Photomultiplication‐Type Broadband Organic Photodetectors With an ON/OFF Current Ratio Exceeding 79 000 Enabled by Self‐Assembled Ultra‐Thin Layer

ABSTRACT Photomultiplication type broadband organic photodetectors (PM‐BOPDs) were fabricated by employing one wide bandgap polymer P3HT and one narrow bandgap non‐fullerene acceptor BTPSe‐Ph4F with a weight ratio of 100:2 as active layers. Plenty of isolated electron traps will be formed in the active layers due to the rather low BTPSe‐Ph4F content, leading to poor electron transport channels and efficient hole transport channels in the P3HT:BTPSe‐Ph4F (100:2, w/w) active layers. Photogenerated electrons will be trapped in the isolated BTPSe‐Ph4F; the trapped electrons near the Al electrode will induce interfacial band bending for hole tunneling injection from the external circuit. The dark current density of PM‐BOPDs can be further suppressed by ∼2 orders of magnitude by employing a 3‐BPIC‐F self‐assembled ultra‐thin layer to replace PEDOT:PSS. The optimal PM‐BOPDs display an external quantum efficiency of 2970%, an on/off current ratio of 79 020, and specific detectivity of 1.16 × 10 13 Jones at a frequency of 90 Hz at 625 nm light under −10 V bias, indicating strong weak‐light sensitivity of PM‐BOPDs. The optimized PM‐BOPD was employed for photoplethysmography (PPG) monitoring. PPG signals were successfully recorded during rest and exercise, and their characteristics were analyzed to extract heart rate information and identify characteristic pulse wave features.