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장찬욱,황성원,Seung Hyun Shin,Suk-Ho Choi 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.7
Despite several reports on perovskite resistive random access memories (RRAMs), most of them are based on transparent conductive oxide electrodes, not suitable for high exibility. We first employ multilayer-graphene (MLG) transparent conductive electrodes (TCEs) for exible hybrid organic-inorganic perovskite RRAMs, showing reversible bipolar resistive switching behaviors with about 0.68 and 0:5 V as set and reset bias voltages, respectively. The low-resistance state (LRS) and high-resistance state (HRS) of the RRAMs are almost constant even by data retention, switching, and bending for > 104 s, > 500 cycles, and > 1000 cycles, respectively. The I-V curve at the HRS during the set process is consistent with the Ohm's law for small voltages, but is well described by the space-charge-limited conduction mechanism for large voltages. The Ohmic conduction is also observed at the LRS during the set process. These behaviors are similarly repeated during the reset process, and well explained based on defect migration and charge trapping. These results suggest that perovskite RRAMs can be remarkably stable enough for practical applications by employing MLG TCEs.
In-situ Monitoring of AuCl3-doping and -dedoping Behaviors in Graphene
신동희,김성,장찬욱,김종민,김주환,최석호 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.9
In-situ variations of the surface morphology, transmittance, sheet resistance, and Dirac curveof graphene have been monitored during AuCl3-doping and annealing-induced-dedoping processes. The transmittance of graphene shows a monotonically-decreasing behavior due to doping and subsequentannealing at higher temperatures (TA), resulting from the continuing increase in the surfacecorrugations due to intensified coalescing of Au clusters. Electronic parameters, such as the sheetresistance, work function, Dirac point, and electron mobility, show their extreme values when annealedat 50 C after doping, which can be attributed to further enhancement of a reaction donatingelectrons to Cl ions from graphene at TA = 50 C. The annealing at higher TA induces a dedopingeffect due to the Cl desorption, thereby decreasing the doping efficiency. These results suggest thatCl anions play a crucial role in the doping and the dedoping processes, especially causing variationsin the electronic properties of graphene.
김종민,서상우,신동희,이하승,김주환,장찬욱,김성,최석호 한국물리학회 2017 Current Applied Physics Vol.17 No.8
Graphene/silver nanowires (Ag NWs)-doped graphene stacks are employed for Si Schottky-junction solar cells as transparent conductive electrodes (TCEs). The doping of graphene by Ag NWs decreases the series resistance of the solar cells and enhances the electrical conductivity of the graphene TCEs, resulting in remarkable improvements of the diode properties of the solar cells. In addition, the Ag NWs on the graphene reduces the reflectance of the solar cells as well as the transmittance of the graphene TCEs. This trade-off correlation makes the power-conversion efficiency maximized to 3.51% at concentration of Ag NWs (nA) ¼ 0.1 wt%. The long-term stabilities of the photovoltaic properties are greatly improved by the encapsulation of the Ag NWs/graphene TCEs with another graphene because of the excellence of graphene as a gas-barrier. These and other nA-dependent behaviors of Raman spectra, work function, sheet resistance, external quantum efficiency, and DC conductivity/optical conductivity ratio are discussed to explain the photovoltaic properties of the solar cells.