Polymer Solar Cells Based on a Low‐Bandgap Fluorene Copolymer and a Fullerene Derivative with Photocurrent Extended to 850 nm

Polymer solar cells have been fabricated from a recently synthesized low band‐gap alternating polyfluorene copolymer, APFO‐Green2, combined with 6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) from organic solutions. External quantum efficiencies (EQEs) of the solar cells show an onset at 850 nm and a peak of > 10 % located at 650 nm, which corresponds to the extended absorption spectrum of the polymer. Photocurrent of 3.0 mA cm^–2, photovoltage of 0.78 V, and power conversion efficiency of 0.9 % have been achieved in solar cells based on this new low‐bandgap polymer under the illumination of air mass 1.5 (AM 1.5) (1000 W m^–2) from a solar simulator.