Charge injection rates in hybrid nanosilicon–polythiophene bulk heterojunction solar cells

The injection time for transfer of an electron from photoexcited dodecathiophene or polythiophene to a silicon nanocrystal (2.2 nm diameter) is calculated by computing the retarded Green’s function for the system from the Hamiltonian and Kohn–Sham states produced by density functional calculations. We found that it can be of the order of 10–100 fs if the thiophene chain lies approximately parallel to the silicon surface. However, the electron injection time is 1–2 orders of magnitude longer if the oligothiophene chain lies perpendicular to the silicon surface. A chemisorption interaction between the thiophene chain and the nanocrystal provides a relatively small improvement (decrease) of injection times, much weaker than that achieved by enforcing the parallel arrangement of the chain with respect to the nanocrystal

The influence of mixing on the stratospheric age of air changes in the 21st century

Climate models consistently predict an acceleration of the Brewer-Dobson circulation (BDC) due to climate change in the 21st century. However, the strength of this acceleration varies considerably among individual models, which constitutes a notable source of uncertainty for future climate projections. To shed more light upon the magnitude of this uncertainty and on its causes, we analyse the stratospheric mean age of air (AoA) of 10 climate projection simulations from the Chemistry-Climate Model Initiative phase 1 (CCMI-I), covering the period between 1960 and 2100. In agreement with previous multi-model studies, we find a large model spread in the magnitude of the AoA trend over the simulation period. Differences between future and past AoA are found to be predominantly due to differences in mixing (reduced aging by mixing and recirculation) rather than differences in residual mean transport. We furthermore analyse the mixing efficiency, a measure of the relative strength of mixing for given residual mean transport, which was previously hypothesised to be a model constant. Here, the mixing efficiency is found to vary not only across models, but also over time in all models. Changes in mixing efficiency are shown to be closely related to changes in AoA and quantified to roughly contribute 10 % to the long-term AoA decrease over the 21st century. Additionally, mixing efficiency variations are shown to considerably enhance model spread in AoA changes. To understand these mixing efficiency variations, we also present a consistent dynamical framework based on diffusive closure, which highlights the role of basic state potential vorticity gradients in controlling mixing efficiency and therefore aging by mixing

Transport properties of orbitally hybridized organic semiconductors

A microscopic theory based on the orbital hybridization model via single orbital approximation is developed to calculate the current variation in organic semiconductors that are coupled to the external orbits from the environment. The charge transfer resulted from the orbital hybridization between the environment and the organic semiconductor rebuilds the energy levels and eventually alters the transport properties of the organic semiconductor. Two parameters in our theory, the orbital energy level of the environment relative to the energy level of organic semiconductor and the orbital hybridization interaction, dominate the current variation in the organic semiconductors. Our results show that the suppression of atomic dimerization due to orbital hybridization gives rise to an increase of electrical conduction in organic semiconductor. Also, after coupling with the environment, the charge-donating organic semiconductors are more conductive than the charge-accepting ones