Conduction properties of carbon nanotubes in P3HT:SWNT bulk heterojunction solar cells

An improved understanding of photovoltaic and electrical properties of poly-3(hexylthiophene) (P3HT) - single walled carbon nanotubes (SWNT) bulk heterojunction solar cells was achieved by studying light and dark characteristics current density and voltage (J-V) characteristics of devices fabricated with different blend ratios. The SWNTs inside P3HT were found to be in the form of ropes of diameters up to 30 nm. The open circuit voltage (Voc) of the solar cell to observed to reduce - from 0.45 V to 0.017 V - with increase in SWNT concentration - from 0 wt% to 2 wt%. The Fill Factor (FF) and short circuit current density (Jsc) were found to be fairly constant at around 2 μA cm⁻². The comparative analysis of the dark J-V characteristics of the devices characterised helped isolate the current density components JSWNT and JP3HT, due to SWNT and P3HT respectively. Electron affinity values of 3.13 eV and 3.58 eV were calculated for P3HT and SWNTs.