• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.363.1-363.1
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• 2016

Transparent and stretchable conductors are expected to be an essential component in future stretchable optoelectronic devices. Until now, two main methods have been commonly employed to fabricate transparent and stretchable conductors by using metal nanomaterials: creating buckling configurations and creating network configurations. In this report, a novel strategy for obtaining transparent and stretchable conductors is presented, one that employs these two main approaches simultaneously. To the best of our knowledge, this proposed configuration of a buckled long nanofiber network in this study has not yet been reported. In order to provide the transparent conductors with dual mode stretchability originating from simultaneous buckled and network configurations, a buckled Au@polyvinylpyrrolidone (PVP) nanofiber network (hereafter referred to BANN for convenience) was fabricated by transferring Au-metallized electrospun PVP nanofibers onto a prestrained polydimethylsiloxane (PDMS) substrate. Our BANN shows considerably lower strain sensitivity of resistance than that of straight Au@PVP nanofiber network. Durability tests conducted by performing cyclic tensile strain reveal that the relative change in resistance of BANN (prestrain = 20%) is quite small after 1000 cycles. We also demonstrate that this BANN exhibits superior performance over widely used indium tin oxide conductors with regard to high optical transmittance and low sheet resistance.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.87.2-87.2
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• 2015

Transparent conductors are commonly used in photoelectric devices, where the electric energy converts to light energy or vice versa. Energy consumption devices, such as LEDs, Displays, Lighting devices use the electrical energy to generate light by carrier recombination. Meanwhile, solar cell is the only device to generate electric energy from the incident photon. Most photoelectric devices require a transparent electrode to pass the light in or out from a device. Beyond the passive role, transparent conductors can be employed to form Schottky junction or heterojunction to establish a rectifying current flow. Transparent conductor-embedded heterojunction device provides significant advantages of transparent electrode formation, no need for intentional doping process, and enhanced light-reactive surface area. Herein, we present versatile applications of transparent conductors, such as NiO, ZnO, ITO in photoelectric devices of solar cells and photodetectors for high-performing UV or IR detection. Moreover, we also introduce the growth of transparent ITO nanowires by sputtering methods for large scale application.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.444.2-444.2
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• 2014

Transparent conductors (TCs) are typically applied as an ohmic contact layer for photoelectric devices. Recent researches have illuminated a unique rectifying-junction design between a transparent conductor and a semiconductor layer. This approach may lead a significant reduction of device-fabrication steps and cost. A high-performing heterojunction device is presented, which provided significant photoelectric responses. This covers the fabrication processes, rectifying-junction formations and device analyses.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.387.1-387.1
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• 2016

Transparent materials are necessary for most photoelectric devices, which allow the light generation from electric energy or vice versa. Metal oxides are usual materials for transparent conductors to have high optical transmittance with good electrical properties. Functional designs may apply in various applications, including solar cells, photodetectors, and transparent heaters. Nanoscale structures are effective to drive the incident light into light-absorbing semiconductor layer to improve solar cell performances. Recently, the new metal oxide materials have inaugurated functional device applications. Nickel oxide (NiO) is the strong p-type metal oxide and has been applied for all transparent metal oxide photodetector by combining with n-type ZnO. The abrupt p-NiO/n-ZnO heterojunction device has a high transmittance of 90% for visible light but absorbs almost entire UV wavelength light to show the record fastest photoresponse time of 24 ms. For other applications, NiO has been applied for solar cells and transparent heaters to induce the enhanced performances due to its optical and electrical benefits. We discuss the high possibility of metal oxides for current and future transparent electronic applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.4
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• pp.241-246
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• 2016

ZnO thin films have wide application areas due to its versatile properties as transparent conductors, wide-bandgap n-type semiconductors, gas sensor materials, and etc. We have performed a systematic investigation on ultraviolet-assisted CVD (chemical vapor deposition) method. Ultraviolet irradiation during the deposition of ZnO causes chemical reduction on the growing surface; which results in the reduction of the deposition rate, increase in the surface roughness, and decrease of the electrical resistivity. These effects produce larger characteristic variation with various deposition conditions in terms of surface morphology and optical/electrical properties compared to normal CVD deposited ZnO thin films. This versatile controllability of ultraviolet-assisted CVD can provide a larger processing options in the fabrication of nano-structured materials and flexible device applications.

