Excitons organic solar cells

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...

The photovoltaic effect in organic solar cells arises, not from formation of free charge carriers in one or both phases, as in a classical siliconp-n junction cell, but from exciton dissociation at the junction between the two phases. Photon absorption in organic semiconductors, whether small molecules or polymers, does not generate free holes and... 

We have given an overview of the recent works on nanocomposites used for optoelectronic devices. From the review it is seen that a very rich publication has been issued regarding the nanostructured composites and nano-hybrid layers or heterojunctions which can be applied for different practical purposes. Among them there are organic light emitting diodes (OLED) and excitonic or organic solar cells (OSC). 

After ionization of the excitons, the spatial separation of electrons and holes is small, i.e. <10 nm. Therefore, the charges attract each other by Coulomb interaction, and cannot be thought of as two independent freely moving species (Figure 13.2b). In the literature on organic solar cells this situation is described as bound electron-hole pairs , or geminate electron-hole pairs . The separation of electron and hole can be so small that their... 

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