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

Abstract Polymer solar cells have been fabricated from a recently synthesized low band‐gap alternating polyfluorene copolymer, APFO‐Green2, combined with 6,6‐phenyl‐C 61 ‐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.