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Variable band gap conjugated polymers for optoelectronic and redox applications

Kim, Young Gi and Thompson, Barry C and Ananthakrishnan, Nisha and Padmanaban, G and Ramakrishnan, S and Reynolds, John R (2005) Variable band gap conjugated polymers for optoelectronic and redox applications. In: Journal of Materials Research, 20 (12). pp. 3188-3198.

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We report here on the utilization of variable band gap conjugated polymers for optoelectronic redox applications comprising organic photovoltaics, color tunable light emitting diodes, and electrochromics. For the evaluation of morphology in photovoltaic devices, atomic force microscopy, and optical microscopy provided direct visualization of the blend film structure. The evolution of the morphology in two and three component blends incorporating poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenlenevinylene] (MEH-PPV), poly(methylmethacrylate) (PMMA), and [6, 6]-phenyl C-61-butyric acid methyl ester (PCBM) was investigated. It was found that while insulating PMMA can be used to modulate the phase separation in these blends, a bicontinuous network of donor and acceptor was required to achieve the best device results. Similarity, a MEH-PPV copolymer with a decreased conjugation length has been used for investigating inter- and intramolecular photoinduced charge transfer in the presence of PMMA and PCBM. We fabricated MEH-PPV/PCBM solar cells that have power conversion efficiencies up to 1.5% with a range of 0.7-1.5%, dependent on the nature of the MEH-PPV used. This further indicates that in addition to blend morphology, polymer structure is critical for optimizing device performance. To this end, the concept of an ideal donor for photovoltaic devices based on poly[2,5-di(3,7-dialkoxy)-cyanoterephthalylidene] is described and two donor-acceptor polymers based on cyanovinylene (CNV) and dioxythiophene are discussed as representative examples of soluble narrow band gap polymers synthesized in our group. For light emitting applications, utilization of two blue emitting conjugated polymers poly (9,9-dioctylfluorene) (PFO) and poly[(9,9-dihexylfluorenyl-2,7-diyl)-co-(9,ethyl-3,6-carbazole)] (PFH-PEtCz) is presented for a color tunable polymer light emitting diode that emits orange, green, and blue light with a voltage range of 7-10 V as a function of the total conjugated polymer content in PMMA and is attributed to the phase separation between the conjugated polymers. Finally, the narrow band gap conjugated polymer, poly [bis(3,4-propylenedioxythiophene-dihexyl)]-cyanovinylene has been characterized for its electrochromic properties, illustrating the multifunctional nature of variable band gap conjugated polymers.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Materials Research Society.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Depositing User: Hemanth Rao K.R.
Date Deposited: 06 Feb 2010 08:31
Last Modified: 19 Sep 2010 04:57
URI: http://eprints.iisc.ac.in/id/eprint/17437

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