Polymer‐based photovoltaic devices have been fabricated by blending the conjugated polymer, poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV) with the buckminsterfullerene, C60. The photo‐induced current and the open‐circuit voltage show a strong dependence on the polymer processing conditions. It was found that the photovoltaic devices fabricated with tetrahydrofuran or chloroform (non‐aromatic solvents) have smaller photocurrents under same reverse bias as well as higher open circuit voltages than the devices fabricated with xylene, dichlorobenzene, or chlorobenzene (aromatic solvents). The device performance dependence on the processing solvent is attributed to the different solvation‐induced polymer morphology.

Articles you may be interested inMobility and metal-insulator transition of the two-dimensional electron gas in SiGe/Si/SiGe quantum wells

Magnetic reconnection is an important process in various collisionless plasma environments because it reconfigures the magnetic field and releases magnetic energy to accelerate charged particles. Its dynamics depend critically on the properties of the pre-reconnection current sheet. One property in particular, cross-sheet temperature inhomogeneity, which is ubiquitous throughout the heliosphere, has been shown to increase reconnection outflow speed, energy conversion efficiency, and secondary island formation rate using two-dimensional particle-in-cell simulations. Here we expand upon these findings, considering two cases with a long, thin current sheet, one with homogeneous temperature and one with inhomogeneous temperature across the current sheet. In the inhomogeneous temperature case, numerous secondary islands form continuously, which increases current sheet turbulence (well-developed cascade power spectra) at large wavenumbers. Current density, energy conversion, dissipation, and acceleration of high-energy particles are also enhanced relative to the homogenous temperature case. Our results suggest that inhomogeneous temperature profiles, which are realistic, need to be incorporated into studies of turbulence and particle acceleration in collisionless magnetic reconnection.

We have investigated the valley splitting of two-dimensional electrons in high quality Si/Si1−xGex heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor ν = 3 (∆3) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear density dependence of ∆3 on the electron density was observed, while the slope of these two configurations differs by more than a factor of two. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of ∆3 before and after the coincidence.