Dark and photovoltaic properties of doped tetraphenylporphyrin sandwich cells. Part 2.—Properties of illuminated cells

Abstract

The photovoltaic properties of electron-acceptor-doped thin-film sandwich cells of the structure Al|Al₂O₃|MTPP (meso-tetraphenylporphyrin)|Au, where M = Zn, H₂, Cu, Ni or Co, fabricated using optimised doping procedures, and tested under high vacuum, are described. A wide variation in photovoltaic efficiency is observed with variation of the porphyrin central substituent, paralleling trends of device stability and affinity of the porphyrins to the dopant vapour. An exponential relationship is found between the value of peak quantum efficiency and the potential of the porphyrin first ring oxidation. The results indicate that the charge carrier photogeneration mechanism involves the formation of a weak ground-state donor-acceptor complex between the porphyrin and dopant molecules. Enhanced carrier generation is observed at wavelengths above 750 nm, possible resulting from the direct formation of triplet exciton states. Values of Soret band quantum yield of iodine-doped devices are 0.48, 0.083, 0.029, 0.026 and 0.018% for ZnTPP, H₂TPP, CuTPP, NiTPP and CoTPP, respectively, and 0.22 and 0.04% for oxygen–water vapour-doped ZnTPP and H₂TPP cells, respectively.