Narrowband Detection via Charge Collection Narrowing Organic Photodetector Enabled by Low Bandgap Random Terpolymer for Biometric Sensing

Abstract Achieving spectrally selective organic photodetectors (OPDs) without using broadband‐absorbing semiconductors with input filtering is a strenuous challenge. Charge collection narrowing (CCN) is a promising strategy to obtain spectrally selective near‐infrared (NIR) OPD by adopting a thick bulk heterojunction (BHJ) as active layers. In this work, a random terpolymer comprised from a diketopyrrolopyrrole (DPP), thiophene (T) and benzothiadiazole (BT), ran DPP‐2TBT, is prepared and used as a donor material in combination with the low bandgap non‐fullerene acceptor (NFA) IEICO‐4F. OPDs with a low dark current density (6.88 × 10 −9 A cm −2 ) and a 68 nm full‐width‐at‐half‐maximum (FWHM) narrowband response (R = 0.13 A W −1 at 916 nm) in the near‐infrared are achieved. Finally, an application of the OPD as a biometric heart‐rate sensor via photoplethysmography for real‐time monitoring is demonstrated.