Abstract
Due to the small dielectric constant of pristine conjugated polymers or small molecules, the photogenerated electron-hole pairs (excitons) are strongly bound because of Coulombic attraction, typically 0.2–0.5 eV (Brédas et al., 1996; Alvarado et al., 1998; and Arkhipov and Bässler, 2004) and are unable to dissociate automatically. The most effective way to solve the issue is to introduce another component possessing electron affinity into the photo-active film. The intermixing of electron donor (D) and electron acceptor (A) materials form the type II heterojunctions, where both highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the electron donor are higher than the electron acceptor. In particular, new interfacial electronic states between donor and acceptor are formed, called charge transfer (CT) states, where interesting optoelectronic processes, such as charge separation and recombination, take place (Benson-Smith et al., 2007).
Published Version
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