Improved morphology of polymer-fullerene photovoltaic devices with thermally induced concentration gradients

Gradient concentration profiles for efficient charge transfer and transport can be created in polymer-fullerene organic photovoltaics by thermally induced interdiffusion of an initial bilayer. Prior demonstrations with poly[2-methoxy-5-(2(')-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and C-60 have been limited by the low miscibility of the two component materials. The morphology of the interdiffused films and resultant photovoltaic efficiency are improved by the use of the more miscible electron donor/electron acceptor pair of poly(3-octylthiophene) and C-60. The resultant concentration gradient profile is demonstrated by Auger spectroscopy and ion-beam milling. Increases in the short-circuit currents and fill factors relative to interdiffused MEH-PPV/C-60 devices lead to monochromatic power conversion efficiencies of 1.5% at 470 nm. (C) 2005 American Institute of Physics.