Solid-state dye-sensitized photovoltaic cells have been fabricated with TiO 2 as the electron conductor and CuSCN as the hole conductor. The cells show photocurrents of ≈8 mA/cm 2 , voltages of ∼600 mV, and energy efficiencies of ≈2% at 1 sun. The CuSCN was deposited into the pores of the nanoparticulate TiO 2 /dye film from dilute solution in propylsulfide. The degree of pore filling achieved is near 100% for TiO 2 films <2-µm thick and falls to ≈65% for films near 6 µm. The final drying step after the CuSCN deposition is shown to be critical; drying in vacuum or argon is required for photocurrents above 2 mA/cm 2 . The photocurrent IVs of these cells are fit to a single diode equation and the results are discussed and compared to those for equivalent photoelectrochemical cells, and similar solid cells composed of ZnO/dye/CuSCN.

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Free base 5,10,15,20-tetrakis(4-n-octylphenyl) porphyrin (H 2 TOPP) belongs to a class of self-organizing porphyrins. Since its LUMO lies above the conduction band of titanium dioxide (TiO 2 ) and its visible light absorption is very strong, sensitization of TiO 2 with H 2 TOPP thin films is possible. After spin-coating this porphyrin onto n-type TiO 2 , the Fermi-level of H 2 TOPP is measured, from which it is established that it behaves as intrinsic semiconductor, i.e., donor and acceptor densities, if present, compensate each other. Thin films of zinc 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin (ZnTCPP) are also investigated and show profound p-type character. Moreover, the LUMO of ZnTCPP is located about 0.4 eV above that of H 2 TOPP making an organic based heterostructure p-i-n solar cell possible. In this cell, H 2 TOPP is sandwiched between n-type TiO 2 and p-type ZnTCPP. The LUMO positions of these porphyrins is such that unidirectional energy transfer from ZnTCPP to H 2 TOPP occurs. By carefully comparing the photocurrent action spectra with the absorption spectra, it could be established that a built-in field in the p-i-n structure is beneficial for solarenergy conversion.