Photovoltaic Properties of Porphyrin Thin Films Mixed with o-Chloranil

By mixing Zntpp solid with o-chloranil, the rectification and photovoltaic properties of Al/porphyrin/Au sandwich-type cell are improved (Zntpp: 5, 10, 15, 20-tetraphenylporphyrinatozinc). The improvement may be mainly attributable to an increase in the hole concentration as the majority carrier because of the electron transfer from Zntpp to o-chloranil in the ground state. In addition, by mixing H2tpp solid with o-chloranil, the short circuit photocurrent of the sandwich-type cell increases although the rectification property is hardly improved (H2tpp: 5, 10, 15, 20-tetraphenylporphyrin). The fluorescence intensity, the short circuit photocurrent and its temperature-dependence for various porphyrin solids mixed with o-chloranil are measured in order to clarify the photogeneration mechanism of charge carriers. The results suggest strongly that an exciplex formed between H2tpp and o-chloranil molecules contributes to the photogeneration of charge carriers.