Flexible NIR-to-Blue Quantum Dot Up-Conversion Devices for Wearable Bio-Imaging and Monitoring

Near infrared (NIR)-to-visible up-conversion devices (UCDs) offer significant advantages in pixelless bio-imaging and monitoring. Herein, a flexible NIR-to-blue quantum dot (QD) UCD is developed by directly stacking an organic bulk-heterojunction (BHJ) photodetector unit with an environmentally-friendly ZnSe/ZnS QD light-emitting unit in tandem. Aiming at the interconnection layer (ICL) that couples these two units, an Mg-doped ZnO ICL is rationally designed to achieve high conductivity and a low work function, facilitating the rapid transport of photo-generated electrons and their efficient injection into the QD emitting layer. Importantly, Mg-passivated ICL with fewer surface defects alleviates the exciton quenching at the QD/ICL interface and suppresses the undesired charge recombination at the ICL/BHJ interface. The resultant QD-UCDs enable a high photon-to-photon conversion efficiency (? P-P ) of 8.68%, which is ≈3 times higher than that with un-doped ICLs (2.91%). The flexible QD-UCDs can readily measure human heart rate and provide high-contrast microscopic imaging of various biological tissues.