• Current Applied Physics
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• v.18 no.12
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• pp.1583-1591
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• 2018

We analysed perovskite $CH_3NH_3PbI_{3-x}Cl_x$ inverted planer structure solar cell with nickel oxide (NiO) and spiroMeOTAD as hole conductors. This structure is free from electron transport layer. The thickness is optimized for NiO and spiro-MeOTAD hole conducting materials and the devices do not exhibit any significant variation for both hole transport materials. The back metal contact work function is varied for NiO hole conductor and observed that Ni and Co metals may be suitable back contacts for efficient carrier dynamics. The solar photovoltaic response showed a linear decrease in efficiency with increasing temperature. The electron affinity and band gap of transparent conducting oxide and NiO layers are varied to understand their impact on conduction and valence band offsets. A range of suitable band gap and electron affinity values are found essential for efficient device performance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.537-546
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• 2023

Intrinsically stretchable light-emitting diodes, composed of stretchable electrodes, charge transport layers, and luminescent materials, have garnered significant interest for enhancing human well-being and advancing the field of deformable electronics. Various luminescent materials, such as perovskites and organics, have been integrated with stretchable elastomers to function as the stretchable emissive layers in these intrinsically stretchable LEDs. Stretchable conductors including Ag nanowire based percolating structures and conducting polymers have been utilized as stretchable transparent electrode. Despite this progress, their performances in terms of efficiency and stability remain challenging compared to their structurally stretchable and rigid LED counterparts. This review offers a comprehensive overview of recent advancements in intrinsically stretchable LEDs, focusing on material innovations.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.174-177
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• 1991

Fluorine-doped $SnO_2\;(SnO_2:F)$ films were prepared in ordinary atmosphere on borosilicate glass substrates using pyrosol deposition method starting from the solutions composed of $SnCl_4-5H_2O-NH_4F-CH_3OH-H_2O-HCl$ in an attempt to develop transparent conductors for use in amorphous silicon (a-Si) solar cello. The deposition rate of films increased with the increase in the content of $H_2O$, whereas it decreased with increasing the content of $CH_3OH$. When air was used as the carrier gas, the lowest electrical resistivity was obtained from a solution having $CH_3OH/H_2O$ mol ratio of about $2{\sim}3$ in the solution. The use of $N_2$ of the same flow rate as the carrier gab resulted always in the high resistive films, but the resistivity of the films decreased continuously with the increase in the content of $H_2O$. The surface morphology and preferred orientation of films were also affected by the solvent composition and the content of HCl in the solution. The room-temperature resistance of the films were fairly stable after heat-treatments up to $600^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.5
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• pp.517-521
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• 2012

Carbon nanotubes (CNTs) have been regarded as a promising material for the fabrication of flexible conductors such as transparent electrodes, flexible heaters, and transparent speakers. In this study, a multiwalled carbon nanotube (MWCNT) film was deposited on a polyethylene terephthalate (PET) substrate using a spraying technique. MWCNTs were dispersed in water using sodium dodecyl sulfate (SDS). To evaluate the effect of the weight ratio between SDS and MWCNTs on the electromechanical properties of the film, direct tensile tests and optical strain measurement were conducted. It was found that the CNT film hardly affected the mechanical behavior of CNT/PET composite films, while the electrical behavior of the CNT film was strongly affected by the SDS concentration in the CNT film. The electrical resistance of CNT/PET films gradually increased with the strain applied to the PET substrate, even up to a large strain that ruptured the substrate.

• Korean Journal of Materials Research
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• v.15 no.8
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• pp.518-520
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• 2005

Effects of the $O_2/Ar$ flow ratio in the sputtering process on the crystallinity, surface roughness, carrier concentration, carrier mobility, and optical properties of Al-doped ZnO thin films deposited on sapphire (001) substrates by RF magnetron sputtering were investigated. XRD spectra showed a preferred orientation along the c-axis and a minimum FWHM of the (002) XRD intensity peak for the $O_2/Ar$ flow ratio of 0.5. The (101)peak also appeared and the degree of preferred orientation decreased as the $O_2/Ar$ flow ratio increased from 0.5 to 1.0. AFM analysis results showed that the surface roughness was lowest at the $O_2/Ar$ flow ratio of 0.5 and tended to increase owing to the increase of the grain size as the $O_2/Ar$ flow ratio increased further. According to the Hall measurement results the carrier concentration and carrier mobility of the fan decreased and thus the resistivity increased as the $O_2/Ar$ flow ratio increased. The transmittance of the ZnO:Al film deposited on the glass substrate was characteristic of a standing wave. The transmittance increased as the $O_2/Ar$ flow ratio in-RF magnetron sputtering increased up to 0.5. Considering the effects of the $O_2/Ar$ flow ratio on the surface roughness, electrical resistivity and transmittance properties of the ZnO:Al film the optimum $O_2/Ar$ flow ratio was 0.5 in the RF magnetron sputter deposition of the ZnO:Al film.