Achieving Highly Sensitive Near‐Infrared Organic Photodetectors using Asymmetric Non‐Fullerene Acceptor.

Organic photodetectors (OPDs) based on non‐fullerene acceptors (NFAs) have received considerable attention because of their potential for use in various commercial applications as near‐infrared (NIR) light sensing platforms. However, recent OPDs suffer from low NIR photoresponse and large dark/noise currents with narrow bandgap organic photoactive materials. Herein, a π‐bridge molecular engineering strategy replacing alkoxythienyl with benzothiadiazole for ultra‐narrow bandgap (ultra‐NBG) NFAs is designed to achieve simultaneously high photoresponse at NIR region and low noise current density, thereby leading to excellent NIR (≈1050 nm) detectivity (D*). The newly synthesized ultra‐NBG NFAs, namely COB and CBT with optical bandgaps below 1.14 eV, present high responsivity (R) with 0.369 and 0.080 A W−1, respectively, at a wavelength of 1050 nm. Especially, with effectively suppressed noise current density, COB‐based OPD exhibits a high NIR (≈1050 nm) D* value of 2.18 × 1011 cm Hz1/2 W−1 at −0.5 V bias. The obtained R and D* values for these NFAs exceed or are comparable to those of a commercial Si photodetector at 1050 nm. This work provides important insight into the π‐bridge molecular engineering strategy for ultra‐NBG NFAs, which facilitate achieving highly sensitive NIR OPDs with high NIR photoresponse and low dark/noise current. [ABSTRACT FROM AUTHOR]