• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.181-184
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• 2004

Organic semiconductors have attracted considerable attention due to their interesting physical properties followed by various technological applications in the area of electronics and opto-electronics. It has been a long time since organic solar cells were expected as a low-cost high-energy conversion device. Although practical use of them has not been achieved, technological progress continues. Morphology of the materials, organic/inorganic interface, metal cathodes, molecular packing and structural properties of the donor and acceptor layers are essential for photovoltaic response. We have fabricated solar-cell devices based on copper-phthalocyanine(CuPc) as a donor(D) and fullerene($C_{60}$) as an electron acceptor(A) with doped charge transport layers, and BCP as an exciton blocking layer(EBL). We have measured photovoltaic characteristics of the solar-cell devices using the xenon lamp as a light source.

• 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.

• Current Photovoltaic Research
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• v.4 no.2
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• pp.48-53
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• 2016

We report the effect of physical load on the stability of organic solar cells under physical loads. The active layers in organic solar cells were fabricated with bulk heterojunction films (BHJ) films of poly (3-hexylthiophene) and phenyl-$C_{61}$-butyric methyl ester. The loading time was varied up to 60 s by keeping the physical load constant. Results showed that the open circuit voltage was not influenced by the physical load but other solar cell parameters were sensitive to the loading time. The fill factor was very slightly increased at 15 s, while short circuit current density was well kept for 30 s. The power conversion efficiency was reasonably maintained for 45 s but became significantly decreased by the continuous loading for 60 s.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.190.2-190.2
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• 2014

We report the origin of the improvement of the power conversion efficiency (PCE) of hybrid thin-film solar cells when a soluble C60 derivative, [6,6]-phenyl-$C_{61}$-butyric acid methyl ester (PCBM), is introduced as a hole-blocking layer. The PCBM layer could establish better interfacial contact by decreasing the reverse ark-saturation current density, resulting in a decrease in the probability of carrier recombination. The power conversion efficiency of this optimized device reached a maximum value of 8.34% and is the highest yet reported for hybrid thin-film solar cells.

• Journal of Information Display
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• v.12 no.3
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• pp.145-152
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• 2011

Since the discovery of fullerenes as a class of nanostructure compounds, many potential applications have been suggested for their unusual structures and properties. The isolated pentagon rule (IPR) states that all pentagonal carbon rings are isolated in the most stable fullerene. Fullerenes $C_n$ are a class of spherical carbon allotrope group with unique properties. Electron transfer between fullerenes and other molecules is thought to involve the transfer of electrons between the molecules surrounding the fullerene cage. One class of electron transfer molecules is the methanofullerene derivatives ([6,6]-phenyl $C_{61}$-butyric acid methyl ester (PCBM), 4-(2-ethylhexyloxy)-[6,6]-phenyl $C_{61}$-butyric acid methyl ester (p-EHO-PCBM), and 4-(2-ethylhexyloxy)-[6,6]-phenyl $C_{61}$-butyric acid (p-EHO-PCBA), 10-12). It has been determined that $C_{60}$ does not obey IPR. Supramolecular complexes 1-9 and 10-12 are shown to possess a previously unreported host.guest interaction for electron transfer processes. The unsaturated, cis-geometry, thiocrown ethers, (1-9) (described as [X-UT-Y], where X and Y indicate the numbers of carbon and sulfur atoms, respectively), are a group of crown ethers that display interesting physiochemical properties in the light of their conformational restriction compared with a corresponding saturated system, as well as the sizes of their cavities. Topological indices have been successfully used to construct mathematical methods that relate structural data to various chemical and physical properties. To establish a good relationship between the structures of 1-9 with 10-12, a new index is introduced, ${\mu}_{cs}$. This index is the ratio of the sum of the number of carbon atoms ($n_c$) and the number of sulfur atoms ($n_s$) to the product of these two numbers for 1-9. In this study, the relationships between this index and oxidation potential ($^{ox}E_1$) of 1-9, as well as the first to third free energies of electron transfer (${\Delta}G_{et(n)}$, for n = 1-3, which is given by the Rehm-Weller equation) between 1-9 and PCBM, p-EHO-PCBM, and p-EHO-PCBA (10-12) as [X-UT-Y]@R(where R is the adduct PCBM, p-EHO-PCBM, and p-EHO-PCBA group) (13-15) supramolecular complexes are presented and investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.449-449
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• 2010

