307 publications from this institution
We describe two methods by which discotic liquid crystalline (LC) triphenylene materials can be sensitized for wavelengths of the visible spectrum and the near IR. One way of doping is more conventional and uses bi-layers between the LC-system and an adjacent pigment layer. The second doping is achieved by a molecular doping with C<sub>70</sub>. Here the influence of doping on the measured mobilities is much smaller as compared to the influence of doping measured in amorphous systems. We attribute this smaller influence of the C<sub>70</sub>-doping on the mobility to a partial phase separation occuring between the LC-host material and the C<sub>70</sub>-guest molecules. In our comparative experiments on doped dimethyl-triphenyldiamines we can show taht the magnitude of the trap depths for hole-trapping has a very large influence on the measured transport parameters.
The synthesis and analysis of solution processable polymers for organic solar cells is crucial for innovative solar cell technologies such as printing processes. In the field of donor materials for photovoltaic applications, polymers based on tetraphenylamine (TPA) are well known hole conducting materials. Here, we synthesized two conjugated TPA containing copolymers via Suzuki polycondensation. We investigated the tuning of the energy levels of the TPA based polymers by two different concepts. Firstly, we introduced an acceptor unit in the side chain. The main-chain of this copolymer was built from TPA units. The resulting copolymer 2-(4-((4'-((4-(2-ethylhexyloxy)phenyl)(paratolyl) amino)biphenyl-4-yl)(para-tolyl)amino)benzylidene) malononitrile P1 showed a broader absorption up to 550 nm. Secondly, we used a donor-acceptor concept by synthesizing a copolymer with alternating electron donating TPA and electron withdrawing Thieno[3,4-b]thiophene ester units. Consequently, the absorption maximum in the copolymer octyl-6-(4-((4-(2-ethylhexyloxy)phenyl)(p-tolyl)amino)phenyl)-4-methylthieno[3,4-b]thiophene-2-carboxylate P2 was red shifted to 580 nm. All three polymers showed high thermal stability. By UV-vis and Cyclic voltammetry measurements the optical and electrochemical properties of the polymers were analyzed.