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Alternative transparent electrodes for Low-cost, flexible small-molecule organic solar cells
김용현,( Lars Muller Meskamp ),( Karl Leo ) 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0
In recent years, there has been a rapid progress in the development of small-molecule organic photovoltaic cells with the power conversion efficiency reaching 12.0%. Besides high efficiency, the development of transparent conducting electrodes is of great importance for low cost and flexible organic solar cells. In this work, we have developed lowcost, efficient, semi-transparent small-molecule organic solar cells based on various alternative transparent electrodes, such as highly conductive polymers, ZnO, carbon nanotubes, doped C60, and conducting polymer/metal grid electrodes. These devices are carefully optimized by doping techniques for electrodes and interfacial layers. These results demonstrate that small-molecule organic solar cells based on alternative electrodes, optimized by doping technologies, have a promising future for practical applications in efficient, low-cost, flexible and semi-transparent device manufacturing.
PEDOT:PSS 투명전극의 솔벤트 도핑 농도와 홀 이동층의 두께에 따른 유기태양전지의 특성 연구
김용현 ( Yong Hyun Kim ),( Lars Muller Meskamp ),( Karl Leo ) 한국화상학회 2014 한국화상학회지 Vol.20 No.4
유기태양전지의 투명전극으로서 기존의 값비싸고 깨지기 쉬운 Indium Tin Oxide (ITO) 전극을 대체하고자, 전도성 고분자인 poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)를 적용하였다. 솔벤트의 도핑농도에 따른 PEDOT:PSS 박막의 전기 전도도와 표면 거칠기의 특성 변화를 관찰하고, 그 결과가 PEDOT:PSS를 투명전극으로 사용한 유기태양전지의 특성에 미치는 영향을 연구하였다. PEDOT:PSS의 솔벤트 농도가 증가함에 따라, 박막의 표면 거칠기가 증가하고, 이는 유기태양전지의 단락전류의 변화를 야기했다. 또한, 소자의 홀 이동층이 얇아짐에 따라 광활성층의 단파장영역의 광흡수가 증가하는 것을 관찰할 수 있었다. Indium tin oxide (ITO) is the most common transparent electrode for organic solar cells due to its high electrical conductivity and transmittance. However, the ITO film significantly increases device costs and its brittleness limits the applications in flexible electronics. Here, a highly conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is studied as an alternative electrode for organic solar cells. The effect of solvent doping concentration on the electrical and surface structural properties of PEDOT:PSS thin films is investigated. It is observed that, with increasing a solvent concentration in PEDOT:PSS films, surface roughness of PEDOT:PSS electrodes increases, causing the change of short circuit current densities in devices. In addition, a light absorption property at short wavelengths is enhanced by decreasing the thickness of hole transport layers of organic solar cells.
Lee, Jonghee,Koh, Tae-Wook,Cho, Hyunsu,Hofmann, Simone,Reineke, Sebastian,Lee, Jae-Hyun,Lee, Jeong-Ik,Yoo, Seunghyup,Leo, Karl,Gather, Malte C. Elsevier 2015 Organic Electronics Vol.26 No.-
<P><B>Abstract</B></P> <P>White organic light-emitting diodes (WOLEDs) are one of the most promising technologies to realize future solid-state lighting with high power efficiency, broad and adjustable spectral coverage, and area emission for more effective and natural illumination. In this work, we report a new method of tuning the correlated color temperature (CCT) of WOLEDs via spatially controlling the degree of the micro-cavity effect in an OLED. Varying the width of thin Ag strips deposited on top of a transparent electrode leads to changes in both intensity and phase of reflection at the anode, hence significantly altering emission spectra of proposed WOLEDs. CCT of the implemented WOLEDs span a wide range, from 3000K to 8000K, demonstrating that our proposed approach helps to meet the need for lighting with various CCTs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We report a correlated color temperature (CCT) tunable white OLEDs. </LI> <LI> Micro-cavity (MC) effect in an OLED was controlled with a striped thin metal layer. </LI> <LI> MC effect alters emission spectra and intensity of white OLEDs. </LI> <LI> CCT of the implemented white OLEDs span a wide range, from 3000K to 8000K. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>White organic light-emitting diodes (WOLEDs) are one of the most promising technologies to realize future solid-state lighting with high power efficiency, broad and adjustable spectral coverage, and area emission for more effective and natural illumination. In this work, we report a new method of tuning the correlated color temperature (CCT) of WOLEDs via spatially controlling the degree of the micro-cavity effect in an OLED. Varying the width of thin Ag strips deposited on top of a transparent electrode leads to changes in both intensity and phase of reflection at the anode, hence significantly altering emission spectra of proposed WOLEDs. CCT of the implemented WOLEDs span a wide range, from 3000K to 8000K, demonstrating that our proposed approach helps to meet the need for lighting with various CCTs.</P> <P>[DISPLAY OMISSION]</P>
