Origin of Charge Transfer Exciton Dissociation in Organic Solar Cells

Using a temperature (T)-dependent tight-binding (TB) model for an electron-hole pair at the donor-acceptor (DA) interface, we investigate the dissociation of charge transfer exciton (CTE) into free carriers, that is, an electron and a hole. We observe the existence of the localization-delocalization transition at a critical T, below which the charges are localized to the DA interface, and above which the charges are delocalized over the system. This explains the CTE dissociation observed in organic solar cells. The present study highlights the combined effect of finite T and carrier delocalization in the CTE dissociation

Electron-capture decay rate of ⁷Be encapsulated in a C₇₀ fullerene cage

The decay rate of ⁷Be electron capture in C₇₀ and Be metal was measured employing a reference method. The half-life (T_{1/2}) of ⁷Be endohedral C₇₀ (⁷Be@C₇₀) was found to be T_{1/2} = 52.49±0.04 d at room temperature (T = 293 K) and T_{1/2} = 52.42±0.04 d at liquid helium temperature (T = 5 K). Furthermore, the T_{1/2} of ⁷Be in Be metal was T_{1/2} = 53.25±0.04 d at room temperature (T = 293 K) and T_{1/2} = 53.39±0.03 d at liquid helium temperature (T = 5 K). These values for ⁷Be@C₇₀ at T = 5 K are approximately 1.6%(1.8%) smaller than those for ⁷Be in Be metal at T = 293 K (T = 5 K), indicating the difference in the electron wave functions for ⁷Be inside C₇₀ and ⁷Be in C60 and Be metal. The average charge transfer from the L(2s) electrons of the ⁷Be atom influences such variations in the decay constant (λ = ln2/T_{1/2}) in the environment. The experimental and theoretical investigations revealed that the change in the EC-decay rate of ⁷Be could be largely related to the potential configurations and the environment inside C60 and/or C₇₀ cages. The motion of ⁷Be inside cages was found to be restricted according to temperature

Ab-initio Molecular Dynamics Simulation of Li Insertion in C_<60>

Complexes composed of fullerenes and metal elements offer important examples as new nanomaterials in the field of materials design. In the collisions between C^-_ and Li^+ in plasma state, there is a possibility that the endohederal fullerene, Li@C_ is created as well as Li@C_ and so on. To study this phenomenon theoretically, we perform an all-electron mixed basis ab initio molecular dynamics simulation at 1, 000K which was developed by ourselves. When Li^+ with the kinetic energy ～5eV hits the center of a six-membered ring of C^-_, an endohedral complex, Li@C_ is created. This direcet insertion process is possible because the ionic radius of Li^+ is shorter then the radius of a six-membered ring. However, if either the kinetic energy is lower or the collision occurs off-center, the Li^+ ion stays outside and C_ is deformed by the shock