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.