Highly Efficient Top‐Emitting Infrared‐to‐Visible Up‐Conversion Device Enabled by Microcavity Effect

Infrared (IR)‐to‐visible up‐conversion device allows a low‐cost, pixel‐free IR imaging over the conventional expensive compound semiconductor‐based IR image sensors. However, the external quantum efficiency has been low due to the integration of an IR photodetector and a light‐emitting diode (LED). Herein, by inducing a strong micro‐cavity effect, a highly efficient top‐emitting IR‐to‐visible up‐conversion device is demonstrated where PbS quantum dots IR‐absorbing layer is integrated with a phosphorescent organic LED. By optimizing the optical cavity length between indium tin oxide (ITO)/thin Ag/ITO anode and semi‐transparent Mg:Ag top cathode, the up‐conversion device yields 15.7% of photon‐to‐photon conversion efficiency from the top‐emission. The high efficiency can be achieved under a low IR transmission through the semi‐reflective anode. Finally, pixel‐free IR imaging is demonstrated using the up‐conversion device, boosting the effect of micro‐cavity on the brightness and the contrast of an IR image. High efficiency top‐emitting infrared (IR)‐to‐visible up‐conversion device is demonstrated by exploiting microcavity effect. Compared to up‐conversion device using conventional indium tin oxide (ITO) electrode, ITO/Ag/ITO reflective electrode offers a strong optical resonance toward the top side, yielding 15.7 % IR‐to‐photon conversion efficiency. Using the microcavity effect, pixel‐free IR imaging is demonstrated with higher brightness and image contrast.