High-Sensitivity Solution-Processed Organic Phototransistor Based on a Bulk Heterojunction with a Persistent Radical...

Area of Science:

• Materials Science
• Organic Electronics
• Photodetectors

Background:

• Bilayer organic phototransistors (OPTs) separate charge transport and light sensing into distinct layers for optimization.
• Current solution-processed OPTs often rely on fullerene derivatives or nonfullerene acceptors in the bulk heterojunction (BHJ) light-sensing layer.
• Limited choices for electron acceptors restrict the sensitivity and performance of these devices.

Purpose of the Study:

• To investigate the use of an organic persistent radical as an electron acceptor in the BHJ light-sensing layer of solution-processed bilayer OPTs.
• To explore the impact of radical acceptor incorporation on device morphology, charge transport, and photosensitivity.
• To evaluate the stability and performance of OPTs utilizing this novel acceptor material for near-infrared (NIR) detection.

Main Methods:

• Synthesized and coupled an organic persistent radical with a low-band-gap polymer at varying donor:acceptor ratios.
• Fabricated bilayer OPTs incorporating the donor-acceptor BHJ light-sensing layer.
• Characterized device morphology using techniques suitable for BHJ analysis.
• Performed charge-selective device measurements in the space-charge limited current (SCLC) range to assess charge transport.
• Tested device performance under NIR irradiation, measuring photosensitivity and photostability.

Main Results:

• The organic radical, when used as an electron acceptor at a 1:3 donor:acceptor ratio, formed isolated domains within the BHJ.
• This morphology and the radical's strong electron-accepting properties facilitated efficient electron trapping and hole transport.
• The resulting OPT demonstrated high photosensitivity (P = 1 × 10^5) to NIR light (2 mW/cm^2).
• The persistent radical exhibited excellent chemical and photostability, contributing to the device's long-term operational stability.

Conclusions:

• Organic persistent radicals are viable and effective electron acceptors for BHJ light-sensing layers in solution-processed bilayer OPTs.
• The unique morphology and electronic properties of the radical acceptor enable high-performance NIR photodetection.
• This work expands the range of materials for organic photodetectors and offers a pathway to highly sensitive and stable NIR sensing devices.