Photocurrent multiplication at organic/metal interface and surface morphology of organic films

Photocurrent multiplication occurring at an organic pigment/metal interface was revealed to be strongly dependent on the surface morphology of the org anic film. The polycrystalline pigment film having a microscopically rough surface showed large photocurrent multiplication reaching the gain of more than 10(4)-fold, while amorphous pigment film having a smooth surface and A u film showed little multiplication. Because of imperfect contact with an A u electrode deposited on a bumpy film surface, there exists a large number of blind alleys (structural trap) which can hold off photogenerated holes. The accumulation of hole carriers builds up high electric field at organic/ metal interface and triggers the tunneling injection of electrons from the Au electrode. Emergence of the photocurrent multiplication phenomenon was s uccessfully demonstrated to be controllable through changing the organic fi lm morphology. The present results also pointed out the existence of a larg e number of blind alleys acting as structural traps at organic/metal interf ace. (C) 2000 American Institute of Physics. [S0021-8979(00)04507-2].