Infrared photocurrent spectral response from plastic solar cell with low-band-gap polyfluorene and fullerene derivative

Plastic solar cells were fabricated using a low-band-gap alternating copolymer of fluorene and a donor–acceptor–donor moiety (APFO-Green1), blended with [6,6]-phenyl-${\mathrm{C}}_{61}$ -butyric acid methylester or $3^{\prime }$ -(3,5-Bis-trifluoromethylphenyl)-$1^{\prime }$ -(4-nitrophenyl)pyrazolino[60]fullerene as electron acceptors. The polymer shows optical absorption in two wavelength ranges from $300<\lambda <500\mathrm{nm}$ and $650<\lambda <1000\mathrm{nm}$ . Devices based on APFO-Green1 blended with the later fullerene exhibit an outstanding photovoltaic behavior at the infrared range, where the external quantum efficiency is as high as 8.4% at $840\mathrm{nm}$ and 7% at $900\mathrm{nm}$ , while the onset of photogeneration is found at $1\mu \mathrm{m}$ . A photocurrent density of $1.76\mathrm{mA}∕{\mathrm{cm}}^2$ , open-circuit voltage of $0.54\mathrm{V}$ , and power conversion efficiency of 0.3% are achieved under the illumination of AM1.5 $(1000\mathrm{W}∕{\mathrm{m}}^2)$ from a solar simulator.