Highly stable photomultiplication-type organic photodetectors with single polymers containing intramolecular traps as the active layer

Abstract

Photomultiplication-type organic photodetectors (PM-OPDs) have attracted enormous interest owing to their high sensitivity toward weak light and, especially, due to their excellent parasitic stability when using a single polymer as the active layer. Herein, three different polymers, DCP1-3, were synthesized with different amounts of PC₆₁BM pendants as intramolecular traps, and they were successfully applied to high-stability PM-OPDs. Photogenerated electrons will be trapped by suspended PC₆₁BM in the polymers to induce interfacial band-bending for hole tunneling injection, and the injected holes can be efficiently transported along the channels of the polymer under bias. The thickness of the ultrathin PFN–Br interfacial layer was optimized to decrease the dark current density. An EQE of 19100% at 365 nm was obtained for DCP3-based PM-OPDs using PFN–Br as the interfacial layer under a bias of 20 V. The optimized PM-OPDs exhibit excellent stability, with no photocurrent decay after 70 days of storage in a nitrogen-filled glove box, which is attributed to the locking of donor and acceptor segments through covalent links in the polymer. The optimized PM-OPDs can be employed to measure the heart rate (HR) of humans under different pulsatile conditions, indicating the promising application prospects of PM-OPDs with a single polymer as the active layer.