ZnO nanorods grown on plastic substrates by chemical methods are combined with both inorganic and organic p-type materials to make flexible p-n junction devices. When bent the devices generate both voltage and current peaks, which is attributed to the piezoelectric effect in the ZnO nanorods. The best device produces a maximum possible power density of 100 nWcm‑2. When vibrated at a constant frequency the voltage output by the devices scales linearly with vibration amplitude. Also, when illuminated the output of the devices drops. These effects are consistent with a piezoelectric source of the voltage.