Solution Processable Phototransistors with Ultra-High Responsivity Enabled by Hierarchical Poly(3-Hexylthiophene) Carbon Nanotube Composites

Photodetectors are a key sensing component in enabling emerging technologies. For weak light detection, phototransistors with high responsivity are needed. Furthermore, the ability to fabricate phototransistors using solution processing techniques will enable new form factors, including flexible and large-area devices. In this work, a novel approach for synthesizing a photosensitive organic/inorganic hybrid semiconducting thin film through solution processing is introduced. The approach involves hierarchical patterning of semiconducting carbon nanotubes (CNTs) with poly(3-hexylthiophene-2,5-dyl) (P3HT) through solution-phase heterogeneous crystallization. The fabricated hybrid phototransistors are qualified through electrical testing at varied illumination profiles within the visible light range. At a wavelength of 470 nm with an optical excitation power of 0.37 µW cm⁻², the device exhibits photoresponsivity of 3.53 × 10⁵ AW⁻¹, surpassing other solution-processed, non-lead-containing devices in the literature. The optical response extends from both photogating (low excitation power) and photon-induced carrier generation (high excitation power). The detectivity of the device is ≈8.7 × 10¹⁰ Jones. The transient response includes a rise time of 100 ms and a fall time of 200 ms which is similar to the metrics of other low-dimensional photodetectors. These findings highlight the prospects of the solution-processed P3HT/semi-CNT hybrid platform for advanced photodetection applications with flexible and large-area form factors.