Effective mobility and photocurrent in carbon nanotube-polymer composite photovoltaic cells

We examine the dark and the illuminated current - voltage ( J - V) characteristics of poly( 3- octylthiophene) ( P3OT)/ single- wall carbon nanotube ( SWNT) composite photovoltaic cells as a function of SWNT concentration. Using an exponential band tail model, the influence of SWNT concentration on the J - V characteristics of the cells is analysed in terms of corresponding parameters such as effective hole mobility, short- circuit current, and open- circuit voltage. For the device with optimum 1% SWNT concentration, the increased photoresponse (similar to 500 times) as compared to the pristine P3OT cell can be attributed partly to the increase (similar to 50 times) in effective hole mobility, due to the reduction of localized states of the pristine P3OT matrix, and partly to the enhanced exciton extraction at the polymer/ nanotube junctions.