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Jun, Sungwoo,Choi, Kwang Wook,Kim, Kwang-Seok,Kim, Dae Up,Lee, Chan-Jae,Han, Chul Jong,Lee, Cheul-Ro,Ju, Byeong-Kwon,Kim, Jong-Woong Elsevier Applied Science Publishers 2019 Composites science and technology Vol.182 No.-
<P><B>Abstract</B></P> <P>Conventional photodetectors (PDs) are based on measuring photocurrent, which is formed by the separation of electron-hole pairs generated in semiconductors upon light irradiation, through electrodes in direct contact with the semiconductors. Such devices are usually fabricated through complicated and precise processes such as thin film formation by vacuum deposition and fine patterning by photolithography and etching. In addition, PDs have a drawback that the contact quality between the electrode and the semiconductor is easily affected by external stress applied to the device. These issues make it difficult to implement a mechanically flexible device driven by conventional sensing mechanisms. Here we report a simple structured PD based on a semiconductor particle-polymer composite layer surrounded by two facing transparent electrodes, inspired by the fact that the dielectric properties of certain semiconductors change upon light irradiation with a photonic energy greater than or equal to their bandgap. In order to realize this, we synthesized a transparent and stretchable polymer, polyurethane-urea (PUU), which is compatible with Ag nanowires (AgNWs) and polydimethylsiloxane (PDMS) used for implementing stretchable electrodes, and dispersed ZnS:Cu particles into the PUU to form a sensory layer. The fabricated composite surrounded by two facing AgNW-based transparent electrodes was transparent and stretchable, and the capacitance formed at the composite sensitively changed upon irradiation of light with a wavelength of 420 nm and a power of 1.2 mW/cm<SUP>2</SUP> even when the device was stretched or cut in half.</P>
Jun, Sungwoo,Choi, Su Bin,Han, Chul Jong,Yu, Yeon-Tae,Lee, Cheul-Ro,Ju, Byeong-Kwon,Kim, Jong-Woong American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.4
<P>Most photodetectors developed to date essentially measure photocurrents induced by the generation and separation of electron-hole pairs in semiconductors during irradiation. Although the above light detection method is well established, highly sensitive, and applicable to a broad range of semiconductor materials, it requires the presence of a stable and direct contact between the semiconductor and the electrode for accurate photocurrent measurements. In turn, this prerequisite necessitates the use of various costly processes for device fabrication (e.g., photolithography and vacuum deposition of semiconductors/metals) and complicates the development of flexible devices. Herein, inspired by the fact that the dielectric properties of certain materials can be changed by light irradiation, we dispersed ZnS/Cu semiconducting particles in poly(vinyl butyral) to prepare a free-standing composite film and formed two layers of Ag nanowire electrodes on both sides of the cured composite to fabricate a photodetector of a completely new type. The developed device exhibited a capacitance very sensitive to irradiation with light of a specific wavelength and additionally featured the advantages of simple structure/operation mechanism, mechanical flexibility, and transparency, not showing any signs of performance deterioration even after severe damage.</P> [FIG OMISSION]</BR>
Jun, Sungwoo,Kim, Youngmin,Ju, Byeong-Kwon,Kim, Jong-Woong Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.429 No.-
<P><B>Abstract</B></P> <P>A multifunctional alternate current electroluminescent device (ACEL) was achieved by compositing ZnS:Cu particles in polyvinyl butyral (PVB) with two layers of percolated silver nanowire (AgNW) electrodes. The strong hydrogen bonding interactions and entanglement of PVB chains considerably strengthened the PVB, and thus, the cured mixture of ZnS:Cu particles and freestanding PVB required no additional support. The device was fabricated by embedding AgNWs on both sides of the ZnS:Cu-PVB composite film using an inverted layer process and intense-pulsed-light treatment. The strong affinity of PVB to the polyvinyl pyrrolidone (PVP) layer, which capped the AgNWs, mechanically stabilized the device to such an extent that it could resist 10,000 bending cycles under a curvature radius of 500μm. Using AgNW networks in both the top and bottom electrodes made a double-sided light-emitting device that could be applied to wearable lightings or flexible digital signage. The capacitance formed in the device sensitively varied with the applied bending and unfolding, thus demonstrating that the device can also be used as a deformation sensor.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A self-supporting alternate current electroluminescent device (ACEL) was fabricated. </LI> <LI> A polyvinyl butyral was first synthesized and cross-linked with ZnS:Cu particles. </LI> <LI> Silver nanowire networks were directly embedded on both sides as electrodes. </LI> <LI> The ACEL devices were mechanically reliable during 10,000 bending cycles. </LI> <LI> The ACEL devices could be used as thin, wearable light-emitting deformation sensors. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Jun, Sungwoo,Kim, Sun Ok,Lee, Hee-Jin,Han, Chul Jong,Lee, Chan-Jae,Yu, Yeon-Tae,Lee, Cheul-Ro,Ju, Byeong-Kwon,Kim, Youngmin,Kim, Jong-Woong The Royal Society of Chemistry 2019 Journal of materials chemistry. A, Materials for e Vol.7 No.7
