Chromophore Design for Photorefractive Organic Materials

Würthner, Frank; Wortmann, Rüdiger; Meerholz, Klaus

doi:10.1002/1439-7641(20020118)3:1<17::aid-cphc17>3.0.co;2-n

Cited by 222 publications

(140 citation statements)

References 91 publications

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“…Additionally, the above-mentioned experimental values were not obtained from solar-cell-like structures but from sub-monolayer samples, 47 from solutions in toluene, 51 and from the gas phase. 50 Taking into account that not only the molecular structure 52 but also the polarity of the molecules' surroundings influences the polarizability, 53 the agreement between the experimental values and the estimate based on our fit parameters was rather good.…”

Section: A Influence Of the Cell Thicknesssupporting

confidence: 55%

Field-dependent exciton dissociation in organic heterojunction solar cells

et al. 2012

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In organic heterojunction solar cells, the generation of free charge carriers takes place in a multistep process which involves charge transfer (CT) states, that is, bound electron-hole pairs at the interface between donor and acceptor molecules. Past efforts to model the CT-state dissociation during solar cell operation were not able to consistently reproduce the experimentally observed field and temperature dependence. This discrepancy between model and experiment was partly due to the field-dependent free charge carrier collection process, which plays an important role in the widely used bulk heterojunction cell configuration and superimposes a possible field-dependent charge carrier generation process. In order to distinguish between generation and collection of free charge carriers, we propose the planar heterojunction cell configuration as a model system to study the field-dependent charge carrier generation process in organic heterojunction solar cells. We apply this model system to check current CT-state dissociation models against experimental data. Although the models can quantitatively account for the photocurrent's dependence on the applied voltage and the device thickness, they fail to account for the virtually negligible temperature dependence of the field-dependent charge-generation process. This discrepancy is traced back to a common feature of the models: an Arrhenius-like temperature dependence, distinctive of all processes involving a thermally activated jump over an energy barrier. As a solution to the problem, we introduce an exciton dissociation model based on a field-dependent tunnel process and demonstrate its consistency with the experimental observations. Our results indicate that the current microscopic picture of the charge-generation process in organic heterojunction solar cells being limited by the CT-state dissociation process needs to be reconsidered.

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Section: A Influence Of the Cell Thicknesssupporting

confidence: 55%

Field-dependent exciton dissociation in organic heterojunction solar cells

et al. 2012

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“…[49][50][51] It was confirmed experimentally that the external field stabilizes the highly Resonance Raman intensity analysis was conducted for 17 and 18 as monomers in dichloromethane solutions and as H-dimers in dioxane solutions. [51][52][53] Dyes 19 have large dipole moments in the ground and excited states, showing considerable contributions of structures A and C. 51 It was concluded that the resonance Raman excitation profiles and the basic features of the optical absorption spectra of H-dimers may be well explained by a simple molecular exciton model, which assumes that the two monomers interact through coupling between their transition dipole moments; the excitonically coupled monomer model is not adequate here (Scheme 8).…”

Section: Dimeric and Polymeric Cyaninesmentioning

confidence: 79%

Cyanines Bearing Quaternary Azaaromatic Moieties

2007

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“…86 Polarizability anisotropy Δα, the ground-state dipole moment μ and the first hyperpolarizability β are significantly affected by structural modifications due to changes in the electron-donating and -accepting substituent groups. The two terms of FOM of the NLO chromophores with various π-conjugated structures with different electron-donating and -accepting substituent groups were individually evaluated as a function of the resonance parameter c 2 for two basic resonance states of push-pull chromophores, a neutral polyene limit (D-A, c 2 = 0), cyanine limit with c 2 = 0.5, zwitterionic limit (betaine type, D + -A − , c 2 = 1) 26,86,87 and as a function of π-bond-order alternations (BOAs). 27,88,89 For π-conjugated molecules with single-double bond series, bondlength alternation (BLA) is defined in terms of the difference between the average lengths of single bonds and that of double bonds, which is significantly related to the optimized geometries.…”

