The performance of poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) organic photovoltaic (OPV) devices was found to be strongly influenced by environmental during preparation, thermal annealing conditions, and the material blend composition. We optimized laboratory fabricated for these variables. Humidity fabrication process can cause electrode oxidation photo-oxidatio...