유기발광소자(organic light-emitting diodes, OLEDs)는 저공정비용, 경량화, 가용성 및 대면적화 등의 장점으로 조명 분야와 디스플레이 분야로의 응용 가능성으로 인해 크게 주목을 받아 왔다. 이러한 OLED 소자의 고효율, 고휘도 및 저소비전력 등을 구현하기 위해서는 전극으로부터 전하 주입 층으로 효율적인 전하 주입이 요구된다. 즉, 각 전극의 폐르미 준위로부터 전하 전도준위대로의 전하주입 장벽이 없어야 한다. 본 연구에서는 홀 주입장벽이 없는 정공주입 층으로 $MoO_x$(molybdenum oxide)가 도핑된 NPB(N, N'-diphenyl-N, N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine) 층을 사용하여 hole-only 소자를 제작하고 전류-전압 특성을 통해 양극으로부터 홀주입 층으로의 hole-ohmic 특성을 고찰했다. 또한, 전자 주입장벽이 없는 전자주입 층으로 $C_{60}$(fullerene)/LiF(lithum fluoride)의 이종 층을 사용하여 electron-only 소자를 제작하고 음극으로부터 전자주입 층으로의 전자 ohmic 특성을 조사했다. 또한, 전극으로부터 전하주입 층으로 ohmic 특성을 더 자세히 이해하기 위하여 전하주입 층의 자외선 광방출 스펙트럼(ultraviolet photoemission spectra)을 조사했다. 한편, glass/ITO/$MoO_x$-doped NPB (x%: x=0,25, 50 및 75; 5nm)/NPB (63nm)/$Alq_3$ (37nm)/$C_{60}$ (5nm)/LiF (1nm)/Al (100nm)로 구성된 all-ohmic OLED 소자의 발광특성은 $MoO_x$의 도핑 농도가 25%이상일 때 최적의 특성을 보여줬다. 이러한 현상은 정공주입 층에서 p형 도핑 농도의 증가에 따른 정공 농도의 증가에 기인한다. 또한 $MoO_x$의 도핑 농도의 증가에 따라 정공주입 층의 new gap state와 전극의 페르미 준위의 pinning에 기인한다. 25%의 $MoO_x$을 가진 OLED소자는 7.2V의 낮은 전압에서 $58300 cd/m^2$의 높은 휘도를 보여줬다.

• Bulletin of the Korean Chemical Society
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• v.31 no.5
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• pp.1128-1134
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• 2010

Nanocarbon supported Fe/$TiO_2$ composite catalysts were prepared using CNTs (carbon nanotubes) and $C_{60}$ (fullerene) as nanocarbon sources by a modified sol-gel method. The Fe/$TiO_2$-nanocarbon composites were characterized by the BET surface area, scanning electron microscope (SEM), Transmission Electron Microscope (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and UV-vis spectra. In comparison with non-nanocarbon doped Fe/$TiO_2$ composites, the nanocarbon supported Fe/$TiO_2$ composites had higher absorption ability with a larger specific surface area, and showed higher photocatalytic activity during the degradation of methylene blue (MB) under visible light. The reasons for the obvious increase of photocatalytic activity indicated that the photoactivity not only benefits from nanocarbon introduced, but also relates to the cooperative effect of the Fe as a dopant.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.17.1-17.1
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• 2010

