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 (𝜂 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.