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Spiro Structured Polyfluorene Derivatives with Solubilizing Alkyl Chains
Vak, Doojin,Shin, Se jin,Kim, Dong-Yu 한국공업화학회 2003 응용화학 Vol.7 No.2
Polyfluorenes with spiro structure chains were synthesized. Dinydroanthracene containing polyfluorene derivatives showed nearly the same optical properties as polydialkylfluorenes, however, the polymer exhibited greatly enhanced thermal properties followed by reduced harmful aggregate formation. The photoluminescence emission of the polymer film showed pure blue emission even after annealing at 200℃ for 15 hours in air. Electroluminescence spectrum also showed high color purity. Triphenylamine containing polyfluorene derivatives were also synthesized. The polymer showed enhanced thermal properties as well as increased HOMO energy level which could improve the hole injecting and transporting properties.
Jo, Jang,Vak, Doojin,Noh, Yong-Young,Kim, Seok-Soon,Lim, Bogyu,Kim, Dong-Yu Royal Society of Chemistry 2008 Journal of materials chemistry Vol.18 No.6
<P>This work proposes a new fluorene-based copolymer containing a spiroanthracenefluorene unit, poly[10,10-bis(2-ethylhexyl)-10<I>H</I>-spiro(anthracene-9,9′-fluorene)-2′,7′-diyl-co-bithiophene] (SFT2), for hole transporting materials in photovoltaic (PV) cells consisting of conjugated polymers and nanocrystalline TiO<SUB>2</SUB>. This polymer was synthesized to avoid photo- and thermo-oxidative degradation of poly[9,9′-dioctyl-fluorene-co-bithiophene] (F8T2) used in hybrid PV cells. The occurrence of oxidative degradation after irradiation with simulated sunlight or severe heating over the glass transition temperature in air on F8T2 and SFT2 films was confirmed by an increase of low energy emission at 600 nm in the photoluminescence emission spectra—originating from the generation of a keto defect site in the C-9 position of the fluorene units. In conclusion, we found that the defects play a vital role in degradation of the device performance of PV cells, especially in the decline of short-circuit current density (<I>J</I><SUB>sc</SUB>), consisting of fluorene-based polymers.</P> <P>Graphic Abstract</P><P>A new fluorene-based copolymer synthesized to avoid oxidative degradation was applied to a hybrid photovoltaic cell based on polymer/nanocrystalline TiO<SUB>2</SUB>, which showed stable performance for a long time in air. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b714138f'> </P>
Sequent Spray Deposition of Secondary Solvent for Efficient Polymer Solar Cells
유병관,김동유,Doojin Vak,조장,나석인,김석순,정은숙 한국고분자학회 2015 Macromolecular Research Vol.23 No.7
The spray process is compatible with the roll-to-roll process, which has the highest productivity and the lowest costs among the developed processing techniques. In this study, we demonstrated a technique involving the spraying of a secondary solvent after the formation of an active layer, by using a spray process with a relatively lowboiling- point solution. With this technique, we obtained the much smoother surface topography and more ordered bulk heterojunction morphology through enhanced self-organization of the composite materials. Consequently, the device with additionally sprayed high-boiling-point solvent allowed to achieve fill factor (FF) and power conversion efficiency (PCE) values as high as 67% and 3.76%, respectively.
