In this work, intensity sensitive organic photodiodes were made based on the drop-on-demand piezoelectric inkjet printing of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blend on the ITO substrates. Inkjet conditions for printing the P3HT:PCBM/chlorobenzene solution were studied and the influences of concentration and inkjet parameters such as pulse voltage and the method of stacking spots were systematically investigated under the goal of optimizing the morphology and uniformity of P3HT:PCBM spots on various kinds of ITO substrates. P3HT:PCBM films in any shape and size were prepared by overlapping the neighboring spots and bulk heterojunctions were fabricated after the deposition of a thin Al film as cathode on their top. Under the excitation of a 532 nm pulse laser source, the open-circuit voltage (Voc) between the ITO and Al electrodes could be detected. Intensity sensitive photo-diodes were obtained with a quantum yield of similar to 0.35% and the time constant was estimated to be similar to 1.0 mu s. Ways for further improvement on the performance of the photo-diodes were also suggested.