Diodes with an active layer of solution processed zinc oxide (ZnO) nanoparticles and polystyrene are studied. Poly(3,4-ethylenedioxythiophene)- polystyrenesulfonate (PEDOT:PSS) on indium doped tin oxide (ITO) is used as the bottom electrode and aluminum or calcium are used as top electrode. Pristine devices show diode behavior in their current-voltage characteristics. The conductivity of the device in reverse bias can be raised three orders of magnitude by applying a positive voltage or by illumination with UV light. In this high conductivity state we observe reversible electronic memory effects. The electronic memory effects are attributed to a reversible electrochemical process at the PEDOT:PSS/ZnO interface. Memory effects in diodes with Al and Ca metal electrode are found to be very similar, consistent with the view that the memory effects arise at the PEDOT:PSS/ZnO interface.