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 (∼500 times) as compared to the pristine P3OT cell can be attributed partly to the increase (∼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.