Poly(3-hexylthiophene) (P3HT) is used as a conjugated polymer material for the fabrication of organic solar cells. To enhance the performance of the solar cell, it is crucial to improve the charge transport properties of the out-of-plane direction, which corresponds to the direction normal to the cell. The out-of-plane hole mobility in P3HT films before and after rubbing was investigated. The mobility was measured by the time-offlight method and was enhanced by a factor of 8 with rubbing. The enhancement of mobility is significantly dependent on the regioregularity (RR) of P3HT and is the largest with low RR (91%). The mobility of low RR becomes almost equal to that of high RR (98%) after rubbing. Polarized absorption and Raman spectral measurements, and optical, atomic force, and scanning electron microscopy observations indicate the mobility enhancement can be attributed to aggregation and molecular planarity enhanced by rubbing. Three enhancement factors (EFs) for the mobility, aggregation, and planarity were quantified by changing the RR. It was thus determined that subtle aggregation produces a large mobility enhancement. According to the results of grazingincidence X-ray diffraction measurement, the increase of face-on component of P3HT by rubbing was observed and corresponds to the increase of π−π staking of thiophene ring along the out-of-plane direction. Evolution from the disordered to the ordered P3HT structure by rubbing significantly improves hole transport in the out-of-plane direction.

A hybrid solar cell composed of a crystalline semiconductor and polymer film has attracted much attention due to numerous advantages, such as high mobility, long lifetime, and the aqueous solution processing. Recently, the power conversion efficiency (PCE) of the hybrid solar cell of silicon (Si) wafer and poly­(3,4-ethylenedioxythiophene)-poly­(styrenesulfonate) (PEDOT:PSS) is reported to be higher than that of a commercial amorphous Si solar cell. Here in the Si/PEDOT:PSS hybrid solar cell was prepared using dimethyl sulfoxide (DMSO) as an additive to the PEDOT:PSS solution. The PCE was increased up to 10-fold by the addition of DMSO at a concentration of 5 wt%. Results from grazing-incidence X-ray diffraction, atomic force microscopy, and Raman spectroscopy indicated the 10-fold enhancement was controlled by the nanostructure of the PEDOT:PSS film. The enhanced performance was attributed to (i) an increase of π–π stacking, (ii) shortened distances between π–π planes, (iii) an increase in the quinoid structure of PEDOT, and (iv) reduced PEDOT:PSS particle size. The PCE was also enhanced by a transparent cathode of colloidal Ag nanowires and through the use of a vacuum-free process for preparation of the PEDOT:PSS film.

A time evolution of polar molecules inhomogeneously dispersing in mesoscale is investigated by dynamic light scattering around the gas-liquid critical point. The dynamics evaluated on phase diagrams produces a contour map of critical slowing down and suggests a ridge to be a trace of intermediate lines between gas and liquid states. A good coincidence between dynamics and static inhomogeneities is confirmed in the wide density, and it is consistent with theoretical expressions.

White-light-emitting silicon nanocrystals (Si-NCs) ranging from the near UV to the red region were fabricated by pulsed laser ablation (PLA) of a bulk silicon crystal in a supercritical fluid. The broad photoluminescence (PL) spectra, white light continuum, were investigated by measuring time evolution against aging in the atmosphere or oxygen ambience. The results show that the PL intensity of the higher-energy component increases, whereas that of the lower-energy component decreases as aging time increases. According to rate constants of PL intensity enhancement, the increase in the PL intensity was ascribed to the oxidation of the Si-NCs. This enhancement became significant when the sample was generated at the thermodynamic state, showing a critical anomaly of supercritical CO2. That is, rapid cooling of the hot Si-NC in supercritical CO2 immediately after PLA produces a luminescent Si-NC in the blue-green wavelength region. On the basis of PL spectral measurements at five excitation wavelengths, the lower- and higher-energy PL components were assigned to electronic structures arising from the quantum confinement effect of the Si-NC and the electron–hole recombination at the radiative centers at the surface of the Si-NC, respectively.

Vibrational Raman spectra of the C horizontal lineC stretching modes of cis- and trans-1,2-dichloroethylene (C(2)H(2)Cl(2)) were measured in supercritical carbon dioxide (CO(2)). The spectra were collected at a fixed solute mole fraction by varying the fluid density by a factor of 20. As the density increased, the peak frequencies of the C horizontal lineC stretching modes shifted toward the low-energy side at isotherms of reduced temperature, T(r) = T/T(c) = 1.02, 1.06, and 1.20. By analyzing these density dependences using the perturbed hard-sphere theory, we decomposed the shifts into attractive and repulsive components. The repulsive shifts of cis-C(2)H(2)Cl(2) were almost equivalent to those of trans-C(2)H(2)Cl(2). However, the attractive shifts of nonpolar trans-C(2)H(2)Cl(2) were significantly greater than those of polar cis-C(2)H(2)Cl(2) at all densities and temperatures. To evaluate the difference in the isomers, we calculated the attractive shifts of the C horizontal lineC stretching modes of each isomer, composing of dispersion, dipole-induced-dipole, and dipole-quadrupole interactions between solute C(2)H(2)Cl(2) and solvent CO(2) molecules. These three interactions were quantified by considering molecular configurations and orientations, and solvation structures around the isomers were elucidated by 3D schematic diagrams. As a result, it was shown that the anisotropic solvation structure around trans-C(2)H(2)Cl(2) was responsible for the larger attractive shifts in the supercritical CO(2). The difference of solvation structures between the isomers was significant at T(r) = 1.02 but became minor as the temperature increased to T(r) = 1.20.