Peng Q, Park K, Lin T, Durstock M, Dai L. Donor-pi-acceptor conjugated copolymers for photovoltaic applications: tuning the open-circuit voltage by adjusting the donor/acceptor ratio. J Phys Chem B. 2008 Mar 13;112(10):2801–8. doi: 10.1021/jp7105428. PMID: 18281978.