High-Performance Phototransistor Based on a 2D Polybenzimidazole Polymer.

Area of Science:

• Materials Science
• Optoelectronics
• Polymer Chemistry

Background:

• Photodetectors are crucial for converting light to electrical signals in optoelectronics.
• High-performance phototransistors require materials with excellent charge carrier mobility and photoresponse.
• Achieving both properties simultaneously in a single material presents significant challenges due to inherent trade-offs.

Purpose of the Study:

• To introduce a novel 2D polymer (2DPBI) with a π-conjugated photoresponsive porphyrin motif.
• To synthesize few-layer, crystalline 2DPBI films with large domain sizes.
• To investigate the optoelectronic properties and performance of 2DPBI in phototransistors.

Main Methods:

• Synthesis of few-layer, crystalline 2DPBI films on a water surface.
• Characterization using Terahertz spectroscopy and temperature-dependent photoconductivity measurements.
• Fabrication and testing of 2DPBI-based phototransistors.

Main Results:

• 2DPBI films exhibited large crystalline domain sizes (110–140 µm²) over a significant area (≈28 cm²).
• The material possesses a narrow direct band gap (≈1.18 eV), high absorption coefficient (up to 10⁶ cm⁻¹), and excellent charge carrier mobility (≈240 cm² V⁻¹ s⁻¹).
• 2DPBI phototransistors achieved high performance metrics: on/off ratio > 10⁸, photosensitivity of 1.08 × 10⁷, response time of 1.1 ms, and detectivity of 2.0 × 10¹³ Jones.

Conclusions:

• The synthesized 2DPBI demonstrates superior optoelectronic properties, including high charge carrier mobility and robust photoresponse.
• 2DPBI-based phototransistors exhibit performance comparable to silicon and surpass other few-layer 2D materials.
• 2DPBI represents a promising new material platform for the development of next-generation optoelectronic devices.