Low-color-temperature white QD light-emitting electrochemical cells

Low-color-temperature white light-emitting devices have become popular in healthy lighting applications since blue light affects human physiology and psychology significantly. Solid-state white light-emitting electrochemical cells (LECs) show promising advantages of simple solution fabrication processes, low operation voltage, and compatibility with air-stable cathode metals, which are beneficial in lighting applications. However, low-color-temperature white LECs have been rarely studied so far. In this work, low-color-temperature white LECs based on blue, green, yellow, and red CdZnSeS/ZnS core-shell quantum dots (QDs) are demonstrated. The proposed white LEC contains an emissive layer of mixed blue, green, yellow, and red QDs and a carrier injection layer of an ionic transition metal complex (iTMC). The iTMC layer forms the electrochemically doped layers and improves the carrier injection efficiency under a bias. The white QD LECs exhibit white electroluminescence (EL) with a low correlated color temperature (CCT) < 1800 K and a high color rendering index (CRI) > 90 under lower currents. However, increasing the device current accompanies by the enhancement of the brightness results in more emission from the wider-energy-gap QDs and thus the CCT increases significantly (>3000 K). Removing the blue QDs from the white QD LECs not only prevents the CCT from increasing under a higher device current but also improves the device efficiency. The CCTs of EL spectra from the proposed white QD LECs are among the reported lowest values of the white LECs and thus reveal excellent color tuning feasibility of these mixed QD emissive layers.