Ultrafast and broadband photodetectors based on Cs₂AgBiBr₆/PM6:L8-Bo heterojunction for photoplethysmography sensor

Broadband photodetectors with low toxicity, high sensitivity, and excellent stability possess irreplaceable application value in the field of biomedical sensing. This work reports a high-performance lead-free broadband photodetector based on the Cs₂AgBiBr₆/PM6:L8‑BO heterojunction active layer, which ingeniously integrates the outstanding structural stability and strong visible-light absorption of lead-free double perovskite Cs₂AgBiBr₆ with the broad near-infrared (NIR) absorption advantage of organic bulk heterojunction (BHJ) PM6:L8‑BO. The device achieves a continuous spectral response from 300 to 1000 nm, with maximum external quantum efficiency (EQE) reaching 77% at 750 nm, and remains 38% at 850 nm in the NIR region. It also exhibits high specific detectivity (D*) of 7.59 × 10¹² Jones, an ultrafast response speed of 7 ns/550 ns, and a large linear dynamic range (LDR) of 103 dB. Furthermore, a photoplethysmography (PPG) health monitoring system is constructed based on this photodetector, realizing stable human fingertip pulse signal acquisition and accurate heart rate calculation. This study offers a feasible strategy for developing low-toxicity, high-performance broadband photodetectors and effectively promotes the application of lead-free perovskite materials in wearable health monitoring and biomedical sensing.