Flexible thin film solar cells based on a pentacene/${\mathrm{C}}_{60}$ heterojunction on indium tin oxide coated polyethylene terephthalate (PET) substrates are described. Devices grown on PET are compared to those on glass substrates. The nature of the organic grains grown on PET and glass substrates is shown to have a significant impact on the device short circuit current. Device performance under mechanical strain and elevated temperature is reported. Devices deliver an $8.8\mathrm{mA}{\mathrm{cm}}^{-2}$ short circuit current density with a 1.6% power conversion efficiency under an AM1.5 simulated solar intensity of $80\mathrm{mW}{\mathrm{cm}}^{-2}$ . The relatively low $300\mathrm{mV}$ open circuit voltage appears to limit device efficiency.

We report the observation of a spin-dependent dark transport current, exhibiting spin coherence at room temperature, in a $\pi${}-conjugated polymer-fullerene blend using pulsed electrically detected magnetic resonance. The resonance at g=2.0028(3) is due to polarons in the polymer, and exhibits spin locking at high microwave fields. The presence of an excess of fullerene, and the operating voltage (1~V) used, suppresses negative polaron formation in the polymer. It is concluded that spin-dependent transport is due to the formation of positive bipolarons.

We report fabrication of a $\mathrm{Ti}{\mathrm{O}}_2$ interconnected network structure for photovoltaic applications, which was obtained using polystyrene-block-polyethylene oxide diblock copolymer as the templating agent. The synthetic method is simple and highly reproducible. The pore size of the structure is controlled by the amount of Ti precursor provided. The heterojunction solar cells consisting of a $\mathrm{Ti}{\mathrm{O}}_2$ porous network structure and poly (2-methoxy-5-($2^{\prime }$ -ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) showed improved performance with a short circuit current of $3.25\mathrm{mA}∕{\mathrm{cm}}^2$ under AM 1.5 solar illumination. The achieved maximum external quantum efficiency for optimum MEH-PPV thickness was 34%.