Hyperbranched polythiophenes were synthesized by potentiodynamic electropolymerization of 2,2';3',2''-terthiophene and 5'-(2-thienyl)-2,2';3',2''-terthiophene. The molecular architecture, i.e., the extent of branching of the resulting polymers, could be adjusted by varying the switching potentials. We compare these systems to hyperbranched polythiophenes which we obtained via a simple one-pot synthesis route based on FeCl(3) oxidative polymerization of the monomers. Interestingly, we find that the properties of the electropolymerized materials obtained with high switching potentials are comparable to those of the chemically synthesized polythiophenes. A detailed optical and electrochemical characterization of these systems is performed showing the high potential of this material class for optoelectronic applications. Cyclic voltammetry coupled with in situ conductance measurements further reveal reversible doping upon oxidation (p-doping) and reduction (n-doping) and comparable values for the conductance for the chemically and electrochemically synthesized materials.

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.

We present the synthesis of regioregular polythiophenes with alkylthiophene side chains P3TC16 prepared by Ni-catalyzed polymerization from the branched, thiophene-based monomer 5-bromo-5″-hexadecyl-[2,2′;3′,2″]terthiophene. The optical properties in solution and thin films of the polymer were investigated in situ as a function of temperature and compared to the low regioregularity analogue FeP3TC6 synthesized by Fe(III) mediated oxidative polymerization of 5″-hexyl-[2,2′;3′,2″]terthiophene. It was found that due to the regioregular structure, P3TC16 tends to strong aggregation in solution, which is ascribed to π−π interactions. The bandgap in thin films of 1.88 eV is slightly smaller than the bandgap of the reference polymer poly(3-hexylthiophene) (P3HT, 1.91 eV). Interestingly, it was found that the HOMO and LUMO levels of P3TC16 are shifted to significantly lower values as compared to P3HT. First results regarding the application of P3TC16 in FETs are shown and mobilities of up to 3.1 × 10 −2 cm 2 /(V s) were achieved. Open circuit voltages of up to 710 mV in combination with PC[60]BM in organic solar cells were found, which is about 30% higher than for P3HT, which can be attributed to the low HOMO energy level.

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.