Mode Coupling Approach for spin-facilitated kinetic Ising models

The d-dimensional n-spin facilitated kinetic Ising model is studied analytically starting from usual master equations and their transformation into a Fock-space representation. The evolution of relevant operators is rewritten in terms of a projection formalism. The obtained frequency matrices and memory terms are analyzed. Especially, the influences of the memory terms is approached by using standard techniques of the usual mode coupling approach. The temperature dependence of the relaxation times related to the n-spin facilitated kinetic Ising model shows a weak non-Arrhenius behavior. Furthermore, a characteristic stretched decay of the correlation function is obtained.Comment: Written in REVTex, 18 pages, 7 figures in Postscrip

Multiple State Representation Scheme for Organic Bulk Heterojunction Solar Cells: A Novel Analysis Perspective

The physics of organic bulk heterojunction solar cells is studied within a six state model, which is used to analyze the factors that affect current-voltage characteristics, power-voltage properties and efficiency, and their dependence on nonradiative losses, reorganization of the nuclear environment, and environmental polarization. Both environmental reorganization and polarity is explicitly taken into account by incorporating Marcus heterogeneous and homogeneous electron transfer rates. The environmental polarity is found to have a nonnegligible influence both on the stationary current and on the overall solar cell performance. For our organic bulk heterojunction solar cell operating under steady-state open circuit condition, we also find that the open circuit voltage logarithmically decreases with increasing nonradiative electron-hole recombination processes.Comment: 6 pages, 4 figure

Capture numbers and islands size distributions in models of submonolayer surface growth

The capture numbers entering the rate equations (RE) for submonolayer film growth are determined from extensive kinetic Monte Carlo (KMC) simulations for simple representative growth models yielding point, compact, and fractal island morphologies. The full dependence of the capture numbers on island size, and on both the coverage and the D/F ratio between the adatom diffusion coefficient D and deposition rate F is determined. Based on this information, the RE are solved to give the RE island size distribution (RE-ISD). The RE-ISDs are shown to agree well with the corresponding KMC-ISDs for all island morphologies. For compact morphologies, however, this agreement is only present for coverages smaller than about 5% due to a significantly increased coalescence rate compared to fractal morphologies. As found earlier, the scaled KMC-ISDs as a function of scaled island size approach, for fixed coverage, a limiting curve for D/F going to infinity. Our findings provide evidence that the limiting curve is independent of the coverage for point islands, while the results for compact and fractal island morphologies indicate a dependence on the coverage.Comment: 13 pages, 12 figure