Rational Terminal Engineering Enabled Vulnerable Exocyclic-Vinyl-Free Nonfullerene Acceptors for Sensitive and...

Area of Science:

• Materials Science
• Organic Electronics
• Optoelectronics

Background:

• Acceptor-donor-acceptor (A-D-A) nonfullerene acceptors (NFAs) have boosted near-infrared organic photodetector (NIR OPD) performance.
• Structural instability from exocyclic vinyl bridges in NFAs limits material and device durability.

Purpose of the Study:

• To overcome the instability challenge in NFAs by designing exocyclic-vinyl-free materials.
• To synthesize and evaluate novel electron-withdrawing 2-(2-bromo-3-cyano-8H-indeno[2,1-b]thiophen-8-ylidene)malononitrile (ITC2H) based NFAs for enhanced NIR OPDs.

Main Methods:

• Developed a terminal engineering strategy to create exocyclic-vinyl-free NFAs.
• Synthesized the novel ITC2H building block and its derivatives, such as BTP-ITC2H.
• Fabricated and characterized self-powered organic photodetectors using the new materials.

Main Results:

• The BTP-ITC2H derivative showed improved chemical/photostability, crystallinity, broader absorption, better miscibility, and lower reorganization energy compared to classical NFAs.
• Optimized nanomorphology led to suppressed trap states and enhanced charge transport.
• Achieved a self-powered OPD with dark current density (Jd) of 3.3 × 10^-11 A cm^-2 and detectivity (D*sh) over 10^13 Jones (310-910 nm), with a 141 dB linear dynamic range.
• Extended response to 1300 nm using halogenated ITC2H analogues, maintaining high detectivity.

Conclusions:

• The terminal engineering strategy successfully created stable, high-performance exocyclic-vinyl-free NFAs.
• The new materials significantly advance the stability and performance of NIR organic photodetectors.
• This molecular engineering paradigm offers critical insights for developing robust organic optoelectronics.