Visualizing NIR Using Monolithic QD Optoelectric Upconversion Devices in Transmissive Mode

Exploiting of near infrared (NIR) wave is under significant advances in emergence technologies related to night vision, bioimaging, wafer inspections, and security systems. The full use of NIR in such technologies eventually requires converting the "invisible" NIR electromagnetic wave to "visible (Vis)" signal. This can be attained from optoelectric upconversion device, comprising a Vis light-emitting diode (LED) tandemly stacked onto an NIR photodiode (PD). In this work, we fabricate an efficient optoelectric upconversion device based on quantum dots (PbS quantum dots for NIR detection and CdSe quantum dots for Vis output signal). Employing a semi-transparent top electrode, we demonstrate a transmissive-mode device where NIR irradiated through the bottom electrode is upconverted to Vis under bias, which is then emitted through the top electrode. Moreover, not only an upconversion device comprising a single LED stacked onto a single PD (1PD-1LED configuration) is demonstrated, but we also fabricate a tandem device comprising a single PD sandwiched between two LEDs (1PD-2LED configuration). Unlike the upconversion device in 1PD-1LED configuration where only either the electrons or holes generated from photoexcitation are exploited in generating light, the upconversion device in 1PD-2LED configuration allows converting both electrons and holes to Vis. This approach will make significant impact on improving the efficiency of optoelectric upconversion and can provide wider possibility of applications.