Oh, Seung-Hwan,Vak, Doojin,Na, Seok-In,Lee, Tae-Woo,Kim, Dong-Yu WILEY-VCH Verlag 2008 Advanced Materials Vol.20 No.9
<B>Graphic Abstract</B> <P>A cationic water-soluble polyfluorene containing ion-transporting side groups and mobile metal ions is synthesized. The material is used as an electron injection layer in polymer light-emitting diodes with high-work-function Al cathodes. The devices show high quantum efficiencies (see figure), with a maximum external quantum efficiency of 4.8%, approaching the theoretical maximum external quantum efficiency of about 5%. <img src='wiley_img/09359648-2008-20-9-ADMA200702229-content.gif' alt='wiley_img/09359648-2008-20-9-ADMA200702229-content'> </P>
Factors to be Considered in Bulk Heterojunction Polymer Solar Cells Fabricated by the Spray Process
Byung-Kwan Yu,Doojin Vak,Jang Jo,Seok-In Na,Seok-Soon Kim,Mi-Kyoung Kim,Dong-Yu Kim IEEE 2010 IEEE journal of selected topics in quantum electro Vol.16 No.6
<P>One of the attractions of solution-processed polymer solar cells (PSCs) is the potential for low-cost production by high-throughput roll-to-roll processes. The spray process can be suggested as an elegant alternative for PSCs fabrication due to its high production speed. We highlight the effects of sprayed droplet sizes on the film topography and drying time of droplets. We relate the latter to the PSCs device performances. The transfer efficiency and deposition rate of the spray process as a function of the droplet size are investigated for the high production speed and lowering the cost. PSC device fabrication with an optimized spray-operating condition yielded a power conversion efficiency of 3.4%. The comparable efficiency of PSCs fabricated by a roll-to-roll compatible process compared to spin-coated one achieved in this paper brings these devices one step closer to the realization of low-cost PSCs production.</P>
Synthesis of novel arylamine containing perfluorocyclobutane and its electrochromic properties
Lim, Bogyu,Nah, Yoon-Chae,Hwang, Jin-Taek,Ghim, Jieun,Vak, Doojin,Yun, Jin-Mun,Kim, Dong-Yu Royal Society of Chemistry 2009 Journal of materials chemistry Vol.19 No.16
<P>A new electrochromic oligomer based on an arylamine compound containing a perfluorocyclobutane (PFCB) ring has been synthesized <I>via</I> 2 + 2 cyclodimerization. A new N,N,N′,N′-tetraphenyl-biphenyl-4,4′-diamine (TPD) with PFCB (<B>TPD-PFCB</B>) showed high thermal stability with a decomposition temperature (T<SUB>d</SUB>) of 435 °C. Cyclic voltammograms of <B>TPD-PFCB</B> films coated onto an indium–tin oxide substrate showed two reversible redox steps during a potential scan between 0.7 and 1.2 V. The spectroelectrochemical series of <B>TPD-PFCB</B> films exhibited color change from colorless to yellow and then to greenish blue during the oxidation reaction of <B>TPD-PFCB</B>. This oligomer exhibited a high electrochromic coloration efficiency (602 cm<SUP>2</SUP>/C) and a comparable response speed (coloring and bleaching time at 700 nm were 0.71 and 0.12 s, respectively).</P> <P>Graphic Abstract</P><P>A new electrochromic oligomer based on an arylamine compound containing a PFCB ring has been synthesized <I>via</I> 2 + 2 cyclodimerization and its electrochromic properties investigated. The oligomer exhibited a high electrochromic coloration efficiency and a comparable response speed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b817303f'> </P>
Oh, Seung-Hwan,Na, Seok-In,Jo, Jang,Lim, Bogyu,Vak, Doojin,Kim, Dong-Yu WILEY-VCH Verlag 2010 Advanced Functional Materials Vol.20 No.12
<P>Novel poly[(9,9-bis((6′-(N,N,N-trimethylammonium)hexyl)-2,7-fluorene)-alt-(9,9-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-9-fluorene)) dibromide (WPF-6-oxy-F) and poly[(9,9-bis((6′-(N,N,N-trimethylammonium)hexyl)-2,7-fluorene)-alt-(9,9-bis(2-(2-methoxyethoxy)ethyl)-fluorene)] dibromide (WPF-oxy-F) compounds are developed and the use of these water-soluble polymers as an interfacial layer for low-cost poly(3-hexylthiophene):phenyl-C<SUB>61</SUB> butyric acid methyl ester (P3HT:PCBM) organic solar cells (OSCs) is investigated. When WPF-oxy-F or WPF-6-oxy-F is simply inserted between the active layer and the cathode as an interfacial dipole layer by spin-coating water-soluble polyfluorenes, the open-circuit voltage (V<SUB>oc</SUB>), fill factor (FF), and power-conversion efficiency (PCE) of photovoltaic cells with high work-function metal cathodes, such as Al, Ag, Au, and Cu, dramatically increases. For example, when WPF-6-oxy-F is used with Al, Ag, Au, or Cu, regardless of the work-function of the metal cathode, the V<SUB>oc</SUB> is 0.64, 0.64, 0.58, and 0.63 V, respectively, approaching the original value of the P3HT:PCBM system because of the formation of large interfacial dipoles through a reduction of the metal work-function. In particular, introducing WPF-6-oxy-F into a low-cost Cu cathode dramatically enhanced the device efficiency from 0.8% to 3.36%.</P> <B>Graphic Abstract</B> <P>Copper as a cathode for organic solar cells! Thanks to novel water-soluble polyfluorene derivatives that are used as an interfacial dipole layer, low-cost and high-efficiency OSCs with high work-function metal cathodes are created. The efficiency of these OSCs is dramatically enhanced because of the formation of an interfacial dipole. In particular, for a copper cathode the device efficiency can be enhanced from 0.8% to 3.36%. <img src='wiley_img_2010/1616301X-2010-20-12-ADFM200902386-content.gif' alt='wiley_img_2010/1616301X-2010-20-12-ADFM200902386-content'> </P>