<P>Most intrinsically healable polymers feature a soft nature and high flowability that arise from the reversible formation of bonds (<I>e.g.</I>, cross-linkages). Unfortunately, a trade-off relationship between mechanical strength and healing capability is observed for the majority of these polymers, which necessitates the search for better alternatives. Herein, we synthesized a urethane acrylate-based intrinsically healable material with enhanced mechanical properties, demonstrating that this enhancement originates from the presence of UV curing-produced dynamic urea bonds acting as reversible cross-linkages. The synthesized polymer was hybridized with silver nanowires (AgNWs) to afford a transparent pressure-sensitive e-skin capable of irradiation-induced healing, <I>i.e.</I>, the heating of AgNWs by a series of intense pulsed light (IPL) irradiations allowed one to instantly and rapidly repair the cutting marks or scratches artificially formed on e-skin sensors. The healing ability was originated from the enhanced flowability and thermal expansion of the polymer during IPL irradiation. Consecutive cutting-healing cycling showed that the cutting marks formed at the same locations could be effectively repaired for up to five times. The fringing effect-associated capacitance of a AgNW tandem compound pattern significantly increased with increasing pressure applied to the sensor surface, and the electric function of damaged sensors was successfully restored by irradiation-induced healing.</P>
Sungwoo Jun,Hagyoul Bae,Hyeongjung Kim,Jungmin Lee,Sung-Jin Choi,Dae Hwan Kim,Dong Myong Kim IEEE 2015 IEEE electron device letters Vol.36 No.2
<P>We report a dual-sweep combinational transconductance technique for separate extraction of parasitic source (R<SUB>S</SUB>) and drain (R<SUB>D</SUB>) resistances in thin-film transistors (TFTs) by combining forward and reverse transfer characteristics. In the proposed technique, gate bias-dependent total resistance [R<SUB>TOT</SUB> (V<SUB>GS</SUB>)] and degradation of the transconductance due to the parasitic resistance at the source terminal during the dual-sweep characterization are employed. Applying the proposed technique to amorphous oxide semiconductor TFTs with various combinations of channel length (L) and width (W), we successfully separated R<SUB>S</SUB> and R<SUB>D</SUB>. A model for the W- and L-dependences of the extracted parasitic resistances is also provided.</P>
Sungwoo Jun,Chunhyung Jo,Hagyoul Bae,Hyunjun Choi,Dae Hwan Kim,Dong Myong Kim IEEE 2013 IEEE electron device letters Vol.34 No.5
<P>We report a unified subthreshold coupling factor technique for a simultaneous extraction of the surface potential (ψ<SUB>S</SUB>) and the subgap density-of-states [DOS: g(E)] over the bandgap in amorphous semiconductor thin film transistors (TFTs). It is fully based on the experimental gate bias-dependent coupling factor [m(V<SUB>GS</SUB>)] under subthreshold bias. Through the proposed technique only with current-voltage data under subthreshold operation, a unified extraction of the DOS with a consistent mapping of the gate bias (V<SUB>GS</SUB>) to the subgap energy is obtained. Applying to amorphous InGaZnO TFTs, g(E) is obtained to be a superposition of two exponential functions with N<SUB>TA</SUB> = 1.62 × 10<SUP>17</SUP> eV<SUP>-1</SUP> cm<SUP>-3</SUP> and kT<SUB>TA</SUB> = 0.026 eV for the tail states while N<SUB>DA</SUB> = 6.5 × 10<SUP>16</SUP> eV<SUP>-1</SUP> cm<SUP>-3</SUP> and kT<SUB>DA</SUB> = 0.22 eV for the deep states.</P>
Kim, Sungwoo,Kang, Meejae,Kim, Seajin,Heo, Jin-Hyuk,Noh, Jun Hong,Im, Sang Hyuk,Seok, Sang Il,Kim, Sang-Wook American Chemical Society 2013 ACS NANO Vol.7 No.6
<P>We report the first synthesis of colloidal CuInTe<SUB>2</SUB>, CuInTe<SUB>2–<I>x</I></SUB>Se<SUB><I>x</I></SUB> gradient alloyed quantum dots (QDs) through a simple hot injection method. We confirmed the composition of synthesized QDs to cationic rich phase of CuIn<SUB>1.5</SUB>Te<SUB>2.5</SUB> and Cu<SUB>0.23</SUB>In<SUB>0.36</SUB>Te<SUB>0.19</SUB>Se<SUB>0.22</SUB> with XPS and ICP analysis, and we have also found that the gradient alloyed Cu<SUB>0.23</SUB>In<SUB>0.36</SUB>Te<SUB>0.19</SUB>Se<SUB>0.22</SUB> QDs exhibit greatly improved stability over the CuIn<SUB>1.5</SUB>Te<SUB>2.5</SUB> QDs. The solution-processed solar cell based on the gradient alloyed Cu<SUB>0.23</SUB>In<SUB>0.36</SUB>Te<SUB>0.19</SUB>Se<SUB>0.22</SUB> QDs exhibited 17.4 mA/cm<SUP>2</SUP> of short circuit current density (<I>J</I><SUB>sc</SUB>), 0.40 V of open circuit voltage (<I>V</I><SUB>oc</SUB>), 44.1% of fill factor (FF), and 3.1% of overall power conversion efficiency at 100 mW/cm<SUP>2</SUP> AM 1.5G illumination.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-6/nn401274e/production/images/medium/nn-2013-01274e_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn401274e'>ACS Electronic Supporting Info</A></P>