Layer effects of photovoltaic heterojunction of fully conjugated heterocyclic aromatic rigid‐rod polymer poly‐p‐phenylenebenzobisoxazole

Poly-p-phenylenebenzobisoxazole (PBO) contains a fully conjugated rod-like backbone entailing excellent optoelectronic properties and superior stabilities. Poly(2,3-dihydrothieno-1,4-dioxin):polystyrenesulfonate (PEDOT:PSS) is a hole transferring medium, which was spun into a thin-film between PBO and indium-tin-oxide to facilitate photovoltaic (PV) effect by forming a donor-acceptor interlayer to separate and to transport photoinduced charges. Optimum PBO thickness for PV heterojunctions was about 71 nm at which the hole transferring PEDOT:PSS generated the maximum short circuit current (Isc) at a thickness of 115 nm. By using a layer of lithium fluoride (LiF) as an electron transferring layer adhering to Al cathode, the most open circuit voltage (Voc) and Isc were achieved with a LiF thickness of 1–2 nm because of possible electric dipole effect leading to an increase of Voc from 0.7 to 0.92 V and of Isc from about 0.1 to 0.2 μA. No PV response was observed for all PBO homojunctions because of insufficient exciton separation into electrons and holes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 988–993, 2007