• Title/Summary/Keyword: photovoltaic devices

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Self-Assembly of Pentacene Molecules on Epitaxial Graphene

  • Jung, Woo-Sung;Lee, Jun-Hae;Ahn, Sung-Joon;Park, Chong-Yun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.230-230
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    • 2012
  • Graphene have showed promising performance as electrodes of organic devices such as organic transistors, light-emitting diodes, and photovoltaic solar cells. In particular, among various organic materials of graphene-based organic devices, pentacene has been regarded as one of the promising organic material because of its high mobility, chemical stability. In the bottom-contact device configuration generally used as graphene based pentacene devices, the morphology of the organic semiconductors at the interface between a channel and electrode is crucial to efficient charge transport from the electrode to the channel. For the high quality morphology, understanding of initial stages of pentacene growth is essential. In this study, we investigate self-assembly of pentacene molecules on graphene formed on a 6H-SiC (0001) substrate by scanning tunneling microscopy. At sub-monolayer coverage, adsorption of pentacene molecules on epitaxial graphene is affected by $6{\times}6$ pattern originates from the underlying buffer layer. And the orientation of pentacene in the ordered structure is aligned with the zigzag direction of the edge structure of single layer graphene. As coverage increased, intermolecular interactions become stronger than molecule-substrate interaction. As a result, herringbone structures the consequence of higher intermolecular interaction are observed.

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A Study on the Optimal Method for Mal-function of Re-closer at the Distribution Feeders Interconnected with PV Systems (태양광발전이 연계된 배전계통의 보호기기 오동작에 대한 최적 운용방안에 관한 연구)

  • Kim, Chan-Hyeok;Park, Hyeon-Seok;Rho, Dea-Seok;Shin, Chang-Hoon;Yoon, Gi-Gab
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.8
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    • pp.1512-1518
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    • 2009
  • Recently, new dispersed power sources such as photovoltaics, wind power, fuel cell etc. are energetically interconnected and operated in the distribution systems, as one of the national projects for alternative energy. This paper deals with the optimal countermeasures for the mal-function of protective devices at primary feeder in distribution systems when new power sources like photovoltaic (PV) systems are interconnected, based on the symmetrical components of short circuit studies. When new power sources are considered to be interconnected to distribution systems, bi-directional power flow and interconnection transformer connection of new power sources may cause the operation problems of protective devices (mainly re-closer), since new power sources can change typical characteristics of distribution systems. Therefore, this paper shows an analysis skill of the mal-functional mechanism of protective relay and proposes the optimal solution for the mal-function problem using the symmetrical components of fault analysis. And, this paper also shows the effectiveness of proposed method by the simulation at the field distribution systems.

A Study of Field-Ring Design using a Variety of Analysis Method in Insulated Gate Bipolar Transistor (IGBT)

  • Jung, Eun Sik;Kyoung, Sin-Su;Chung, Hunsuk;Kang, Ey Goo
    • Journal of Electrical Engineering and Technology
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    • v.9 no.6
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    • pp.1995-2003
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    • 2014
  • Power semiconductor devices have been the major backbone for high-power electronic devices. One of important parameters in view of power semiconductor devices often characterize with a high breakdown voltage. Therefore, many efforts have been made, since the development of the Insulated Gate Bipolar Transistor (IGBT), toward having higher level of breakdown voltage, whereby the typical design thereof is focused on the structure using the field ring. In this study, in an attempt to make up more optimized field-ring structure, the characteristics of the field ring were investigated with the use of theoretical arithmetic model and methodologically the design of experiments (DOE). In addition, the IGBT having the field-ring structure was designed via simulation based on the finding from the above, the result of which was also analyzed. Lastly, the current study described the trench field-ring structure taking advantages of trench-etching process having the improved field-ring structure, not as simple as the conventional one. As a result of the simulation, it was found that the improved trench field-ring structure leads to more desirable voltage divider than relying on the conventional field-ring structure.

