PHOTOGENERATION AND TRANSPORT OF CHARGE-CARRIERS IN A PORPHYRIN P N HETEROJUNCTION/

Using impedance spectroscopy, the formation of a depletion layer is de monstrated upon contacting two films of different types of porphyrins. This depletion layer can be described in the same way as in a convent ional pin heterojunction of inorganic semiconductors. From Mott-Schott ky plots the doping concentration is found to be approximate to 10(17) cm(-3) for electropolymerized ZnTHOPP films and approximate to 10(19) cm(-3) for spin-coated H2TMPyP films. Since the photocurrent action s pectra are independent of the thickness of either of the layers, we co nclude that charge separation and thus the photoactive part of the cel l are confined to the interface of both layers. For charge collection, consecutive dissociation of the electron-hole pair competes with char ge recombination. The internal field over the space charge layer cause s the photoinduced charge carriers generated at the interface to drift through the bulk layer to the electrodes.