A green neutral state donor-acceptor copolymer for organic solar cells

We report on the photophysical and photovoltaic properties of a low band gap polymer bearing a quinoxaline moiety, poly(2,3-bis(3,4-bis(decyloxy)phenyl)- 5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)quinoxaline) PDOPEQ, as an electron donor in bulk heterojunction solar cells blended with the acceptor 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM). Devices were composed of PDOPEQ and varying amounts of PCBM (1:1, 1:2, 1:3, 1:4 w-w ratio). The components were spun cast from chlorobenzene (CB) and characterized by measuring current-voltage characteristics under simulated AM 1.5 conditions. The devices with 1:3 polymer to PCBM ratio exhibited short circuit current density (Jsc) of 0.8 mA cm^-2, an open circuit voltage (Voc) of 0.2 V, and a fill factor (FF) of 0.3. Incident photon to current efficiency (IPCE) is also reported. The IPCE spectrum spans from 400 nm to 800 nm and exhibits a photocurrent contribution of ca. 5.5% at around 400 nm. The nanoscale morphology was investigated with atomic force microscopy (AFM). Photoinduced absorption spectroscopy confirms the photoinduced charge transfer in such donor acceptor blends.