Effect of Annealing Treatment and Surface Morphology on Power Conversion in Organic Photovoltaics

We investigated the effect of annealing treatment and surface morphology on power conversion efficiency (PCE) of organic photovoltaic (OPV) devices. The bulk-heterojunction OPV devices were fabricated by using poly(3-hexylthiophene) (P3HT) and phenyl-C-61-butyric acid methyl ester (PCBM) as a donor and an acceptor material, respectively. Significant changes of surface morphology and grain size were observed by varying annealing temperature, which is possibly due to different diffusion rate of PCBM molecules into the bulk-heterojunction polymer films. From these results, we conclude that differences in surface morphology and grain size are responsible for the significantly different PCE in the OPV devices. Consequently, the PCE is improved from 0.5 to 2.6% combined with the increase of short-circuit current and fill factor by annealing treatment at 150 degrees C. (C) 2009 The Japan Society of Applied Physics