Molecular‐Device Co‐Engineering of Ultra‐Low Dark Current SWIR Organic Photodetectors for High‐Quality Blood‐Pressure Monitoring and Optical Communication

The limited noise-responsivity balance in Short-wave infrared (SWIR) organic photodetectors (OPDs) restricts their biomedical and optoelectronic applications. In this study, this challenge is addressed through molecular-device co-engineering by designing two fluorinated narrow-bandgap non-fullerene acceptors (BTT-DTPn and BTT-DTPn-2F) coupled with solvent vapor annealing (SVA), achieving low noise and high detectivity in SWIR OPDs. The optimized devices based on BTT-DTPn-2F, which features enhance π-π stacking due to terminal fluorination, extend its absorption capability to 1300 nm. Under -0.1 V bias, the SVA-processed BTT-DTPn-2F devices demonstrate an ultra-low dark current (J_d) of 4.93 × 10^-8 A cm^-2 and exhibit a suppressed trap density of states (tDOS) reduced by an order of magnitude, achieving a shot-noise limited detectivity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>D</mml:mi> <mml:mi>sh</mml:mi> <mml:mo>∗</mml:mo></mml:msubsup> <mml:annotation>$D_{{\mathrm{sh}}}^*$</mml:annotation></mml:semantics> </mml:math> ) of 7.19 × 10¹¹ Jones at 1200 nm. The synergy of molecular design and post-processing enables an ultra-fast response time (1.44/1.20 µs rise/fall) and a record-high -3 dB cutoff frequency (f_{-3 dB}) of 648 kHz, demonstrating remarkable performance for SWIR OPDs. These advancements facilitate two groundbreaking applications: deep-tissue photoplethysmography (PPG) for cuff-less blood pressure monitoring and high-speed, real-time SWIR optical communication. This methodology presents a general strategy to harmonize molecular design with device fabrication in SWIR OPDs.