VOx films, resulting in enhanced PSC performance due to significantly decreased leakage currents and excellent device stability in ambient condition. Because our approach of combining soluble transition metal oxide (TMO) and polymeric acid shows dramatically better performance than pristine TMO, we expect that it can provide useful guidelines for the synthesis and application of TMOs for organic electronics in the future. © 2013 American Chemical Society.


Min J.-H.,Gwangju Institute of Science and Technology | Min J.-H.,Research Institute for Solar and Sustainable Energies | Jang S.-Y.,Gwangju Institute of Science and Technology | Jang S.-Y.,Research Institute for Solar and Sustainable Energies | And 8 more authors.
RSC Advances | Year: 2015

We have designed and fabricated Ag-mesh-combined graphene current spreading layers (CSLs) for GaN-based near-ultraviolet light-emitting diodes (NUV LEDs). Three different types of the CSLs were fabricated having 300 μm, 150 μm, and 75 μm gaps between the mesh lines. Optical and electrical properties were investigated and the performance of the LEDs having the CSLs and were compared with those of LEDs having indium tin oxide and graphene CSLs. The light output power of the LEDs with the Ag-mesh-combined graphene CSL adopting 150 μm-gap was highest at both the same current injection and at the same input power. This was possible due to the lowering of the sheet resistance via the adoption of an Ag mesh and the networking of the Ag mesh using a graphene sheet with very little transmittance loss. © 2015 The Royal Society of Chemistry.


Min J.-H.,Gwangju Institute of Science and Technology | Min J.-H.,Research Institute for Solar and Sustainable Energies | Seo T.H.,Korea Institute of Science and Technology | Choi S.-B.,Gwangju Institute of Science and Technology | And 12 more authors.
Current Applied Physics | Year: 2016

We have demonstrated the effect of p-GaN hole concentration on a graphene current spreading layer (CSL) for stabilization and improved performance of a near-ultraviolet light-emitting diode (NUV LED). While NUV LEDs with a more lightly-doped p-GaN showed poor electrical and optical properties and unstable performance, NUV LEDs with more heavily-doped p-GaN (∼2 × 1017 cm−3) showed very stable, outstanding performance. The main factor of the improvement was the enhanced contact property between the graphene CSLs and the p-GaN that resulted from the increase of the hole concentration, which led to a thinner barrier and an enhanced current injection. From our results, we were able to determine that hole concentration as heavy as 2 × 1017 cm−3 in p-GaN layers is a primary condition in NUV LEDs with graphene-based CSLs. © 2016 Elsevier B.V.

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