• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1154-1155
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• 2008

본 연구에서는 전자 주개 물질(electron donor)인 regioregular poly(3-hexylthiophene)(P3HT)와 전자 받개 물질(electron acceptor)인 phenyl-$C_{61}$-butyric acid methyl ester (PCBM)을 혼합한 복합 박막 구조(Bulk Heterojunction)를 이용하여 태양전지를 제작하고 광활성층(Active layer)의 두께를 변화시키면서 광학적 특성 및 전기적 특성에 대해 분석하였다. 광활성층의 두께가 두꺼워 질수록 광흡수율이 높기 때문에 태양전지의 효율이 증가하여 200nm정도의 두께에서 가장 좋은 특성을 보였으며, 그 이상의 두께에서는 광흡수율이 높더라도 직렬저항(Series resistance)의 증가로 개방 회로 전압이 감소하는 것을 볼 수 있었으며, 최적화된 광활성층의 두께(190nm)에서 개방 회로 전압($V_{oc}$)은 0.6V, 단락 회로 전류($J_{sc}$)는 8.29mA, Fill factor(FF)는 0.59, 전력변환효율($\eta$)은 2.94%였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.275.1-275.1
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• 2014

The effects of the interfacial buffer layer and temperature on the organic bulk heterojunction (BHJ) nanostructures of copper phthalocyanine (CuPc) and fullerene (C60) systems were investigated using real time in-situ x-ray scattering. In the CuPc:C60 BHJ structures, standing-on configured ${\gamma}$-CuPc phase was formed by co-deposition of CuPc and C60. Once formed ${\gamma}$-phase was thermally stable during the annealing upon $180^{\circ}C$. Meanwhile, the insertion of CuI buffer layer prior to deposition of the CuPc:C60 BHJ layer induced lying-down configured CuPc crystals in the BHJ layer. The lying CuPc peak intensity and the lattice parameter were increased by the thermal annealing. This increment of the intensity seemed to be related to the strain at the interface between CuPc:C60 and CuI, which was proportional to the enhancement of the power conversion efficiency of the device.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.329-329
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• 2011

We investigated the thin films of poly(3-hexylthiophene) (P3HT) and C61-butyric acid methylester (PCBM) prepared by ultrahigh vacuum (UHV) electrospray depositioin (ESD) by using in-situ XPS, UPS and ambient-pressure AFM. The morphology, chemical structures, and interface properties of these materials, most widely used for bulk heterojunction organic solar cells, were studied depending on the ESD solution compositions and concentrations. We found that the solution conductivity and flow rate as well as applied voltage are the important parameters for stable electrospray and film formation. These results suggest that UHV ESD is a viable method for the deposition of multilayers of polymers under UHV condition. We also discuss the energy level alignment for the various deposition conditions at the interface, which is one of the most important operating parameters of the bulk heterojunction organic solar cells.

• Korean Journal of Materials Research
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• v.33 no.6
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• pp.236-241
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• 2023

Solar cells based on p-conjugated donor-acceptor (D-A) organic molecular systems are a promising alternative to conventional electrical energy generation. D-A molecular systems, which have a triphenylamine (TPA) moiety linked with a benzothiadiazole (BTD) moiety, open the potential development of new small molecule donors for bulk heterojunction (BHJ) solar cells. Here, a series of donor-acceptor-π-acceptor (D-A-π-A) small molecule donors (SMD) derived from triphenylamine (TPA) donor and benzothiadiazole (BTD) acceptor building blocks, were designed for BHJ organic solar cells. The small molecule donors SMD1-4 were studied using density functional theory (DFT) and time dependent-DFT (TDDFT) methods, to understand the effect of cyano and fluorine group functionalization on their properties. The effect of structure alteration by cyano and fluorine group functionalization on the optoelectronic properties, the calculated highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) and the HOMO-LUMO gaps were theoretically explored. The V_oc (open-circuit photovoltage) and fill factor (FF) for SMD1-4 were obtained with a PC₇₁BM acceptor, which showed that these organic small molecules are potential small molecule donors for organic bulk heterojunction solar cells.

• Journal of Electrical Engineering and information Science
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• v.2 no.4
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• pp.99-105
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• 1997

The new classified model for N-p heterojunction diode is derived and used extensively in analyzing the current-voltage(I-V) characteristics of the HBTs. A new classification method is presented in order to simplify I-V equations and easily applied to the modeling of HBTs. This classification method is characterized by the properties of devices such as high level injection, the thickness of one or both bulk regions, the surface recombination and the generation-recombination. The simulation results using the proposed model agree well with the experimentally observed I-V behaviors and show good efficiencies in its application to HBTs with respect to mathematical formulation.

• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3845-3848
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• 2012

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.661-664
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• 2013

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.20-20
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• 2010

Organic based photovoltaics (OPV) have been received a lot of attention because they are lightweight, inexpensive to fabricate and flexible compare to crystalline Si solar cells. In this seminar, several important progresses in the Polymer PV, such as, formation of bulk heterojunction, development of post annealing technique, tandem cell fabrication will be introduced. In addition that, some efforts to achieve the further improvement in the performance of the Polymer PV will be discussed.

• Journal of the Korean GEO-environmental Society
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• v.24 no.3
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• pp.23-27
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• 2023

Graphitic carbon nitride (g-C₃N₄) has been used as effective photocatalyst for degradation of antibiotics under visible light irradiation. However, the fast recombination of hole-electron pair may limit their photocatalytic efficiency. In our study, Ag was grafted on g-C₃N₄/g-C₃N₄ isotype heterojunction by a microwave-assisted decomposition method. The structure and physical properties of heterojunction photocatalyst were characterized through X-ray diffraction, UV-DRS, FT-IR, and Photoluminescence analyses. Ag decorated g-C₃N₄/g-C₃N₄ isotype heterojunction exhibited excellent photocatalytic activity for degradation of sulfamethoxazole under irradiation under visible light irradiation within 210 min, which is higher than g-C₃N₄/g-C₃N₄ isotype heterojunction and bulk g-C₃N₄. The addition of Ag may broaden the visible light absorption and restrict the recombination of hole-electron pair because of the surface plasmons resonance, resulting in the improving the photocatalytic activity.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.73-73
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• 2011

We will report a few methods to improve the efficiency and stability in small molecule based organic solar cells, including the formation of bulk heterojunctions (BHJs) through alternative thermal deposition (ATD), the use of a micro-cavity structure and interface modifications. By ATD which is a simple modification of conventional thermal evaporation, the thicknesses of alternative donor and acceptor layers were precisely controlled down to 0.1 nm, which is critical to form BHJs. The formation of a BHJ in copper(II) phthalocyanine (CuPc) and fullerene (C60) systems was confirmed by AFM, GISAXS and absorption measurements. From analysis of the data, we found that the CuPc|C60 films fabricated by ATD were composed of the nanometer sized disk shaped CuPc nano grains and aggregated C60, which explains the phase separation of CuPc and C60. On the other hand, the co-deposited CuPc:C60 films did not show the existence of separated CuPc nano grains in the CuPc:C60 matrix. The OPV cells fabricated using the ATD method showed significantly enhanced power conversion efficiency compared to the co-deposited OPV cells under a same composition [1]. We will also present by numerical simulation that adoption of microcavity structure in the planar heterojunction can improve the short circuit current in single and tandem OSCs [2]. Interface modifications also allowed us to achieve high efficiency and high stability OSCs.