Vera Cimrova

Improvement in carrier mobility and photovoltaic performance through random distribution of segments of linear and branched side chains

The random distribution of segments of linear octyloxy side chains and of branched 2-ethylhexyloxy side chains, on the backbone of anthracene containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene) (PPE-PPV) has resulted in a side chain based statistical copolymer, denoted AnE-PVstat, showing optimized features as compared to the well defined homologues whose constitutional units are incorporated into its backbone. Electric field independent charge carrier mobility (µhole) for AnE-PVstat was demonstrated by CELIV and OFET measurements, both methods resulting in similar µhole values of up to 5.43 × 10−4 cm2 V−1 s−1. Upon comparison, our results show that charge carrier mobility as measured by CELIV technique is predominantly an intrachain process and less an interchain one, which is in line with past photoconductivity results from PPE-PPV based materials. The present side chain distribution favors efficient solar cell active layer phase separation. As a result, a smaller amount of PC60BM is needed to achieve relatively high energy conversion efficiencies above 3%. The efficiency of ηAM1.5 ≈ 3.8% obtained for AnE-PVstat:PC60BM blend is presently the state-of-art value for PPV-based materials.

π‐Conjugated Donor and Donor–Acceptor Metallo‐Polymers

Two zinc(II)- and two ruthenium(II) containing π-conjugated metallo-polymers were synthesized and characterized in detail. We could prove by SEC, analytical ultracentrifugation (AUC) and viscosimetry the ruthenium(II) metallo-polymers to be high molar mass materials (M(fs) u2009=u200920u2009000u2009gu2009·u2009mol(-1) Ru1-2; M(fs) u2009=u200934u2009000u2009gu2009·u2009mol(-1) Ru1) exhibiting intrinsic viscosities of up to [η]u2009=u2009192u2009·u2009cm(3) u2009·u2009g(-1) . Applying spin-coating we produced homogeneous films of the polymers and could, subsequently, investigate the photophysical properties in the solid state. Introducing the Ru(II) metallo-polymers mixed with PCBM[60] as photoactive layer in bulk-heterojunction solar cells resulted in very low efficiencies due to morphology problems.

Comparison of the birefringence in an azobenzene-side-chain copolymer induced by pulsed and continuous-wave irradiation

A comparative study of photoinduced birefringence in azobenzene-side-chain copolymers under continuous-wave (cw) and pulsed irradiation is presented. Absolute refractive index changes were determined by the attenuated total reflection spectroscopy. We clearly demonstrated that pulsed, similarly to cw, irradiation induces a three-dimensional reorientation of azobenzene chromophores. For the same light dose, pulsed irradiation using ns pulses of appropriate pulse energy led to higher values of birefringence, which can be attributed to a cooperative motion of azobenzene side chains and thermal effects induced by the laser pulses.

Tuning the properties of an anthracene-based PPE-PPV copolymer by fine variation of its macromolecular parameters

The effects of a moderate variation of the molecular weight on the optical, structural, morphological and transport properties of an anthracene-containing PPE-PPV copolymer are investigated, as well as their overall implication on the photovoltaic parameters of bulk-heterojunction solar cells. Just a two-fold variation in the molecular weight is enough to induce appreciable changes in the properties of the investigated polymer films, indicating that a fine tuning of the macromolecular parameters is required for the optimization of the properties of polydispersed molecular systems. A remarkable role of the polydispersity index in the organization of polymer chains, thus reflecting in the electronic properties of the polymer films, is observed.

Electroluminescence in Polymeric Systems with Defined Chemical and Morphological Structure

Recent advances in the design and fabrication of polymeric light emitting diodes are discussed with respect to the major physical processes governing the generation of light from charge carrier recombination. Emphasis is put on charge injection, photoluminescence efficiency, color tuning, control of polarization and microcavity effects. The results show, that the macroscopic device parameters are closely related to the chemical structure of the conjugated polymer backbone as well as the morphology and the geometry of the emission layer.