Section: Nlo Dyesmentioning

confidence: 99%

“…The same types of plots were reported by Würthner's group. 86,87 Kippelen et al 88 also plotted the two terms of FOM and FOM as a function of BOA. The product of μβ was shown to have two extrema with a positive maximum (at 0oc 2 o0.5, − 0.65oBOAo0), a negative maximum (at 0.5oc 2 o1, 0oBOAo0.65) and zero at the cyanine limit (c 2 = 0.5, BOA = 0).…”

Section: Nlo Dyesmentioning

confidence: 99%

“…Namely, the contribution of the hyperpolarizability term due to the electro-optic effect (Pockels effect) was far outweighed by the contribution of the linear polarization term due to the birefringence of the NLO molecule by the space-charge field (molecular orientation enhancement). 26,27,[86][87][88][89] Beyond the cyanine limit (c 2 40.5, BOA40), some problems have been noted: 26,87 high-melting crystalline solids are generated, which lead to difficulties of dissolving the materials in rather non-polar polymeric matrices. Then, the molecular design around cyanine limits offers better NLO chromophores for enhanced PR performance.…”

Section: Nlo Dyesmentioning

confidence: 99%

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Molecular design of photorefractive polymers

Tsutsumi

2016

Polym J

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This review article describes the current state-of-the-art research on organic photorefractive polymer composites. A historical background on photorefractive materials is first introduced and is followed by a discussion on the opto-physical aspects and the mechanism of photorefractivity. The molecular design of photorefractive polymers and organic compounds is discussed, followed by a discussion on optical applications of the photorefractive polymers. Polymer Journal (2016) 48, 571-588; doi:10.1038/pj.2015.131; published online 27 January 2016 BACKGROUND In this report, the molecular design of organic photorefractive (PR) polymers is reviewed. Organic PR polymers are materials that possess both electro-optical and photoconductive properties. Research on photoconductive polymers, whose pioneering polymer is poly(N-vinyl carbazole) (PVK, PVCz), began in the 1960s. From the 1980s, research on organic nonlinear optical (NLO) materials has been widely conducted in the fields of organic electro-optics and optical nonlinearity. From the 1990s, new technology using organic photorefractivity combined with photoconductive and electro-optical properties was introduced in the field of organic semiconducting materials, 1 and organic light-emitting diodes 2-6 and organic fieldeffect transistors 7 were also debuted in this field. At the same time, the interest of researchers also turned toward the development of organic photovoltaic cells and organic solar cells. [8][9][10][11] The transport of charge carriers through photoconductive manifolds is a common phenomenon found in PR, organic light-emitting diode or organic photovoltaic materials. Thus, the development of materials in each field is expected to merge together to trigger the development of novel materials.The PR effect is a well-known phenomenon that is observed in materials in which refractive index modulation is induced by the space-charge field that results from the redistribution of positive and negative charge carriers separated through photo-excitation. 12 This phenomenon was first reported in inorganic crystals of lithium niobate (LiNbO 3 ) and lithium tantalate (LiTaO 3 ) and was observed through heterogeneous optically induced refractive indices in 1966. 13 Since then, the PR effect has extensively been investigated in many inorganic crystals, and theoretical approaches have been established to explain this phenomenon. 14 In 1991, 1 the first study of PR polymers reported a low diffraction efficiency of 10 −3 to 1% and a small optical gain of 0.33 cm À1 . In 1994, 15 a high diffraction efficiency of 86% (the remaining 14% was attributed to optical losses) and a large optical gain exceeding 200 cm À1 was reported in photoconductive PVK-based PR composites. Over the past two decades, many featured review articles [16][17][18][19][20][21][22][23][24][25][26][27] and book

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Chromophore Design for Photorefractive Organic Materials

Cited by 222 publications

References 91 publications

Field-dependent exciton dissociation in organic heterojunction solar cells

Field-dependent exciton dissociation in organic heterojunction solar cells

Cyanines Bearing Quaternary Azaaromatic Moieties

Molecular design of photorefractive polymers

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