Non-Halogenated Solvent Processed Shortwave Infrared Organic Photodetectors Using Sub-1 eV Bandgap Acceptor with Cyano Substitution

Abstract

Shortwave infrared (SWIR) organic photodetectors (OPDs) offer significant potential but face persistent challenges such as limited responsivity and high noise under reverse bias. This work presents the development of high-performance OPDs for SWIR sensing, leveraging a newly designed non-fullerene acceptor (NFA) named 6CN. The 6CN molecule, featuring a fused-cyclopentadithiophene (fCPDT) core and cyano-substituted pi-bridges, exhibits an ultra-narrow optical bandgap of approximate to 0.98 eV, enabling efficient SWIR absorption up to 1250 nm. When blended with the PTB7-Th polymer donor, the resulting bulk-heterojunction (BHJ) demonstrates strong charge transfer, broad spectral coverage, and robust charge transport. Notably, device fabrication employs the environmentally friendly solvent o-xylene without halogenated additives, yielding OPDs with superior photoresponse compared to those processed from conventional chlorinated solvents. The o-xylene processed devices achieve high responsivity (approximate to 0.2 A W-1 at 1200 nm) and specific detectivity exceeding 3 x 1011 Jones across 300-1200 nm, representing a significant advance for eco-friendly, flexible SWIR photodetection technologies.