Organic Zener Diodes: Tunneling across the Gap in Organic Semiconductor Materials
Kleemann, Hans,Gutierrez, Rafael,Lindner, Frank,Avdoshenko, Stanislav,Manrique, Pedro D.,Lü,ssem, Bjö,rn,Cuniberti, Gianaurelio,Leo, Karl American Chemical Society 2010 Nano letters Vol.10 No.12
<P>Organic Zener diodes with a precisely adjustable reverse breakdown from −3 to −15 V without any influence on the forward current−voltage curve are realized. This is accomplished by controlling the width of the charge depletion zone in a pin-diode with an accuracy of one nanometer independently of the doping concentration and the thickness of the intrinsic layer. The breakdown effect with its exponential current voltage behavior and a weak temperature dependence is explained by a tunneling mechanism across the highest occupied molecular orbital−lowest unoccupied molecular orbital gap of neighboring molecules. The experimental data are confirmed by a minimal Hamiltonian model approach, including coherent tunneling and incoherent hopping processes as possible charge transport pathways through the effective device region.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-12/nl102916n/production/images/medium/nl-2010-02916n_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl102916n'>ACS Electronic Supporting Info</A></P>
Kim, Yong Hyun,Lee, Jonghee,Hofmann, Simone,Gather, Malte C.,Mü,ller‐,Meskamp, Lars,Leo, Karl WILEY‐VCH Verlag 2013 Advanced functional materials Vol.23 No.30
<P><B>Abstract</B></P><P>Efficient transparent organic light‐emitting diodes (OLEDs) with improved stability based on conductive, transparent poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes are reported. Based on optical simulations, the device structures are carefully optimized by tuning the thickness of doped transport layers and electrodes. As a result, the performance of PEDOT:PSS‐based OLEDs reaches that of indium tin oxide (ITO)‐based reference devices. The efficiency and the long‐term stability of PEDOT:PSS‐based OLEDs are significantly improved. The structure engineering demonstrated in this study greatly enhances the overall performances of ITO‐free transparent OLEDs in terms of efficiency, lifetime, and transmittance. These results indicate that PEDOT:PSS‐based OLEDs have a promising future for practical applications in low‐cost and flexible device manufacturing.</P>
Enhanced and balanced efficiency of white bi-directional organic light-emitting diodes.
Lee, Jonghee,Cho, Hyunsu,Koh, Tae-Wook,Yun, Changhun,Hofmann, Simone,Lee, Jae-Hyun,Kim, Yong Hyun,L?ssem, Bj?rn,Lee, Jeong-Ik,Leo, Karl,Gather, Malte C,Yoo, Seunghyup Optical Society of America 2013 Optics express Vol.21 No.23
<P>We report on the characteristics of enhanced and balanced white-light emission from bi-directional organic light-emitting diodes (BiOLEDs) enabled by the introduction of micro-cavity effects. The insertion of an additional metal layer between the indium tin oxide anode and the hole transporting layer results in similar light output of our BiOLEDs in both top and bottom direction and in reduced distortion of the electroluminescence spectrum. Furthermore, we find that by utilizing MC effects, the overall current efficiency can be improved by 26.2% compared to that of a conventional device.</P>
Kim, Yong Hyun,Kim, Jin Soo,Kim, Won Mok,Seong, Tae‐,Yeon,Lee, Jonghee,Mü,ller‐,Meskamp, Lars,Leo, Karl WILEY‐VCH Verlag 2013 Advanced functional materials Vol.23 No.29
<P><B>Abstract</B></P><P>High performance indium tin oxide (ITO)‐free small molecule organic solar cells and organic light‐emitting diodes (OLEDs) are demonstrated using optimized ZnO electrodes with alternative non‐metallic co‐dopants. The co‐doping of hydrogen and fluorine reduces the metal content of ZnO thin films, resulting in a low absorption coefficient, a high transmittance, and a low refractive index as well as the high conductivity, which are needed for the application in organic solar cells and OLEDs. While the established metal‐doped ZnO films have good electrical and optical properties, their application in organic devices is not as efficient as other alternative electrode approaches. The optimized ZnO electrodes presented here are employed in organic solar cells as well as OLEDs and allow not only the replacement of ITO, but also significantly improve the efficiency compared to lab‐standard ITO. The enhanced performance is attributed to outstanding optical properties and spontaneously nanostructured surfaces of the ZnO films with non‐metallic co‐dopants and their straightforward integration with molecular doping technology, which avoids several common drawbacks of ZnO electrodes. The observations show that optimized ZnO films with non‐metallic co‐dopants are a promising and competitive electrode for low‐cost and high performance organic solar cells and OLEDs.</P>