A non-ideal bias dependence of the inner electric field in Au/Zn-phthalocyanine/Al photovoltaic cells studied by electroabsorption and photocurrent measurements

Electroabsorption (EA) and photocurrent measurements are done for Au/Zn-phthalocyanine (ZnPc)/Al sandwich cells in order to study the bias dependence of the inner electric field in the ZnPc layer. The bias dependence of the EA signal intensity and photocurrent is not explained by the conventional models for the inner electric field in the following features. 1) The EA intensity and the photocurrent disappear at different bias voltages, i.e. 1.24 and 0.47 V, respectively. 2) The EA intensity does not have a simple linear dependence on the bias voltage. 3) The photocurrent is kept zero with the bias voltage higher than 0.47 V. The results are consistently explained by a model in which an interfacial layer and surface states exist at the ZnPc/Al junction.