The polarization energies of 44 organic solids were determined by ultraviolet photoelectron spectroscopy in the gaseous and solid states. Condensed polycyclic aromatic hydrocarbons with planar molecular structures were found to have a common value, 1.7 eV, independent of their molecular sizes and also their crystal structures. The common value is approximately interpreted by the first-order expression for the polarization energy. A large variation of values in the range 0.9-3.0 eV was obtained for several compounds. Among them, molecules with intricate structures have smaller values and those with large molecular polarizabilities have larger values than the common value. These results indicate that the polarization energy of an organic solid is mainly determined by two factors: the molecular polarizability and the molecular packing in the solid. Intermolecular interactions in the solid, other than the van der Waals force, also contribute to the value.

Thermoelectric harvesting of waste heat offers great opportunities for energy production. Here, we demonstrated that a minor Cu addition in the n-type Mg 3 Sb 1.5 Bi 0.5 realized the remarkable enhancement of low-temperature thermoelectric performance. Coupled with p-type a-MgAgSb, we fabricated a high-performance thermoelectric module, which showed a record-high conversion efficiency of 7.3% at the hot-side temperature of 593 K. Our module rivals the longtime champion Bi 2 Te 3 in this applicably important temperature range, providing great promise for harvesting abundant low-grade waste heat.

The structure of the thin film phase of pentacene was investigated using x-ray diffraction reciprocal space mapping (RSM). The crystal structure was found to be triclinic with the following lattice parameters: a=0.593nm, b=0.756nm, c=1.565nm, α=98.6°, β=93.3°, and γ=89.8°. Atomic positions were determined by comparing the observed RSM diffraction intensities with theoretical calculations.

Influence of the direction of spontaneous orientation polarization on the charge injection properties of organic light-emitting diodes