ABSTRACT
The potential of 2,2';3,2â³-terthiophene (3T) as branching units in 3D copolymers is presented with EDOT as an example comonomer. Branched EDOT/3T polythiophenes were prepared by electropolymerization, and their electrochemical and optical properties are discussed. Two different approaches were employed: (i) the direct electropolymerization of a novel branched thiophene monomer (3TE3) consisting of a 3T core that contains three outer EDOT end groups and (ii) the electrochemical copolymerization of a EDOT/3T mixture in different ratios from [1:1] to [1:10]. Cyclic voltammetric and vis spectrometric experiments show that the EDOT content within the polymer has a strong influence on the electronic properties of the material: with increasing EDOT content, the HOMO-LUMO gap is decreased. To prove copolymer formation of EDOT and 3T, chemically synthesized reference copolymers of EDOT and 3T were prepared by oxidative coupling using FeCl3, and their optical and electronic properties were compared to those of the electrodeposited films. In addition, the copolymer formation is indicated by the comparison of the electrochemical and spectroscopic results with those of the homopolymers P3T and PEDOT.
ABSTRACT
The synthesis of ionically functionalized branched polythiophenes with either carboxylic acid (anionic, P3T-COOH) or methylimidazolium (cationic, P3T-MIM) end groups is presented. Due to the large number of end groups present in the polymer, the functionalization has a major impact on the solubility of the polymers. In the case of P3T-COOH, the polymer shows a fully reversible phase transfer between organic solvents and water, depending on the pH. Remarkably, the ionic-liquid-modified polymer P3T-MIM is soluble in a room-temperature ionic liquid. The absorption properties are unaffected by the functional end groups.
ABSTRACT
Branched conjugated architectures should possess the advantage of isotropic charge transport compared to conventional linear conjugated polymers, as for example poly(3-hexylthiophene) (P3HT) which is commonly used in organic solar cells. This contribution investigates the optoelectronic properties of branched poly(thiophene)s p3T and p4T synthesized in a straightforward one-pot procedure by oxidative coupling of branched trithiophene and tetrathiophene monomers with FeCl(3). These polymers can be regarded as model systems for ideal amorphous conjugated materials. Optical characterization in solution and in thin films together with cyclic voltammetry data suggests the applicability of these materials for the use in organic solar cell devices. In particular, the HOMO and LUMO levels of the branched polythiophenes are shifted to lower energy values as compared to linear P3HT. Field effect mobilities are in the order of 10(-4) cm(2)/(V s). A first optimization of solar cell devices based on the branched polythiophene materials in combination with PCBM as acceptor resulted in efficiencies of 0.6% with open-circuit voltages being about 30% higher (up to 714 mV) than normally found with P3HT.
ABSTRACT
We report the simple one-pot synthesis of size tunable zinc oxide nanoparticles (ZnO NPs) out of an organometallic ZnO precursor using the self-assembly of solution phase polystyrene-block-poly(2-vinylpyridine) micelles. The resulting hybrid material could be deposited on various substrates in a straightforward manner with the NPs showing size-dependent absorption and photoluminescence due to the quantum-size effect. We compare the results to the assembly of preformed NPs which are selectively incorporated in the poly(2-vinylpyridine) core of the micelles due to the high affinity of ZnO to vinylpyridine.
ABSTRACT
Hyperbranched polythiophenes were prepared via a simple one-pot synthesis approach based on oxidative coupling of branched conjugated monomers. Only small variations in the building unit and architecture lead to large differences of absorption and photoluminescence properties. Interestingly, soluble hyperbranched polythiophenes with relatively small molecular weights show enhanced absorption at low and high wavelengths compared to linear analogues, such as poly(3-hexyl thiophenes) with high molecular weights. With this versatile approach we present a method to design tailor made, functional materials with potential applications in optoelectronics.
ABSTRACT
Highly dispersed ZnO nanoparticles with variable particle sizes were successfully prepared within an amphiphilic hyperbranched polyetherpolyol matrix via decomposition of an organometallic precursor in the presence of air leading to stable nanocomposites. The high degree of stabilization during and after the synthesis by the polymer permits control over the nanoparticle size and therefore, due to the quantum-size-effect, the particle properties. Furthermore, these polymer-inorganic nanocomposites can easily be dispersed in apolar solvents to yield highly transparent, stable solutions.
