Studies on the influence of four different solvents on the morphology and photovoltaic performance of bulk‐heterojunction films made of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM) via spin‐coating for photovoltaic applications are reported. Solvent‐dependent PCBM cluster formation and P3HT crystallization during thermal annealing are investigated with optical microscopy and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) and are found to be insufficient to explain the differences in device performance. A combination of atomic force microscopy (AFM), X‐ray reflectivity (XRR), and grazing‐incidence small‐angle X‐ray scattering (GISAXS) investigations results in detailed knowledge of the inner film morphology of P3HT:PCBM films. Vertical and lateral phase separation occurs during spin‐coating and annealing, depending on the solvent used. The findings are summarized in schematics and compared with the IV characteristics. The main influence on the photovoltaic performance arises from the vertical material composition and the existence of lateral phase separation fitting to the exciton diffusion length. Absorption and photoluminescence measurements complement the structural analysis.

Light-scattering spectra of the glasses polystyrene ͑PS͒, polycarbonate ͑PC͒, and Ca 0.4 K 0.6 (NO 3 ) 1.4 ͑CKN͒ are measured in the frequency interval 3Ϫ10000 GHz covering a broad temperature range. The low frequency wing of the fast relaxation spectrum is found to show a power-law behavior with an exponent ␣ϭ0.2Ϫ0.6. The exponent depends on system and temperature. No indication of a crossover to a white noise spectrum, as previously reported and discussed within mode-coupling analyses is found. It is shown that the Gilroy-Phillips model of thermally activated transitions in asymmetric double-well potentials well describes the power-law part of fast relaxation spectra in PS and CKN but fails in the case of PC. The distribution of barrier heights is extracted from the spectra. ͓S0163-1829͑98͒04645-1͔

We present depolarized light scattering data of the glass former toluene as obtained from tandem Fabry–Perot interferometry and Raman scattering covering a frequency range 0.5 GHz<v<5000 GHz. A large temperature interval of the (supercooled) liquid (Tg=117 K<T<295 K) as well as of the glass (7 K<T<117 K) is measured. Testing the scaling laws of idealized mode coupling theory (MCT) we find that MCT provides a satisfying interpolation up to the fluid regime (T/Tg=2.5) and a critical temperature Tc≅153 K is extracted. Deviations from the high-temperature MCT laws below Tc can be identified by constructing a master curve for the α-process. The deviations are attributed to spectral contributions from the high-frequency wing of the α-process and/or of the slow β-process which appear apparently only below Tc. A comparison with dielectric spectroscopy data, exhibiting a strong β-process, confirms this. Furthermore, we carry out a phenomenological analysis which assumes additivity of the susceptibility of α-process and fast dynamics. This approach allows us to single out the fast dynamics spectrum and to determine the nonergodicity parameter f. Whereas 1−f(T) is essentially constant above 160 K, a sharp decrease is observed below 160 K. This decrease stops at T=Tg and only a weak temperature dependence survives below Tg. Thus, the fast dynamics changes its characteristics at Tc and Tg. We speculate on the possibility of an ideal glass state exhibiting no relaxation any longer, and finally we comment on reasons for the large scatter of Tc data reported for some glass formers so far.

We investigated the glass former triphenyl phosphite by calorimetry, Brillouin scattering, and dielectric and nuclear magnetic resonance spectroscopy. Time-resolved experiments demonstrate the conversion between three distinctly different phases, namely, the supercooled liquid, a recently discovered apparently amorphous phase (glacial phase), and the crystalline phase. The temperature dependencies of the properties provided by the different methods are compared. We find significant molecular motion in the glacial phase. From this we hypothesize that the glacial phase is a different highly viscous liquid or a solid phase with some kind of cooperative relaxation.

Precise low-frequency light scattering experiments on silica glass are presented, covering a broad temperature and frequency range ( 9 GHz

Molecular reorientation in the two amorphous phases of triphenyl phosphite, namely the supercooled liquid (phase aI) and the newly discovered second amorphous phase (phase aII), was investigated by dielectric relaxation and by two-dimensional (2D) nuclear magnetic resonance spectroscopy (NMR) in the time and frequency domain. Whereas phase aI exhibits the relaxational features typical of supercooled liquids, the molecular motion in phase aII is characterized by an extremely broad dielectric loss and by a pronounced nonexponential reorientational correlation function. Using a Gaussian distribution of correlation times, both dielectric and NMR data reveal consistently correlation times on the order of seconds. The quantitative analysis of the 2D spectra favors the interpretation that molecular motion in phase aII leads to an isotropic distribution of molecular orientation on the surface of a sphere. In addition, we find a secondary relaxation process that shows basically the same features in both phases. We conclude that the newly discovered phase is a second liquid phase with a very unusual reorientational correlation function. However, a nematic liquid crystal cannot completely be ruled out.

We present dielectric relaxation (DS) and light scattering (LS) data of several glass formers. Relaxational features are compiled which are not yet properly taken into account by current models. (i) We distinguish two types of glass formers. Type A systems do not show a slow -process whereas type B systems do. A full line-shape analysis of is presented . In type A systems the evolution of the high-frequency wing of the -process is the most prominent spectral change while cooling and leads to an essentially constant loss at . The analysis of of type B systems is carried out within the Williams-Watts approach and we focus on the temperature dependence of the -relaxation strength. (ii) Concerning fast relaxations below as revealed by LS we identify relaxation with a low-frequency power-law behaviour. No indication of a crossover to a white noise spectrum as previously reported and discussed within MCT is found. Analysing this relaxation we recourse to the model of thermally activated transitions in asymmetric double well potentials. We show that the model works well in some cases and the distribution of barrier heights may be extracted, but in other systems pronounced deviations occur.

We present quasielastic light scattering and dielectric spectra of the glass former alpha-picoline. At high temperatures the evolution of the susceptibility minimum is well described by the mode coupling theory (MCT). Below the critical temperature T(c) the simple scaling laws of MCT fail due to the appearance of the excess wing of the alpha process, which shows a universal evolution as a function of log(10)tau(alpha). Taking this into account, however, we observe the predicted cusplike anomaly of the nonergodicity parameter as well as a crossover to "white noise."