Remarkable charge-transfer mobility from [6] to [10]phenacene as a high performance p-type organic semiconductor

The relationship between structure and charge transport properties of phenacene organic semiconductors has been studied with focus on [6] -> [10] phenacene. Upon inserting phenyl rings, the p-extended structure results in strong electronic coupling interactions and reduction of reorganization energy. Using the classical Marcus charge transport theory, we predict that hole mobility in the phenacene series increases gradually up to 8.0 cm(2) V-1 s(-1) at [10] phenacene. This is remarkably high among other discovered OSCs, surpassing that of pentacene. Moreover, we notice that the experimental hole mobility of [6] phenacene is unusually low, inconsistent with other members in the same series. Thus, we performed full structural relaxation on phenacene and revealed similarities between theoretical and experimental crystal structures for all the members except [6] phenacene. We propose a new structure of [6] phenacene under the consideration of van der Waals force with smaller lattice parameters a* and b* compared to the experimental structure. Our new structural calculation fits well with the existing trend of hole mobility, energy gaps, effective masses, bandwidth and lattice parameters. Single-shot G(0)W(0) calculations are performed to verify our structures. The results give a hint that the improvement in [6] phenacene efficiency lies on the intermolecular distance along the stacking direction of the crystal. Phenacene compounds generally have small effective masses, high charge transfer integrals and moderate reorganization energies necessary for hole transport. Our results suggest that the phenacene series, in particular [6] -> [10]phenacene, have high charge mobility and air stability essential for achieving high efficiency electronic devices.11Ysciescopu

Electron-hole asymmetry in Co- and Mn-doped SrFe2As2

Phase diagram of electron and hole-doped SrFe2As2 single crystals is investigated using Co and Mn substitution at the Fe-sites. We found that the spin-density-wave state is suppressed by both dopants, but the superconducting phase appears only for Co (electron)-doping, not for Mn (hole)-doping. Absence of the superconductivity by Mn-doping is in sharp contrast to the hole-doped system with K-substitution at the Sr sites. Distinct structural change, in particular the increase of the Fe-As distance by Mn-doping is important to have a magnetic and semiconducting ground state as confirmed by first principles calculations. The absence of electron-hole symmetry in the Fe-site-doped SrFe2As2 suggests that the occurrence of high-Tc superconductivity is sensitive to the structural modification rather than the charge doping.Comment: 7 pages, 6 figure

Small anisotropy in iron-based superconductors induced by electron correlation

We have investigated the electron correlation effect on the electronic structures and transport properties of the iron-based superconductors using density functional theory (DFT) and dynamical mean field theory (DMFT). By considering the Fe 3d electron correlation using DMFT, the quasiparticle bandwidth near the Fermi level is found to be substantially suppressed compared to the conventional DFT calculation. Because of the different renormalization factors of each 3d orbital, DMFT gives considerably reduced electrical anisotropy compared to DFT results, which explains the unusually small anisotropic resistivity and superconducting property observed in the iron-based superconductors. We suggest that the electron correlation effect should be considered to explain the anisotropic transport properties of the general d/f valence electron system.close3