Enhanced Photoresponse of a Solution-Gated Organic Phototransistor Using a Plasmonic Organic Solar-Cell Gate

Abstract A solution‑gated organic phototransistor (SGOPT) was developed by integrating a plasmonic P3HT:PCBM organic solar cell (OSC) gate with a P3HT/graphene oxide (GO) field‑effect transistor through a phosphate‑buffered saline electrolyte. The OSC converts incident light into an open‑circuit photovoltage delivered to the transistor channel via the electrolyte/GO interface, and its grating structure enables propagating surface plasmon (PSP) excitation. P‑polarized reflectance from the ITO side exhibited angle‑dependent modulation over 500–700 nm, while FDTD calculations revealed an RP/RS minimum near 627 nm and p‑selective interfacial field localization at 620 nm, consistent with PSP-assisted coupling. Measurement states distinguished direct FET photoresponse, OSC‑only photogating, and simultaneous OSC/FET illumination, the latter producing the largest drain‑current change. P‑polarized illumination generated a stronger response than s‑polarized illumination, and 620‑nm light produced a larger response than 500‑nm light. These optical and electrical trends are consistent with a PSP‑assisted contribution.