Polyfluorenes copolymers

M Svensson, F Zhang, SC Veenstra, WJH Verhees, JC Hummelen, JM Kroon, O Inganas, and MR Andersson, High-performance polymer solar cells of an alternating polyfluorene copolymer and a fullerene derivative, Adv. Mater., 15 988-991, 2003. 

M.J. Banach, R.H. Friend, and H. Sirringhaus, Influence of the casting solvent on the thermotropic alignment of thin liquid crystalline polyfluorene copolymer films, Macromolecules, 37 6079-6085, 2004. 

A.J. Campbell, D.D.C. Bradley, H. Antoniadis, M. Inbasekaran, W.W. Wu, and A.P. Woo, Transient and steady-state space-charge-limited currents in polyfluorene copolymer diode structures with ohmic hole injection contacts, Appl. Phys. Lett., 76 1734-1736, 2000. 

Dias FB, King S, Monkman AP, Perepichka n, Kryuchkov MA, Perepichka IF, Bryce MR (2008) Dipolar stabilization of emissive singlet charge transfer excited states in polyfluorene copolymers. J Phys Chem B 112 6557-66... 

Despite the success of the disorder model concerning the interpretation of data on the temperature and field dependence of the mobility, one has to recognize that the temperature regime available for data analysis is quite restricted. Therefore it is often difficult to decide if a In p vs or rather a In p vs representation is more appropriate. This ambiguity is an inherent conceptual problem because in organic semiconductors there is, inevitably, a superposition of disorder and polaron effects whose mutual contributions depend on the kind of material. A few representative studies may suffice to illustrate the intricacies involved when analyzing experimental results. They deal with polyfluorene copolymers, arylamine-containing polyfluorene copolymers, and c-bonded polysilanes. 

Fig. 8 Temperature dependence of the zero field hole mobility in the low carrier density limit in a polyfluorene copolymer. The data are inferred from space-charge-limited current experiments and analyzed in terms of the extended Gaussian disorder model (see Sect. 4.1). From [90] with permission. Copyright (2008) by the American Institute of Physics...

In fact, in their recent work, Mensfoort et al. [90] conclude that in polyfluorene copolymers hole transport is entirely dominated by disorder. This is supported by a strictly linear In p cx dependence covering a dynamic range of 15 decades with a temperature range from 150 to 315 K (Fig. 8). Based upon stationary space-charge-limited current measurement, where the charge carriers are in quasi equilibrium so that dispersion effects are absent, the authors determine a width a of the DOS for holes as large as 130 meV with negligible polaron contribution. 

Khan RUA, Poplavskyy D, Kreouzis T, Bradley DDC (2007) Hole mobility within arylamine-containing polyfluorene copolymers a time-of-flight transient-photocurrent study. Phys Rev B 75 035215... 

Loi MA, Toffanin S, Muccini M, Forster M, Scherf U, Scharber M (2007) Charge transfer excitons in bulk heterojunctions of a polyfluorene copolymer and a fullerene derivative. Adv Funct Mater 17 2111... 

Veldman D, Ipek O, Meskers SCJ, Sweelssen J, Koetse MM, Veenstra SC, Kroon JM, van Bavel SS, Loos J, Janssen RAJ (2008) Compositional and electric field dependence of the dissociation of charge transfer excitons in alternating polyfluorene copolymer/fullerene blends. J Am Chem Soc 130 7721... 

FIGURE 10.27. Current-voltage-luminance characteristics of polyfluorene copolymer LEDs using (a) green and (b) red emitters, (c) EL spectra of the respective LEDs. (From Ref. 6.)... 

Yohannes T, Zhang F, Svensson M, Hummelen JC, Andersson MR, Ingantls O (2004) Polyfluorene copolymer based bulk heterojunction solar cells. Thin Solid Films 449 152... 

The photophysics of jt-conjugated polymers are reviewed in detail in other chapters of this book. (See, for example, Chapter 3.) Here, we focus on the electronic and photophysical phenomena that occur at the heterojunction between two different semiconductor polymers. The heteroj unctions are formed by combining four different polyfluorene copolymers in blend or bilayer thin films and are investigated using time-resolved and steady-state, temperature- and elec-tric-field-dependent photoluminescence measurements as well as electroluminescence and time-resolved spectroscopy. We review a body of work carried out in our laboratories over the last few years, and published in numerous journal articles (see refs. [13-17]). 

In Section 2.1.4, the electronic and photophysical properties of donor-acceptor or type-II heterojunctions between two semiconductor polymers were investigated. Exciplex formation was found to be a general phenomenon for type-II heterojunctions between polyfluorene copolymers. These are among the most widely used materials in polymer optoelectronics, but the presence of exciplexes had not yet been fully appreciated. This is because the exciplex population is often depopulated via efficient endothermic transfer towards the exciton, which leads to bulk exciton instead of exciplex emission. However, via time- and temperature-depen-dent photoluminescence (PL) spectroscopy the exciplex states can be identified. Employing a relationship known from small-molecule solution systems that relates the relative HOMO and LUMO levels of the molecules to the exciplex emis-... 

The Suzuki coupling is particularly powerful, since the polymer properties can be easily tuned by varying the structure of the monomers, and indeed a large number of different polyfluorene copolymers have been made in this way [54]. 

K.G. Jespersen, F.L. Zhang, A. Gadisa, V. Sundstrom, A. Yartsev, and O. Inganas, Charge formation and transport in bulk-heterojunction solar cells based on alternating polyfluorene copolymers blended with fuUerenes, Org. Electr., 7, 235-242 (2006). 

M.-H. Chen, J. Hou, Z. Hong, G. Yang, S. Sista, L.-M. Chen, Y. Yang, Efficient Polymer Solar Cells with Thin Active Layers Based on Alternating Polyfluorene Copolymer/Fullerene Bulk Heterojunctions. Adv. Mater. 2009, 21,4238-4242. 

P Wang, A. Abrusci, H. M. P. Wong, M. Svensson, M. R. Andersson, N. C. Greenham, Photoinduced Charge Transfer and Efficient Solar Energy Conversion in a Blend of a Red Polyfluorene Copolymer with CdSe Nanoparticles. Nano Letters 2006,6,1789-1793. 

P. Wang, et al., Photoinduced charge transfer and efficient solar energy conversion in a blend of a red polyfluorene copolymer with CdSe nanoparticles. Nano Letters, 2006. 6(8) p. 1789-1793. 

Yang NC, Lee SM, Yoo YM, Kim JK, Suh DH. New blue electroluminescent n-type polyfluorene copolymers with a 1,3,4-oxadiazole unit in the main chain. J Polym Sci Part A Polym Chem 2004 42(5) 1058-68. 

Jespersen, K.G. et al. (2004) The electronic states of polyfluorene copolymers with alternating donor-acceptor units./. Chem. Phys., 121 (24), 12613-12617. 

Zhang, F.L. etal, (2006) Influence of solvent mixing on the morphology and performance of solar cells based on polyfluorene copolymer/flillerene blends. Adv. Funct. Mater., 16 (5),... 

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