Charge Generation and Transport in Polymers

Id is the ionization potential of the excited state of the polymer (donor). As is the electron affinity of the sensitizer molecule, and Uc denotes the Goulomb attraction between the separated radicals. Polarizability of the surrounding matrix, morphology of the polymer which introduces a large separation between the donor and the acceptor, or a potential barrier preventing the separation of the electron-hole pair are factors that may inhibit an energetically allowed GT process (8,9). 

For electron-acceptor-type GG molecules, the electron density on the ring system is low due to the presence of strong electron-withdrawing groups such as -NO2 and -CN. The chemical structures of selected electron acceptors viz. 

Other methods of sensitization include the use of semiconductor quantum dots (CdS or CdSe) or functionalizing the polymer with sensitizing moieties such as transition metal complexes [13]. For example, the studies performed by covalently attaching the ruthenium (Ru) complex Ru(bpy)2(m-COOH-4-methylbpy)(PF(5)2 to PVK using Friedel-Crafts acylation showed that the photogeneration efficiency of 

The role of the sensitizer is vital in the formation of the space charge field, but the concentration of the sensitizer cannot be increased with an intention to increase 

Another type of charge-transporting polymers has the transport unit covalently attached to the polymer main chain. This reduces the passive volume of the host as the polymer itself takes part in the charge-transport process. PVK, first synthesized in 1934 by the polymerization NVK, is the first-known polymer photoconductor with relatively stable radical cations and high charge-carrier mobility [26]. Polymerization of NVK can be carried out by cationic, free-radical, CT, coordination, or electrochemical process [27, 28]. 

---