Near-Infrared Organic Photodetectors with Ultralow Dark Current for Photoplethysmogram Sensor and Optical Communication Applications

Suppressing dark current (and noise) in organic photodetectors (OPDs) is crucial to the design of highly sensitive devices. Currently, the physical mechanisms that contribute to the dark current in OPDs are clear, which include shunt leakage current originating from poor-quality film, charge injection under a reverse bias voltage owing to inadequate barrier height between electrode and semiconductor, trap-induced current from trapped carriers, etc. However, the main obstacle to the development of highly sensitive OPDs has been the lack of trap state density control while maintaining a reduced interfacial trap-controlled charge injection; these are particularly important for near-infrared (NIR) OPDs that suffer from various sources of electronic noise. Herein, we report a ternary blend strategy by incorporating a third component polymer acceptor N2200 into a NIR OPD based on the blend of a wide bandgap polymer donor PCE10 and a narrow bandgap small molecule acceptor COTIC-4F. The addition of 17 wt % N2200 leads to a decrease in the trap density from 5.25 × 10¹⁵ cm^-3 to 2.16 × 10¹⁵ cm^-3. The best-performing device shows an ultralow dark current density of 3.21 × 10^-10 A cm^-2 under a bias of -0.1 V and a high specific detectivity of more than 10¹³ Jones over a broad spectral range covering 300-1100 nm. We further demonstrated the feasibility of a photoplethysmogram (PPG) sensor and optical communication applications with these highly sensitive NIR OPDs.