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

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.