Abstract
High light-quality and low color temperature are crucial to justify a comfortable healthy illumination. Wet-process enables electronic devices cost-effective fabrication feasibility. We present herein low color temperature, blue-emission hazards free organic light emitting diodes (OLEDs) with very-high light-quality indices, that with a single emissive layer spin-coated with multiple blackbody-radiation complementary dyes, namely deep-red, yellow, green and sky-blue. Specifically, an OLED with a 1,854 K color temperature showed a color rendering index (CRI) of 90 and a spectrum resemblance index (SRI) of 88, whose melatonin suppression sensitivity is only 3% relative to a reference blue light of 480 nm. Its maximum retina permissible exposure limit is 3,454 seconds at 100 lx, 11, 10 and 6 times longer and safer than the counterparts of compact fluorescent lamp (5,920 K), light emitting diode (5,500 K) and OLED (5,000 K). By incorporating a co-host, tris(4-carbazoyl-9-ylphenyl)amine (TCTA), the resulting OLED showed a current efficiency of 24.9 cd/A and an external quantum efficiency of 24.5% at 100 cd/m2. It exhibited ultra-high light quality with a CRI of 93 and an SRI of 92. These prove blue-hazard free, high quality and healthy OLED to be fabrication feasible via the easy-to-apply wet-processed single emissive layer with multiple emitters.
Highlights
Organic light-emitting diodes (OLEDs) have drawn enormous attention due to their increasing applications in flat-panel displays and solid state lightings[1,2,3,4]
For multiple emitters within a single emissive layer, for example, Xie et al reported a polymer organic light emitting diodes (OLEDs) with a color rendering index (CRI) of 92 and efficacy of 3.0 lm/W at 1,000 cd/m2, by incorporating wide-spectrum dopants[11]
We demonstrate wet-processed single emissive layer OLEDs which exhibit a low color temperature with very-high CRI and spectrum resemblance index (SRI) values, show less suppression of melatonin generation and eventually much friendlier to circadian rhythm, provide visual comfort to human eye, and show longer permissible exposure time to retina without causing any damage
Summary
Retinal exposure duration can be affected by color temperature and brightness of a light source, as can be seen in Fig. 2(a and b). At high voltage, Device B2 exhibited high efficiencies among all devices It is because a well optimize doping ratio managed to transfer energy from high band gap to low bandgap emitters, which caused increase in emission intensity in the long wavelength region (beyond 520 nm), as shown in electronic supplementary Figure S2 (b). The resulting OLED B2 exhibited high efficiencies than Device B1 and showed lower efficiency roll-off with increasing luminance, as shown in the electronic supplementary Figure S3(a). Of 0.7 wt.% Ir(ppy)3, 1.3 wt.% Ir(piq)2(acac) at fixed concentration of PO-01 (0.9 wt.%) and FIrpic (12 wt.%) It exhibits a PE of 14.5 lm/W, a CE of 25 cd/A and an EQE of 29.4% at 100 cd/m2, making which a very efficient single emissive layer based low color temperature wet-processed OLED31–33. It should be noted that Devices C1, C2 and C3 showed only a 20–25% decrease in CE and a 30–35% decrease in EQE from 100 to 1,000 cd/m2
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