Direct tracing of the photocurrent multiplication process in an organic pigment film

The transient response of the photocurrent multiplication phenomenon at an organic/metal interface was revealed to have two components, which were identified as the primary and the subsequent multiplied photocurrents. The transient photocurrent directly traced the multiplication process, that is, the accumulation of trapped holes near the interface, which is produced by the primary photocurrent and builds up a high electric field at the interface, and then tunneling electron injection from the metal electrode to the organic layer. The onset time for multiplication was observed at 43 ms under a light intensity of 0.19 mW cm−2. The amount of charge required for multiplication onset was found to have a specific value of 30 nC cm−2, implying that an increase of the carrier generation efficiency of the primary photocurrent is expected to be effective at achieving high speed multiplication.