A Comparative Study of Poly(3-octylthiophene) and Poly(3-hexylthiophene) Solar Cells Blended with Single Walled Carbon Nanotubes

Poly(3-hexylthiophene) (P3HT):single walled carbon nanotube (SWNT) and poly(3-octylthiophene) (P3OT):SWNT thin films and bulk heterojunction solar cells were fabricated with 0, 1, and 2 wt % of SWNTs. The current density in P3HT is found to be higher than that of P3OT by an order of magnitude at 5 V. Hole mobility in P3HT is found to be higher than in P3OT. Photoluminescence measurements show that the nature of electronic interaction of SWNTs with P3OT and P3HT is not same. For P3OT:SWNT (1 wt %) devices, a ∼3 times increase in the short circuit current density J sc was obtained compared to pristine P3OT device. For P3HT:SWNT devices, no such improvement was found. The open circuit voltage V oc of P3HT:SWNT (1 wt %) solar cell was found to be 0.82 V while 1.2 V was obtained for P3OT:SWNT (1 wt %) solar cell. This is higher than 0.98 V previously reported for similar solar cells. It is found that the V oc decreases with increase in SWNT content due to the SWNTs acting as shunt paths between anode and cathode.