Low band-gap polymeric photovoltaic devices

We present results on photovoltaic devices based on novel thiophene-isothianaphthene copolymers (PDTI) with pi-pi* band-gaps ranging from 1.2 eV to 1.8 eV. Single-layer photovoltaic devices were fabricated from films of PDTI doped with a soluble fullerene derivative [6,6]-phenyl-C-61-butyric-acid-methyl-ester (PCBM) as the electron acceptor and blended into poly(methyl methacrylate) to enhance the film quality. These devices exhibit spectral response extending into the infrared and are better matched to the solar spectrum as compared to standard PPV based ones. Such low band-gap materials also make possible the construction of dye-sensitized photovoltaic devices that take advantage of energy transfer from high energy absorbing dyes to the host polymer.