MATERIALS AND METHODS

3.4.1 CELL CONSTRUCTION

The enriched CNSCs (figure 1) consist of a transparent glass slide covered with an enriched mixture of 90% semiconducting and 10% metallic nano­tubes (IsoNanotubes-S 90% Powder, Nano Integris Inc.). These nanotubes have a diameter of 1.2-1.7 nm and a length of 0.1-4 m. Below this is a silicone insulator with a hole filled with electrolyte (iodide-triiodide, So – laronix). The electrolyte is in contact with both carbon nanotube films and acts to reduce the photo-active side as well as close the electrical circuit at the counter electrode. At the bottom is a glass slide covered with a regular mixture of 2/3 semiconducting and 1/3 metallic nanotubes that acts as a coun­ter electrode (Unidym, lot PO-325, formerly Carbon Nanotechnologies Inc.). These nanotubes have a diameter of 0.8-1.2 nm and a length of100-1000 nm. Dispersion of carbon nanotubes were made by ultrasonic agitation in 1,2-di – chloroethane for 1 h for the regular mixture and 4 h for the enriched mixture. The dispersion was spray painted with an air brush onto glass substrates in a vented cylindrical enclosure. The slides were rotated while spraying to obtain uniform coverage. Subsequently, the glass slides were heated on a hot plate to evaporate any residual solvent. The resulting film is similar to the well-known bucky paper and it has metallic properties [38]-[40]. The final solar cell has an exposed surface area of ~4.8 mm2 with a distance of ~2.5 mm between the electrodes. The glass slides are 1 mm thick and did not have a conducting coating prior to carbon nanotube application.