Excitonic cell

In order to demonstrate the NDCPA a model of a system of excitons strongly coupled to phonons in a crystal with one molecule per unit cell is chosen. This model is called here the molecular crystal model. The Hamiltonian of... 

To verify effectiveness of NDCPA we carried out the calculations of absorption spectra for a system of excitons locally and linearly coupled to Einstein phonons at zero temperature in cubic crystal with one molecule per unit cell (probably the simplest model of exciton-phonon system of organic crystals). Absorption spectrum is defined as an imaginary part of one-exciton Green s function taken at zero value of exciton momentum vector... 

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). 

New Solar Cells Quantum Dot (QD) Structures and Multiple Exciton Generation (MEG)... 

The second type of solar cell is based on a /m-heterojunction in analogy to semiconductor devices [274]. Excitons generated by light, diffuse and dissociate at the interface between a hole and an electron-conducting material. The optimum layer thickness was calculated to be 1.5 times the exciton diffusion length [275]. 

Fig. 4 Schematic illustration of the processes leading to photocurrent generation in organic solar cells, (a) Photon absorption in Step 1 leads to excitons that may diffuse in Step 2 to the donor/ acceptor (D/A) interface. Quenching of the exciton at the D/A interface in Step 3 leads to formation of the charge-transfer (CT) state. Note that processes analogous to Steps 1-3 may also occur in the acceptor material, (b) Charge separation in Step 4 leads to free polarons that are transported through the organic layers and collected at the electrodes in Steps 5 and 6, respectively, (c) The equilibria involved in Steps 1-4- strongly influence device efficiency...

Gregg BA (2003) Excitonic solar cells. J Phys Chem B 107 4688... 

Stubinger T, Bruiting W (2001) Exciton diffusion and optical interference in organic donor-acceptor photovoltaic cells. J Appl Phys 90 3632... 

Luhman WA, Holmes RJ (2009) Enhanced exciton diffusion in an organic photovoltaic cell by energy transfer using a phosphorescent sensitizer. Appl Phys Lett 94 153304... 

Lee J, Vandewal K, Yost SR, Bahlke ME, Goris L, Baldo MA, Manca JV, Van Voorhis T (2010) Charge transfer state versus hot exciton dissociation in polymer-fullerene blended solar cells. J Am Chem Soc 132 11878... 

Defects with large central cell correction have very localized wave functions. The larger the correction, the more localized the wave function and the higher the probability of interaction between the core (or central cell) and the electron and/or the exciton bound to the defect. Hence the reason why the line is so much smaller than the Q line in the spectrum, as well as the reason why the phonon replicas to the Q-line, is simply a matter of probability, since the central cell correction is so much larger for a nitrogen defect on a cubic site than a hexagonal site. 

Huffman, D. R., L. A. Schwalbe, and D. Schiferl, 1982. Use of smoke samples in diamond-anvil cells to measure pressure dependence of optical spectra application to the ZnO exciton, Solid State Commun. (in press). 

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