Short-Wave Infrared-Sensing Organic Phototransistors with a Triarylamine-Based Polymer Doped with a Lewis Acid-Type Small Molecule

Here, we report that a triarylamine-based polymer, poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (PolyTPD), is effectively doped with tris(pentafluorophenyl)borane (BCF) and the doping level is dependent on the molar ratio of BCF to PolyTPD (repeating unit). The doping reaction is performed at 25 °C at the solution states using chlorobenzene solvent by varying the BCF molar ratio up to 2.0. The resulting PolyTPD:BCF films show new broad optical absorption peaks at a wavelength of λ = 1000-3300 nm, covering the full range of short-wave infrared (SWIR, λ = 1400-3000 nm), which is stronger at a higher BCF molar ratio. Spectroscopic characterizations confirm the generation of radicals (single electrons) in PolyTPD by BCF doping, which resulted in a gradual shift of the highest occupied molecular orbital (HOMO) energy level with the BCF molar ratio. The PolyTPD:BCF films are applied as a gate-sensing layer (GSL) in the geometry of organic field-effect transistors (OFETs), leading to SWIR-sensing organic phototransistors (OPTRs). The optimized SWIR-OPTRs with the PolyTPD:BCF GSLs (BCF molar ratio = 0.5) can detect SWIR light with maximum photoresponsivities of 583.4 mA/W (λ = 1500 nm), 695.4 mA/W (λ = 2000 nm), and 829.4 mA/W (λ = 2500 nm).