The realization of solution-processed tandem quantum-dot LEDs (QLEDs) remains a technical challenge due to the limitations of inefficient interconnect layer and the damage caused by multiple solution processes. Here, we develop a high performance tandem QLED by face-to-face integrating a top-emitting QLED with a transparent QLED. The top and bottom units can be addressed independently, thereby enabling the tandem QLED to operate in series, parallel, and color-tunable modes for multifunctionality. In series mode, QLEDs demonstrate an ultra-low turn-on voltage of 3.3 V and a record-breaking external quantum efficiency of 60.7%. In parallel mode, QLEDs achieve an impressive brightness of over 4.8 × 10 6 cd m -2 . In color-tunable mode, the color, brightness, and color temperature can all be adjusted with a color tuning range of 114% NSTC. Moreover, both series and parallel connections contribute to an improved stability, resulting in a T 95 lifetime of nearly 30,000 h at 1000 cd m -2 , which is an improvement of approximately 2.8 times over control devices. Our work offers a feasible solution for achieving multifunctional tandem QLEDs with the advantages of solution processed, high efficiency, high brightness, long lifetime and full color tunability for various light source applications.
Group III–V semiconductor-based microscale light-emitting diode (micro-LED) displays are recognized as one of the most promising display technologies with superhigh brightness and resolution, strong contrast, and superlarge color gamut but currently suffer from low efficiency, low production yield, and high cost. Here, it is proposed to realize cost-effective and full-color micro-LED displays by using microscale perovskite quantum dot LEDs (micro-PeLEDs) as emitters. Bright and uniform red-, green-, and blue-emitting (RGB) micro-PeLED arrays with each pixel size as small as 45 µm are fabricated by in situ inkjet printing a perovskite quantum dot (PeQD) emissive layer in the structure of indium tin oxide/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/poly(9-vinylcarbazole) (PVK)/sodium dodecyl sulfate (SDS)/PeQD/1,3,5-tris(1-phenyl-1 H -benzimidazol-2-yl)benzene (TPBi)/LiF/Al. These RGB micro-PeLED arrays display an external quantum efficiency of 0.832%, 0.419%, and 0.052% for red, green, and blue colors, a resolution of 210 PPI, and a wide color gamut (135% of the National Television Standards Committee standard). The authors further demonstrate flexible and full-color active-matrix micro-PeLED displays, which have potential applications in future ultrahigh-definition displays, light communication, and artificial intelligence.
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