Boosting the photosensitivity of organic phototransistors with photomultiplication via Corbino configurations

An organic phototransistor (OPT) with a photomultiplication mechanism is studied, where a bulk-heterojunction of C70 and 1,1-bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane is used as a channel and a light-absorbing layer with an Al Schottky contact as source/drain electrodes. The light absorption in the source-side region is found to dominate the photomultiplication effect. In addition, the source electrode area that is up to 100 μm away from the channel is identified as the most effective region in the OPTs with contact-limited operation used in this study. Therefore, to maximize the light-sensing performance of the contact-limited OPTs, we propose Corbino source/drain geometries that have a larger source electrode area than that of the drain electrode. The Corbino-type OPTs show improved photo-response properties proportional to the relative increment of the source-side area, reaching 1.7-fold higher performance in terms of photosensitivity compared to the conventional lateral-type OPTs.