Low-Temperature Solution Process of Al-Doped ZnO Nanoflakes for Flexible Perovskite Solar Cells

  • Nam, SeongSik;Vu, Trung Kien;Le, Duc Thang;Oh, Ilwhan
    • Journal of Electrochemical Science and Technology
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    • v.9 no.2
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    • pp.118-125
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    • 2018
  • Herein we report on the selective synthesis and direct growth of nanostructures using an aqueous chemical growth route. Specifically, Al-doped ZnO (AZO) nanoflakes (NFs) are vertically grown on indium tin oxide (ITO) coated flexible polyethylene terephthalate (PET) sheets at low temperature and ambient environment. The morphological, optical, and electrical properties of the NFs are investigated as a function of the Al content. Furthermore, these AZO-NFs are integrated into perovskite solar devices as the electron transport layer (ETL) and the fabricated devices are tested for photovoltaic performance. It was determined that the doping of AZO-NFs significantly increases the performance metrics of the solar cells, mainly by increasing the short-circuit current of the devices. The observed enhancement is primarily attributed to the improved conductivity of the doped AZO-NF, which facilitates charge separation and reduces recombination. Further, our flexible solar cells fabricated through this low temperature process demonstrate an acceptable reproducibility and stability when exposed to a mechanical bending test.

Novel Optical Properties of Si Nanowire Arrays

  • Lee, Munhee;Gwon, Minji;Cho, Yunae;Kim, Dong-Wook
    • Proceedings of the Korean Vacuum Society Conference
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    • 2014.02a
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    • pp.179.1-179.1
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    • 2014
  • Si nanowires have exhibited unique optical characteristics, including nano-antenna effects due to the guided mode resonance, significant optical absorption enhancement in wide wavelength and incident angle range due to resonant optical modes, graded refractive index, and scattering. Since Si poor optical absorption coefficient due to indirect bandgap, all such properties have stimulated proposal of new optoelectronic devices whose performance can surpass that of conventional planar devices. We have carried out finite-difference time-domain simulation studies to design optimal Si nanowire array for solar cell applications. Optical reflectance, transmission, and absorption can be calculated for nanowire arrays with various diameter, length, and period. From the absorption, maximum achievable photocurrent can be estimated. In real devices, serious recombination loss occurring at the surface states is known to limit the photovoltaic performance of the nanowire-based solar cells. In order to address such issue, we will discuss how the geometric parameters of the array can influence the spatial distribution of the optical field (resulting optical generation rate) in the nanowires.

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Hierarchical Nanostructure on Glass for Self Cleaning and Antireflective Properties

  • Xiong, Junjie;Das, Sachindra Nath;Kar, Jyoti Prakash;Choi, Ji-Hyuk;Myoung, Jae-Min
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2010.05a
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    • pp.24.1-24.1
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    • 2010
  • In practical operation, the exposed surfaces may get dirty thus degrade the performance of devices. So the combination of self cleaning and antireflection is very desirable for use in outdoor photovoltaic and displaying devices, self cleaning windows and car windshields. For the purpose of self cleaning, the surface needs to be either superhydrophobic or superhydrophilic. However, in practice AR in the visible region and self cleaning are a pair of competitive properties. To satisfy the requirements for superhydrophobic or superhydrophilic surfaces, high surface roughness is required. But it usually cause severely light scattering. Photo-responsive coatings (TiO2, ZnO etc.) can lead to superhydrophilic. However, the refractive indices are high. Thus for porous structure, controlling pore size in the underwavelength scale to reduce the light scattering is very crucial for highly transparent and self cleaning antireflection coating. Herein, we demonstrate a simple method to make high performance broadband antireflection layer on the glass surface, by "carving" the surface by hot alkali solution. Etched glass has superhydrophilic surface. By chemical modification, it turns to superhydrophobic. Enhanced transparency (up to 97%) in a broad wavelength range was obtained by short time etching. Also antifogging effect has been demonstrated, which may offer advantage for devices working at high humidity environment or underwater. Compositional dependence of the properties was observed by comparing three different commercially available glasses.

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Melt-Crystal Interface Shape Formation by Crystal Growth Rate and Defect Optimization in Single Crystal Silicon Ingot (단결정 실리콘 잉곳 결정성장 속도에 따른 고-액 경계면 형성 및 Defect 최적화)

  • Jeon, Hye Jun;Park, Ju Hong;Artemyev, Vladimir;Jung, Jae Hak
    • Current Photovoltaic Research
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    • v.8 no.1
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    • pp.17-26
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    • 2020
  • It is clear that monocrystalline Silicon (Si) ingots are the key raw material for semiconductors devices. In the present industries markets, most of monocrystalline Silicon (Si) ingots are made by Czochralski Process due to their advantages with low production cost and the big crystal diameters in comparison with other manufacturing process such as Float-Zone technique. However, the disadvantage of Czochralski Process is the presence of impurities such as oxygen or carbon from the quartz and graphite crucible which later will resulted in defects and then lowering the efficiency of Si wafer. The heat transfer plays an important role in the formation of Si ingots. However, the heat transfer generates convection in Si molten state which induces the defects in Si crystal. In this study, a crystal growth simulation software was used to optimize the Si crystal growth process. The furnace and system design were modified. The results showed the melt-crystal interface shape can affect the Si crystal growth rate and defect points. In this study, the defect points and desired interface shape were controlled by specific crystal growth rate condition.

