Novel ambipolar polymers for detection beyond 1000 nm with organic phototransistors

Organic phototransistors (OPTs) hold significant promise for cost-effective, flexible optoelectronic applications, particularly in Shortwave-Infrared (SWIR) detection, which is crucial for applications such as health monitoring, communications, and artificial vision. Traditional OPTs often rely on unipolar materials, limiting their efficiency by utilizing only one type of charge carrier. In contrast, ambipolar organic semiconductors (OSCs), transporting both electrons and holes, can fully harness photogenerated carriers, thereby enhancing device performance. Here, high-performance, solution-processed ambipolar single-component SWIR OPTs are demonstrated by fine-tuning the number of fused thiophene rings in donor-acceptor (D-A) conjugated polymers utilizing thiadiazoloquinoxaline-unit (TQ) as the electron-deficient unit. Through systematic polymer characterizations and optoelectronic device characterizations it was revealed that three fused thiophene rings (TQ-T3) delivered ambipolar NIR phototransistors with well-balanced hole and electron mobilities of 0.03 and 0.02 cm² V^-1 s^-1 and the highest reported specific detectivity of 2 × 10⁸ Jones (at 1100 nm), with external quantum efficiency of 1400% and 1200% for the p-type and n-type single-component active layer material, respectively. These findings contribute to advancing the design of efficient ambipolar OPTs for SWIR detection, with potential applications in imaging and sensing technologies.