Electro‐optical Charge Trapping in Zinc Porphyrin Films on Indium Tin Oxide and  / SiO2 / Si

A thin film‐of zinc octakis (β‐octyloxyethyl) porphyrin (ZnOOEP) is capable of trapping and detrapping charge in an appropriate electric field under irradiation. An effective charge capacity of the order of 30 μC/cm 2 or 10 18 charges/cm 3 was obtained with sandwich structures of ITO/ZnOOEP/ITO (where ITO is indium tin oxide) under a bias of 10 V with irradiation. Cells with the configuration were also fabricated. When an electric field was applied across this cell in the dark, a small amount of charge was stored, as in a conventional capacitor. However, the charge stored under the same conditions with irradiation of the photoconductive ZnOOEP was three orders of magnitude higher. Trapped charge produced under illumination was not removed under short‐circuit conditions in the dark, suggesting that this phenomenon could be used for information storage.