Fabrication and Characterization of Electro-photonic Performance of Nanopatterned Organic Optoelectronics

  • Nil, Ri-Swi;Han, Ji-Yeong;Gwon, Hyeon-Geun;Lee, Gyu-Tae;Go, Du-Hyeon
    • Proceedings of the Korean Vacuum Society Conference
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    • 2014.02a
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    • pp.134.2-134.2
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    • 2014
  • Photonic crystal solar cells have the potential for addressing the disparate length scales in polymer photovoltaic materials, thereby confronting the major challenge in solar cell technology: efficiency. One must achieve simultaneously an efficient absorption of photons with effective carrier extraction. Unfortunately the two processes have opposing requirements. Efficient absorption of light calls for thicker PV active layers whereas carrier transport always benefits from thinner ones, and this dichotomy is at the heart of an efficiency/cost conundrum that has kept solar energy expensive relative to fossil fuels. This dichotomy persists over the entire solar spectrum but increasingly so near a semiconductor's band edge where absorption is weak. We report a 2-D, photonic crystal morphology that enhances the efficiency of organic photovoltaic cells relative to conventional planar cells. The morphology is developed by patterning an organic photoactive bulk heterojunction blend of Poly(3-(2-methyl-2-hexylcarboxylate) thiophene-co-thiophene) and PCBM via PRINT, a nano-embossing method that lends itself to large area fabrication of nanostructures. The photonic crystal cell morphology increases photocurrents generally, and particularly through the excitation of resonant modes near the band edge of the organic PV material. The device performance of the photonic crystal cell showed a nearly doubled increase in efficiency relative to conventional planar cell designs. Photonic crystals can also enhance performance of other optoelectronic devices including organic laser.

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Electric Power Charging of Silicon Solar Cells using a Laser (레이저 조사에 따른 실리콘 솔라셀의 출력 특성)

  • Lee, Hu-Seung;Bae, Han-Sung;Kim, Seongbeom;Joo, Yun-Jae;Kim, Jung-Oh;Noh, Ji-Hwan
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.25 no.5
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    • pp.362-367
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    • 2016
  • Recently, wireless charging systems have expanded their applications from household electrical appliances to outdoor activity devices. In wireless charging systems, solar cells have versatile advantages, such as abundant raw materials within the earth, reasonable prices of products, and highest power conversion efficiency. In this study, the photovoltaic effect between a silicon solar cell and a photon of infrared wavelength was simulated using a Shockley diode equation. A solar cell power charging system was then set up to: 1) clarify mechanisms of the charging interaction based on the photovoltaic effect with a laser source, and 2) verify interdependency of the parameters: laser settings and geometrical position between a solar cell and the laser. As was observed, the solar cell generates more power when the photon was irradiated uniformly, intensively, and vertically on the surface of the solar cell.

Enhancement in Open-circuit Voltage of Methylammmonium Lead Halide Perovskite Solar Cells Via Non-stoichiometric Precursor (비화학양론적 전구체 조성 조절을 통한 페로브스카이트 태양전지의 개방전압 향상)

  • Yun, Hee-Sun;Jang, Yoon Hee;Lee, Doh-Kwon
    • Current Photovoltaic Research
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    • v.6 no.1
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    • pp.12-16
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    • 2018
  • The interest in perovskite solar cells has been skyrocketed owing to their rapid progress in efficiency in recent years. Here, we report the effect of non-stoichiometry in the methylammonium lead trihalide ($MAPbI_3$) precursors used in a solution process with different MAI : $PbI_2$ ratios of 1 : 0.96, 1 : 1.10, 1 : 1.15, and 1:1.20. With an increase in the $PbI_2$ content, the $PbI_2$ secondary phase was found to form at grain boundary region of perovskite thin films, as evidenced by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In terms of device performance, open-circuit voltage in particular is significantly improved with increasing the molar ratio of $PbI_2$, which is possibly ascribed to the reduction in recombination sites at grain boundary of perovskite and hence the prolonged life time of light-generated carriers according to the reported. As a result, the $PbI_2-excess$ devices exhibited a higher power conversion efficiency compared to the MAI-excess ones.