High photovoltaic performance of ladder-type oligo-p-phenylene containing copolymers with high open-circuit voltages

The authors have designed and synthesized a serial of donor-accpter ladder-type oligo-p-phenylene containing copolymers, which were successfully used in high performance polymer heterojunction solar cells. Incorporation of ladder-type oligo-p-phenylenes, electron donating building blocks to the polymer backbone leads to an enhanced absorption band at 400 nm, as well as a low lying HOMO level, which results in an open-circuit voltage as high as 1.06 V, a more than 60 % increase compared to P3HT and many low band-gap polymers. The absorption range of this type of donor-acceptor copolymers can be further bathochromically tuned in order to well-match the solar spectrum by using a stronger acceptor. The results show that ladder-type oligo-p-phenylene containing polymers are promising candidates for achieving BHJ solar cells with high conversion efficiencies and high open circuit voltages.