Color-pure green emission is essential to realize next-generation vivid displays. Recently, solution-processed OIHPs are attracting increasing attention because of their narrow emission, and potential to be fabricated energy-efficient and low-cost in lighting and display applications. However, the perovskite light emitting diodes (LEDs) that approach Rec. 2020 standard green emission with a maximum current efficiency ≥15 cd/A have not been achieved by far. Here, we present ultrapure green LEDs based on quantum confined colloidal perovskite emitters. A spin-coated thin film of two dimensional (2D) perovskites demonstrates a high absolute photoluminescence quantum efficiency (PLQE ~ 94%). The resultant perovskite LEDs show a maximum current efficiency >20 cd/A by using a composite emission layer of colloidal 2D perovskites and poly(methyl methacrylate). As compared to Rec. 2020 standard color gamut, the green emission shows >97% color saturation in the 1931 CIE color space. We present ultra-flexible perovskite LEDs with a bending curvature radius of 2 mm by using a 50 μm thin polyimide substrate. We further demonstrate a high-efficiency large-area (30 mm2) device without compromising in the device performance. These devices show ultimate potential to realize low-cost, large-scale fabrication of the ultra-pure green LEDs for the next-generation of displays.
Candles emit sensationally warm light with a very low color temperature, comparatively most suitable for use at night. In response to the need for such a human-friendly night light, we demonstrate the employment of a high number of candlelight complementary organic emitters to generate and mimic candlelight based on organic light emitting diode (OLED). One resultant candlelight style OLED shows a very-high color rendering index (CRI), with an efficacy at least 300 times that of a candle or at least two times that of an incandescent bulb. The device can be fabricated, for example, by using four candlelight complementary emitters: red, yellow, green, and sky-blue phosphorescent dyes. These dyes, in the present system, can be vacuum deposited into two emission layers that are separated by a nanolayer of carrier modulation material that is used to maximize very high CRI and energy efficiency. A nano carrier modulation layer also played a significant role in maintaining the low blue emission and high-red emission, the low color temperature of device was obtained. Importantly, a romantic sensation giving and supposedly physiologically friendly candlelight style emission can hence be driven by electricity in lieu of hydrocarbon burning and greenhouse gas-releasing candles that were invented 5000 years ago.
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