Influence of energy levels on the electronic properties of organic light harvesting devices

The charge carrier generation efficiency and the charge transfer rate at th e interface between charge carrier generation layer (CGL) and charge transp ort layer (CTL) were determined in dependence of the energy gap between the highest occupied molecule orbital (HOMO) levels. The bilayer photoreceptor s were characterized by the steady-state photoconduction method. The invest igated photoreceptors contained 4,4'-( (2,5-di-phenyl- 1,3,4-oxadiazol)-bis (azo)]-bis [3-hydroxy-(2H-benzimidazo(2,1-a]benz[d,e]isoquinolin-7-one)] as CGL. The energy gap between CGL and CTL was varied by employing seven diff erent triphenylenediamine derivatives (TPDs). The charge carrier generation efficiency and charge transfer rate measured were plotted against the ener gy gap. The result could be explained by the Marcus theory for energy gaps larger than 0.65 eV. (C) 2001 Elsevier Science B.V. All rights reserved.