Near-Infrared Organic Phototransistors with Solution-Processable Acid Molecule-Bound Small Molecule Complexes

Here we report near-infrared (NIR) light-detecting organic phototransistors (OPTRs) with a gate-sensing layer (GSL) of solution-processable acid molecule-bound small molecule complexes that were prepared by reactions of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and tris(4-aminophenyl)amine (TAPA). The reaction time between TAPA and AMPSA was varied to investigate its influence on the optical absorption and device performance. Results showed that the reaction, leading to the TAPA:AMPSA complexes, proceeded gradually with time by changing the solution color from dark green to light black. The resulting TAPA:AMPSA films exhibited additionally generated optical absorptions in the wavelength range of 600∼1100 nm. The transistor test revealed that the devices with the 3 h-reacted TAPA:AMPSA layers delivered the highest drain current (1.01 μA) with a reasonable on/off ratio (1.7 × 104). The OPTRs with the wet-coated TAPA:AMPSA GSLs could stably detect three different NIR lights (780, 850, and 905 nm) with a maximum photoresponsivity of 94.2 mA/W (905 nm). The TAPA:AMPSA complexes could be solution-coated on poly(ethylene naphthalene) film substrates, leading to flexible OPTRs that could successfully detect the NIR light.