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

Abstract

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 ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msubsup><mi>D</mi> <mi>sh</mi> <mo>∗</mo></msubsup> <annotation>$D_{{\mathrm{sh}}}^*$</annotation></semantics> </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.