Light-Induced Generation of Charge Carriers in Porphyrin Solids Doped with Electron-Accepting and Donating Molecules

Fluorescence and photocurrent generation efficiencies of thin films of 5,10,15,20-tetraphenylporphyrin (TPP) and its zinc complex (ZnTPP) doped with electron-accepting and -donating molecules were investigated to get an insight into a charge-carrier generation in organic solid films upon irradiation. Photogeneration of charge carriers in I2-doped ZnTPP solids was found to consist mainly of a direct ionization process via an excited singlet state of ZnTPP while that in TPP solids was consistent with an exciplex formation model. From a practical view point, the doping of acceptor molecules into p-type porphyrin solids was effective to improve photovoltaic efficiencies of Al/porphyrin/Au sandwich-type cells.