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

Here we report near-infrared (NIR)\nlight-detecting organic phototransistors\n(OPTRs) with a gate-sensing layer (GSL) of solution-processable acid\nmolecule-bound small molecule complexes that were prepared by reactions\nof 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and tris(4-aminophenyl)amine\n(TAPA). The reaction time between TAPA and AMPSA was varied to investigate\nits influence on the optical absorption and device performance. Results\nshowed that the reaction, leading to the TAPA:AMPSA complexes, proceeded\ngradually with time by changing the solution color from dark green\nto light black. The resulting TAPA:AMPSA films exhibited additionally\ngenerated optical absorptions in the wavelength range of 600∼1100\nnm. The transistor test revealed that the devices with the 3 h-reacted\nTAPA:AMPSA layers delivered the highest drain current (1.01 μA)\nwith a reasonable on/off ratio (1.7 × 10<sup>4</sup>). The OPTRs\nwith the wet-coated TAPA:AMPSA GSLs could stably detect three different\nNIR lights (780, 850, and 905 nm) with a maximum photoresponsivity\nof 94.2 mA/W (905 nm). The TAPA:AMPSA complexes could be solution-coated\non poly(ethylene naphthalene) film substrates, leading to flexible\nOPTRs that could successfully detect the NIR light.