Abstract
We investigated the effect of cooling rate in the annealing treatment of bulk heterojunction organic photovoltaic devices using blend films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the active layer. Slow cooling after thermal annealing altered the surface morphology and optical properties of the film as compared with those of fast cooling, which resulted in higher power conversion efficiency (PCE). The incident photon-to-current conversion efficiency (IPCE) was also improved in the case of slow cooling. The highest PCE, 3.4% under air mass 1.5 simulated solar illumination (100 mW/cm2), was achieved.