Ladder-type oligo-p-phenylene containing donor-acceptor copolymers are disclosed. The ladder-type oligo-p-phenylene can be used as an electron donor unit in the disclosed copolymers to provide a deeper highest occupied molecular orbital (HOMO) level for obtaining polymeric solar cells having a higher open-circuit voltage. Particular electron-accepting units, e.g., a divalent fused-ring heterocyclic moiety selected from the group consisting of a substituted or unsubstituted benzothiadiazole, a substituted or unsubstituted quinoxaline, a substituted or unsubstituted benzobisthiazole, and a substituted or unsubstituted naphthothiadiazole, can be used to tune the electronic band gaps of the polymers for a better light harvesting ability. The disclosed copolymers exhibit field-effect mobilities as high as 0.011 cm.sup.2/(V s). Compared to fluorene-containing copolymers with the same acceptor unit, the disclosed ladder-type oligo-p-phenylene containing copolymers have enhanced and bathochromically shifted absorption bands and much better solubility in organic solvents.
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made in part with United States Government support under FA9550-06-1-0076 awarded by the Air Force Office of Scientific Research (AFOSR) and DE-FG01-07ER-46465 awarded by the Department of Energy (DOE). The U.S. Government has certain rights in the invention.