Fabrication and characteristics of Schottky diodes based on regioregular poly(3-hexylthiophene)/Al junction

Schottky diodes based on Al/poly(3-hexylthiophene), PHT/Au (or indium tin oxide (ITO)) are fabricated with various preparation conditions. The current–voltage characteristics and photovoltaic effect have been studied to elucidate the mechanisms of rectification and photocarrier generation. The PHT/Al junction prepared by spin coating of PHT on fresh Al deposited in vacuum shows the larger rectification ratio up to 105 at ±2 V than that obtained by reversed way. The results indicate that the oxidation layer of Al plays the important role for the charge injection between Al and PHT. The thickness of depletion layer due to the Schottky junction is evaluated to be 70–150 nm from the capacitance vs. reversed bias plots. The excitation spectra and PHT thickness dependence of photocurrents upon illumination to Al or Au side are also measured. The results indicate that the carrier generation occurs predominantly within the depletion layer near the Al electrode with the help of strong built-in field.