Post-fabrication annealing effects in polymer-nanotube photovoltaic cells

We present a systematic study of the effects of post-fabrication annealing on the performance of photovoltaic devices that incorporate a photoactive donor-acceptor dispersed heterojunction system. Solar cells have been fabricated based on poly(3-octylthiophene) as donor (D) and single-wall carbon nanotubes as the electron acceptor (A) with a PEDOT:PSS hole transport layer. A post-fabrication annealing treatment was carried out at a temperature range of 40-200 degrees C. The best results were obtained at 120 degrees C; at this temperature the cell shows a short circuit current, I-sc = 0.5 mA cm(-2), an open circuit voltage, V-oc = 0.75 V and a fill factor, FF = 0.6, resulting in a power conversion efficiency of eta = 0.22% under AM 1.5 (100 mW cm(-2)) white light illumination. The annealing treatment led to a doubling of the power conversion efficiency. This was attributed to a better charge carrier transport in the polymer matrix and more effective charge separation and collection.