Artificial Dusk-Light Based on Organic Light Emitting Diodes

Abstract

We demonstrate the feasibility of bringing the sunset hue indoors via a dusk-light-style organic light emitting diode that exhibits a color temperature ranging between 1500 and 3000 K, covering that of sunset hue within the last 30 min before sunset. Like the sunset, the device chromaticity changes from yellowish white to reddish orange, with illuminance decreasing by 60-fold as the color temperature decreases from 2900 to 2100 K. The artificial dusk hue at 2745 K, for example, shows a 92 color rendering index with an 87% luminance spectrum resemblance with the sunset hue. The very high color rendering character is obtained by depositing phosphorescent red and yellow dyes in one emission layer and a fluorescent green dye doped into a fluorescent blue light emitting host in another, separated by a nanoscale carrier modulation interlayer to harvest the ultimate color rendering index and minimize the color temperature.

Novel Emitting System Based on a Multifunctional Bipolar Phosphor: An Effective Approach for Highly Efficient Warm‐White Light‐Emitting Devices with High Color‐Rendering Index at High Luminance

“…Meanwhile, the fluorescent (F) molecule Bepp 2 is used to generate blue singlet emission in the B–G layer and served as a host for sensitizing green emission, thereby achieving the broad white EL spectrum. An optimal management of B–G and G–OR layers aiming at balanced charge injection together with simultaneous efficient charge/exciton confinement, ensured this three‐color device possesses stable and high EL performance as follows: very high forward‐viewing EQE of 27.3% and PE of 74.5 lm W –1 at an illumination‐relevant luminance of 1000 cd m –2 with a high CRI of 85 and desirable eye‐friendly warm‐white[5c,10] Commission Internationale de L'Eclairage (CIE x , y ) coordinates of (0.43, 0.46) were realized, which maintained the high levels of 26.3% and 56.5 lm W −1 at 5000 cd m −2 , 24.3% and 45.8 lm W −1 at the extremely high luminance of 10 000 cd m −2 , with CRI in the range 86–87. To our knowledge, these values are competitive with, and even exceed, the best published data for a WOLED, simultaneously exhibiting a high efficiency and high CRI based on high luminance for the practical solid‐state lighting.…”

“…We have established that the devices reproducibly exhibit the high efficiencies reported, with stable CIE and CRI after continuous operation at a brightness of 1000 cd m −2 when driven at <4 V for 2–3 h without encapsulation. It should be noted that warm‐white light is especially desirable for comfortable ambient lighting that does not cause eye fatigue …”

OLEDs with Candle‐Like Emission

“…We continue to develop OLEDs with many (>3) emitters with ever-increasing spectrum frontline technology 24 Information Display 6/15 Fig. 1: Various light sources are shown along with their power and luminance spectra, SRI, CRI, and CCT.…”

Doping-free tandem white organic light-emitting diodes

“…Besides, to achieve high performance, the doping technology is required to tandem OLEDs, particularly for tandem WOLEDs (i.e., the pdoping and n-doping charge transport layers, doping differentcolor emitting layers (EMLs), doping CGLs) [13][14][15][16]. However, the doping technology may need (1) the controlment of codeposition rate and precise dopant concentration (i.e., 0.1%) in fabrication processes for both charge transport layers and EMLs, (2) the careful selection of hosts for different-color guests in EMLs, (3) the consideration of additional functional layers for both host and guest in EMLs, (4) the enhancement of cost for using hosts in EMLs [17][18][19][20]. Hence, tandem WOLEDs suffer from more sophisticated device engineering, longer fabrication time and higher cost.…”