All solution-processed white quantum-dot light-emitting diodes with three-unit tandem structure

Quantum-dot light-emitting diodes (QLEDs) are promising candidates for next generation displays. White QLEDs which can emit red, green and blue colors are particularly important; this is because the combination of white QLEDs and color filters offers a practical solution for high-resolution full-color displays. In this work, we demonstrate all-solution processed three-unit (red/green/blue) white tandem QLEDs for the first time. The white tandem devices are achieved by serially connecting the red bottom sub-QLED, the green middle sub-QLED and the blue top sub-QLED using the inter-connecting layer (ICL) based on ZnMgO/PEDOT:PSS heterojunction. With the proposed ICL, the two-unit tandem QLEDs exhibit a high current efficiency of 22.22cd/A, while the three-unit white QLEDs exhibit evenly separated red, green and blue emission with a CIE coordinate of (0.30, 0.44), a peak current efficiency of 4.75cd/A and a high luminance of 4206cd/m(2). Displays based on the developed white QLEDs exhibit a wide color gamut of 114% NTSC. This work confirms the effectiveness of the proposed ZnMgO/PEDOT:PSS ICL and the feasibility of making all-solution processed tandem white QLEDs by using the proposed ICL.