Photoconductivity in Sandwich Cells with Langmuir-Blodgett Films of Phthalocyaninato-Polysiloxanes

Abstract

Charge carrier photogeneration in sandwich cells containing Lagmuir-Blodgett multiassemblies of tetramethoxy-tetra(octyloxy)phthalocyaninatopolysiloxane (PcPS) has been investigated with respect to the spectral response and light flux dependence. The films were contacted using Au or Pt bottom electrodes and Bi or Al top electrodes. The gain factors showed the largest value, close to 1%, at 325nm. The DC current-voltage curves of the cells with Al-electrode show rectification behavior. The rectification ratio (forward- vers. reverse-bias current) was typically higher than 40 for the ±0.5V applied. Under illumination, the devices worked like photocells giving open circuit voltage ∼0.25V (Al-electrode negative) and a fill factor value 0.43. A mechanism of the charge carrier photogeneration process is proposed that includes free electron generation from ionized PcPS - oxygen complexes at the Al/PcPS interface, electron transfer to the Al-electrode and relaxation of the Schottky space-charge region with subsequent oxidation of the Al-electrode.