2000년대 들어 소재기술의 진보와 함께 혁신적인 성능개선이 이뤄지고 있는 유기박막 태양전지는 가장 신형의 3세대 태양전지로서, 유기 재료의 손쉬운 가공성과 다양성, 낮은 재료비, 그리고 프린팅, 코팅 공정과 같은 값싼 소자 제작공정으로 인해 차세대 저가 태양전지로서 큰 기대를 모으고 있다. 현재 유기박막 태양전지는 단위소자 기준으로 7%대의 광전변환 효율을 달성하고 있는데, 다양한 반도체성 고분자나 단분자 도너 물질에 특히 전자 수용성이 좋은 fullerene(C60)계 억셉터 물질을 채택함으로써 급격히 성능 개선이 이뤄지고 있다. 그러나 상용화를 위해서는 궁극적으로 대면적에서 10% 이상의 성능 수준이 요구되는 바, 유기재료의 낮은 전하 이동도와 짧은 수명을 극복하고 성능을 극대화하기 위해서는 고성능 신규소재의 개발이 필수이다. 태양광 스펙트럼의 장파장 까지 빛흡수가 가능하면서도 광흡수계수가 높은 저밴드갭 도너 물질, 전하 이동도가 획기적으로 개선되고 광 안정성도 높은 신규 소재 개발이 일차적으로 요구되며, 박막 특성 개선과 소자구조의 최적화 등에서도 보다 광범위한 연구개발이 요구되고 있다. 특히 저가의 용액공정에 의한 소자 제작시 박막의 나노-모폴로지 제어는 소자의 성능에 지대한 영향을 미치므로 공정별 한계와 최적조건을 구축하는 것도 매우 긴요하다. 본 발표에서는 당 연구팀을 포함한 국내외 연구그룹들의 최근 유기박막 태양전지 신소재 개발 및 용액공정 기술 현황에 대하여 간략히 살펴보고자 한다.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.488-490
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• 2010

최근 심각한 환경오염 문제와 화석 에너지 고갈로 차세대 청정 에너지 개발에 대한 중요성이 증대되고 있다. 그중에서 태양정지는 공해가 적고, 자원이 무한적이며 반 영구적인 수명을 가지고 있어 미래에너지 문제를 해결할 수 있는 에너지원으로 기대되고 있다. 본 연구에서는 P3HT(regioregular poly(3-hexylthiophene))와 PCBM(fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester)을 전자 도너와 억셉터 물질을 하나의 브랜드로 광 활성층을 형성하는 BHJ(bulk hetero junction)구조를 갖는 고분자 유기 박막 태양전지를 각각 Toluene, Mono-Chlorobenzene, Dichlorobenzene에 $60^{\circ}C$, 200rpm으로 약 12시간동안 1wt%로 교반(Stirring)한 후에 중량비(1:1 wt%)로 혼합하여 스핀코팅(Spin-coating)으로 제작하였고, 완성된 소자의 광활성층 면적은 0.04cm2이며, $150^{\circ}C$에서 후속 열처리 공정을 통해 특성 향상이 측정 되었다. 태양전지 소자 구조는 Glass / ITO / PEDOT:PSS / P3HT : PCBM / Al이다. 전류-전압, FF(Fill Factor), 변환효율 측정을 위해 solar simulator를 AM1.5 조건(100 mW/cm2)으로 이용하였으며, 소자의 최대 전류밀도는 12mA/$cm^2$, 개방전압은 0.566V이고 F.F(Fill Factor)는 55.2%이고 변환효율은 3.7%이다. 후속 열처리후 더욱 좋은 성능을 갖게 되었고, 최대 효율은 Dichl orobenzene일 때 이다.

• Journal of the Korean Vacuum Society
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• v.14 no.1
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• pp.40-48
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• 2005

Bucky shuttle memory systems were investigated by the classical molecular dynamics(MD) simulations. Energetics and operating response of the shuttle-memory-elements u?ere examined by MD simulations of the C/sub 60/ shuttle in the nanomemory systems under various external force fields. Single-nanopeapod type was consisting of three fullerenes encapsulated in (10, 10) boron-nitride nanotube and filled Cu electrode. Studied systems could be applied to nonvolatile memory. MD simulation results showed that the stable bit flops could be achieved from the external force fields of 0.1 eV/Å for single-nanopeapod type.