The effect of hydrogen on the photoconductivity of porphyrin nanowires

Nanowires that are self-assembled from Tetrakis(4-sulfonatophenyl)porphine (TPPS4) have shown a remarkable range of photoelectronic behaviors, including slow growth of photoconductivity over several days of illumination and high sensitivity to atmospheric oxygen[1]. Preliminary experiments in our group have shown that atmospheric hydrogen gas dramatically increases the conductivity and photoconductivity of the nanowires. We propose that the increase is due to a lowering of the height of Schottky barriers formed at the junctions of the nanowires with the AuPd electrodes. However, more recent experiments showed a surprisingly complex behavior, in which, after introduction of the hydrogen, the conductivity first went up slightly, then down slightly, then (after a delay of a few hours) up dramatically, and finally down dramatically. We propose that this complex behavior is due to a combination of the hydrogen and residual oxygen which outgasses from our sample chamber.

1- C.K. Riley, J. Phys. Chem. C 2010, 114, 19227–19233