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Long lifetime and high efficiency are strongly desired for electronic devices. Encapsulation is especially required for organic light-emitting diodes (OLEDs) because they are extremely sensitive to the ambient moisture and oxygen. However, few studies had investigated their individual effects. We found in this study that even with a trace amount, oxygen showed drastically marked effects on both the short- and long-term properties of OLEDs, either typical or tandem. It is unprecedented to see that moisture did not compromise the device performance at least within the 20 ppm level. In contrary, the moisture helped alleviate the attack of oxygen via reducing its kinetic energy and collision probability striking on the aluminum surface. The findings suggest a more stringent oxygen control in fabrication and encapsulation to achieve an upmost device performance.

Long exposure to intensive blue light may damage retina and suppress, at night, melatonin secretion. To devise a blue hazard-free light source with a long lifetime, we demonstrated here a tandem organic light-emitting diode (OLED) with candlelight-style emission, especially via the use of all commercially-available materials. The resultant device shows a color temperature of 1,500 K, significantly lower than the 1,800 K of oil lamps, 1,900 K of candles and 2,500 K of incandescent bulbs. It permits, at 100 lx, a retinal exposure-limit of 12 h, while merely 5 min for the 6,000 K cold-white LED or CFL. Notably, it is 15 times more human eye-friendly and 30% more melatonin generation-friendly than the candle. It shows a lifetime of 40,000 h at 1,000 candelas per meter square, which is about 20,000 times that of a candle and 40 times that of an incandescent bulb. It is 65 times more energy-saving as comparing with candles. Commercially viable human-friendly lighting can be expected in the near future to safeguard human health.

Long exposure to intensive blue light may damage retina and suppress, at night, melatonin secretion. To devise a blue hazard-free light source with a long lifetime, we demonstrated here a tandem organic light-emitting diode (OLED) with candlelight-style emission, especially via the use of all commercially-available materials. The resultant device shows a color temperature of 1500 K, significantly lower than the 1800 K of oil lamps, 1900 K of candles and 2500 K of incandescent bulbs. It permits, at 100 lx, a retinal exposure-limit of 12 h, while merely 5 min for the 6000 K cold-white LED or CFL. Notably, it is 15 times more human eye-friendly and 30 % more melatonin generation-friendly than the candle. It shows a lifetime of 40,000 h at 1000 cd per meter square, which is about 20,000 times that of a candle and 40 times that of an incandescent bulb. It is 65 times more energy-saving as comparing with candles. Commercially viable human-friendly lighting can be expected in the near future to safeguard human health.

We examined the performance of solution-processed organic light emitting diodes (OLEDs) by modifying the hole injection layer (HIL), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS). Atomic force microscopy (AFM) showed morphological changes with surface roughness (RRMS) of 1.47, 1.73, and 1.37 nm for pristine PEDOT: PSS, PEDOT: PSS modified with a 40 v% deionized water and with a 30 v% acetone, respectively. The surface hydrophobicity of the acetone modified PEDOT:PSS HIL layer was decreased by 34% as comparing with the water modified counterpart. Electrical conductivity was increased to two orders of magnitude for the water and acetone modified PEDOT:PSS as compared to pristine. We observed a low refractive index and high transmittance for the modified HILs. We fabricated and explored electroluminescent properties of bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) based sky blue device by utilizing HIL with and without modification. The changes in electrical conductivity, surface roughness, refractive index, and transmittance of the modified HILs strongly influenced the performance of devices. By utilizing a 30% acetone modified HIL, the power efficiency was increased from 14.2 to 24.2 lm/W, an increment of 70% and the EQE from 8.5 to 13.1% at 100 cd/m2, an increment of 54%. The maximum luminance also increased from 11,780 to 18,190 cd/m2. The findings revealed herein would be helpful in designing and fabricating high efficiency solution processed OLEDs.

Wet-process enables flexible, large area-size organic devices to be fabricated cost-effectively via roll-to-roll manufacturing. However, wet-processed devices often show comparatively poor performance due to the lack of solution-process feasible functional materials that exhibit robust mechanical properties. We demonstrate here a cross-linkable material, 3,6-bis(4-vinylphenyl)-9-ethylcarbazole (VPEC), to facilitate the injection of hole and meanwhile effectively confine electron to realize, for examples, high efficiency organic light-emitting diodes, especially at high luminance. The VPEC shows a hole mobility of 1 10

A bright high-efficiency host-free deep-blue organic light-emitting diode (OLED) is demonstrated. Without the aid of any carrier regulating layer, the deep-blue OLED shows a power efficiency of 1.7 lm W −1 with CIE coordinates of (0.143, 0.098) at 1000 cd m −2 . The respective power efficiency is increased from 1.7 to 2.1 and 2.2 lm W −1 as a single- and double-carrier regulating layers were incorporated. The respective peak luminance also increases from 5250 to 7620 and 9130 cd m −2 , an increment of 45% and 74%. The marked brightness improvement may be attributed to the incorporated carrier regulating layers that effectively lead carriers to recombine in a wider zone. Moreover, the blue emission can be hypsochromic shifted by varying the incorporation position of the carrier regulating layer and the emissive layer thickness.

Low color temperature (CT) lighting provides a warm and comfortable atmosphere and shows mild effect on melatonin suppression. A high-efficiency low CT organic light emitting diode can be easily fabricated by spin coating a single white emission layer. The resultant white device shows an external quantum efficiency (EQE) of 22.8% (34.9 lm/W) with CT 2860 K at 100 cd/m 2 , while is shown 18.8% (24.5 lm/W) at 1000 cd/m 2 . The high efficiency may be attributed to the use of electroluminescence efficient materials and the ambipolar-transport host. Besides, proper device architecture design enables excitons to form on the host and allows effective energy transfer from host to guest or from high triplet guest to low counterparts. By decreasing the doping concentration of blue dye in the white emission layer, the device exhibited an orange emission with a CT of 2280 K. An EQE improvement was observed for the device, whose EQE was 27.4% (38.8 lm/W) at 100 cd/m 2 and 20.4% (24.6 lm/W) at 1000 cd/m 2 .

Very-high color rendering index (CRI > 90) is extremely crucial for lighting in surgery, photography and exhibition of museums etc. We demonstrate herein an efficient very-high CRI organic light-emitting diode with CRI of 98 with an efficacy of 8.3 lm/W at 100 cd/m2, or CRI of 96 with 5.2 lm/W at 1000 cd/m2. The very high CRI may be attributed to the successful deposition and emission of the two full-spectrum complementary white emissive layers, especially as a thin interlayer is inserted in between to regulate the injection of carriers. Without the interlayer, the resultant CRI drops to 73 and efficacy to 3.6 lm/W at 1000 cd/m2. The employment of the carrier regulating layer also helps disperse the injected carriers, leading recombination to occur in a wider area and hence a higher efficiency.