Solution Processed Polymer Source‐Gated Transistors for Zero‐Power Photosensing

This study demonstrates the first solution‐processed bulk heterojunction organic source‐gated transistors (OSGTs) and photo‐OSGTs fabricated using a poly(N‐alkyl diketopyrrolo‐pyrrole dithienylthieno[3,2‐b]thiophene):[6,6]‐phenyl‐C61‐butyric acid methylester (DPP‐DTT: PCBM) blend. Copper‐electrode OSGTs fabricated alongside reference transistors with Ag contacts are investigated via electrical and optical measurements and further analysed using numerical simulations. OSGTs show uniform enhancement‐mode operation with a nominal threshold voltage of −17.4 V, deep off‐state at zero gate‐source voltage (tens of pA), channel length‐independent current in the on‐state, and low voltage saturation (saturation coefficient γ = 0.22). Cu‐contact photo‐OSGTs achieve a photo‐to‐dark current ratio (PDCR) over 3400 at zero gate‐source voltage 0 V GS , vs. V GS ∼20 V for Ag devices. Simulations show that the primary causes of current nonuniformity and occasional loss of contact control are the inhomogeneity of the source contact barrier and/or thickness of the active layer, and not the channel length. Design optimizations should consider spin‐coating thickness variability, possible Cu‐active interface effects, and leakage induced by the high electric fields present at the source edge. Performance should improve further when channel length is kept short, and contact interlayers or dual work function electrodes are adopted.