Photoinduced charge transfer in bifunctional molecules with both electron donor and accepter groups

Charge transfer within photo-active molecules is one of the important mechanisms for achieving photo-sensitive devices. We have employed two kinds of material, C$_{60}$- diphenylaminofluorene-C$_{18}$ [1] and an intramolecularly hydrogen-bonded, porphyrin-terminated dendron with a focal napthylene diimide [2]. Both have electron donor and accepter groups in a molecule. For the former, we made the structure by sandwiching a film of the photo-active material between ITO electrodes to measure photoconductivity spectrum in near- UV/Vis/near-IR range. Photoconductivity is on order of $10^{-12} $S/cm and it is dependent on light intensity and wavelength. As light intensity increases, photoconductivity increases for $\lambda \sim$ 350nm, but it decreases for $\lambda \sim$ 650nm. For the latter, we made photovoltaic cells with aluminum and ITO electrodes. IV characteristics were measured at each spectrum peak of donor (414, 516, 552, 590, 646nm) and accepter (360, 382nm) absorption. At 516, 552 nm, the devices shows highest power conversion efficiency with V$_{oc} \sim$ 0.8 V and J$_{sc} \sim 5 \times 10^{-8}$A/cm$^2$. The mechanisms and measurements of temperature dependence will be discussed. [1] H. Luo {\it et. al}, J. Phys. Chem. B 107, 9312 (2003). [2] Y. Wu {\it et. al.} to be published