Charge transfer networks

The use of interpenetrating donor-acceptor heterojunctions, such as PPVs/C60 composites, polymer/CdS composites, and interpenetrating polymer networks, substantially improves photoconductivity, and thus the quantum efficiency, of polymer-based photo-voltaics. In these devices, an exciton is photogenerated in the active material, diffuses toward the donor-acceptor interface, and dissociates via charge transfer across the interface. The internal electric field set up by the difference between the electrode energy levels, along with the donor-acceptor morphology, controls the quantum efficiency of the PV cell (Fig. 51). 

A very interesting approach is the combination of charge-transfer donor-acceptor sites in one molecule as it was demonstrated for compounds consisting of oligophenylenevinylene and C o moieties [281, 282]. By microphase separation, a bicontinous network is formed for the charge transport. The efficiencies are, however, quite low (0.01-0.03%). 

Figure 10. Resistor-network representation of porous-electrode theory. The total current density, i, flows through the electrolyte phase (2) and the solid phase (1) at each respective end. Between, the current is apportioned on the basis of the resistances in each phase and the charge-transfer resistances. The charge-transfer resistances can be nonlinear because they are based on kinetic expressions.

The first step in the deposition process is that in which an ion crosses the electrified interface, i.e., the charge-transfer reaction. Picture the situation (Fig. 7.122). A hydrated ion (e.g., a silver ion) is waiting at the OHP. In the direction of the silver metal electrode, there is the three-dimensional network, or lattice, consisting of silver ions cemented together by an electron gas. The silver ions in the lattice each lay claim to an electron of the electron gas in this sense, they can be said to be neutral and... 

Figure 1 A distributed resistor network models approximately how the apphed potential is distributed across a DSSC under steady-state conditions. For various values of the interparticle resistance, fiT,o2, and the interfacial charge transfer resistance, Rc the voltage is calculated for each node of the Ti02 network, labeled Vj through V . This is purely an electrical model that does not take mobile electrolytes into account and, therefore, potentials at the nodes are electrical potentials, whereas in a DSSC, all internal potentials are electrochemical in nature.

It is possible to solve this model analytically. The model is useful for calculating the qualitative potential distribution in high-surface-area solar cells and how it is influenced by the relative facility of different charge-transfer pathways. Solutions for a 100-resistor network are shown in Fig. 2, where Vapp = 1.0 V, Rs = 0.001 11, and RTi02 + Rct = 104fl. 

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