High detectivity ternary near-infrared organic photodetectors based on double electron transport layer for health monitoring†

Near-infrared organic photodetectors (NIR-OPDs) have significant potential for applications in biological imaging and medical diagnostics. However, the commonly high dark current density (J_D) and poor charge transport restrict the specific detectivity of NIR-OPDs. In this study, PBDTDPP is incorporated as the third component in PTB7-Th:PC₆₁BM-based OPDs to achieve a broader visible-near-infrared (vis-NIR) response. By varying the blend ratio, the ternary blend promotes the formation of a cascade energy heterojunction to enhance charge transport. Utilizing a PFN-Br/ZnO double electron transport layer (ETL) not only suppresses charge injection from the cathode, but also reduces trap density and minimizes charge recombination losses, thus improving charge transport and collection efficiency. Consequently, the PFN-Br/ZnO device achieves an ultralow J_D of 4.72 × 10⁻¹⁰ A cm⁻², a high exceeding 10¹³ jones and a −3 dB cutoff frequency (f_−3 dB) surpassing 1 MHz. Furthermore, the NIR-OPD devices have been successfully applied in arterial pulse monitoring sensors for health monitoring.