Enhanced photocurrent quantum yield by electronic interaction between zinc porphyrin and rhodamine B molecules in Al/Dye/Au sandwich-type solar cell

The enhanced photocurrent is observed with the mixed solid of 5,10,15,20-tetraphenylporphyrinatozinc (Zntpp) and rhodamine B (RhB) compared with the pure Zntpp and RhB solids in Al/dye/Au sandwich-type solar cell. The photocurrent quantum yield has a maximum at the mixing ratio (R) of 0.5-0.8 defined as the molar ratio of porphyrin to total dye. The enhancement arises from the decrease of the series resistance by 2 orders of magnitude upon mixing Zntpp and RhB for the best cells. For the Al/mixed solid (R = 0.57)/Au cell, the short-circuit photocurrent quantum yield (phi) of 14.7%, the open-circuit photovoltage (V-proportional to) of 0.90 V, the fill factor (ff) of 0.18, and the energy conversion yield (eta) of 0.82% are obtained when illuminated with 440 nm monochromatic light of 14.7 mu W cm(-2) intensity at the Al/dye interface, and the values of phi = 9.1%, V-proportional to = 0.90 V, ff = 0.19, and eta = 0.72% are obtained when the sample is illuminated with 570 nm monochromatic light of 32.4 mu W cm(-2) intensity. It is found from the absorption spectra of the mixed film and the cyclic voltammograms of the mixture in dichloromethane that a ground-state complex is formed between Zntpp and RhB molecules. Larger specific conductivity is obtained with the mixed solids of R = 0.6-0.8 than with the pure Zntpp and RhB solids because the ground-state complex is easily oxidized and holes as the majority carrier consequently increase. In addition, the enhancement of the photocurrent of the solar cell made up of the mixed solid is interpreted in terms of the increased potential gradient in the Schottky barrier and the ease of the charge separation of an excited state formed from the ground-state complex.