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This study addressed the characteristics of electrolyte–insulator–semiconductor (EIS) pH sensors with array wells and sensing membrane stacks of 3-aminopropyltriethoxysilane (APTES)/SiO2. The arrays of square wells were fabricated by nanoimprint lithography (NIL) and investigated using an atomic force microscope (AFM). The surface chemical properties of molecular APTES on SiO2 were investigated by water contact angle (WCA) studies and X-ray photoelectron spectroscopy (XPS). The sensitivity, hysteresis, and drift of EIS sensors were studied. All of the sensing properties were greatly enhanced by using the techniques we propose. With these improvements, high-performance sensors can be fabricated for future biochemical applications.

In this study, the characteristics of ion-sensitive field-effect transistors (ISFETs) with silicon wire array channels and sensing membrane stacks of 3-aminopropyltriethoxysilane (APTES)/SiO2 were investigated. Si wires were fabricated by nanoimprint lithography and Si anisotropic/isotropic reactive-ion etching processes. The Si wires, with a line width of ∼200 nm, were undercut and nearly suspended, which formed an Ω -shape cross-section. The aspects of wires were investigated using an optical microscope, an atomic force microscope, a scanning electron microscope, and a transmission electron microscope. The sensitivity, hysteresis, and drift of ISFETs were investigated. The above sensing properties were all significantly improved with the proposed channels and the sensing membrane stacks. As such, high-performance ISFETs can be realized for future biochemical applications.

Abundant molecules enable countless combinations of device architecture that might achieve the desirable high efficiency from organic light-emitting diodes (OLEDs). Due to the relatively high cost of OLED materials and facilities, simulation approaches have become a must in further advancing the field faster and saver. We have demonstrated here the use of state-of-art simulation approaches to investigate the effect of molecular orbital energy levels on the recombination of excitons in OLED devices. The devices studied are composed of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) as hole transporting material (HTM), 4,4′-Bis(9-carbazolyl)-1,1′-biphenyl (CBP) as host, 2,2',2”-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) or bathophenanthroline (Bphen) as electron transporting materials. The outcomes reveal that exciton recombination highly sensitive to the energy-level alignment, injection barriers, and charge mobilities. A low energy-barrier (106 times greater than that in the TPBi based device. The high carrier mobility of Bphen whose electron mobility is 5.2 × 10−4 cm2 V−1 s−1 may lead to low charge accumulation and hence high exciton dynamics. The current study has successfully projected an in-depth analysis on the suitable energy-level alignments, which would further help to streamline future endeavours in developing efficient organic compounds and designing devices with superior performance.

Organic light-emitting diodes (OLEDs) have progressively attracted generous attention because of their versatile applications in solid state lighting and full color displays. High-efficiency is crucial for OLED devices being energy saving and to have a longer lifespan. Numerous approaches have been attempted to attain high-efficiency OLEDs via newly synthesized organic materials, light-extraction structure design and energy-efficient device architectures. The organic materials used in optoelectronic devices have inherently low dielectric constant. In this work, we demonstrate a comprehensive model to quantitatively investigate the role of dielectric constant of the electron transporting material on the electric field distribution, charge drift and exciton recombination probability across the emissive layer (EML) and electron transport layer (ETL) in organic light-emitting diode via commercialized electrical simulation package SETFOS.

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.

Solution processable hole transporting materials (HTMs) are indispensable component for the cost-effective and large-area roll-to-roll fabrication of organic light emitting diodes (OLEDs). Hole transport layers should display high triplet energy, good hole injection properties along with potential electron blocking capability. In this paper, we report a series of novel fluorene-based HTMs, 9,9-diethyl-2,7-bis(2-(trifluoromethyl)phenyl)-9H-fluorene (3), 9,9-diethyl-2,7-bis(3-(trifluoromethyl)phenyl)-9H-fluorene (4) and 9,9- diethyl-2,7-bis(4-(trifluoromethyl)phenyl)-9H-fluorene (5) containing symmetrical and asymmetrical substitution of trifluoromethyl pendants at different positions. The synthesized HTMs have an exceptional solubility in common organic solvents such as THF (tetrahydrofuran), o-Xylene, etc. and possess good thermal stability to form morphologically stable films. The suitable molecular energy level alignment (HOMO-LUMO) for barrier free injection, adequate ionization potential (6.12, 6.20, and 6.23 eV) and high triplet energies (3.12,3.17, and 3.13 eV) for compound 3, 4, and 5, these suitable characteristics promote materials performance as a good hole transporting layer (HTL). Solution-processed yellow phosphorescent OLEDs fabricated by utilizing these HTMs with a conventional yellow emitter Iridium (III)bis (4-phenylthieno [3,2-c]pyridinato-N,C2′)acetylacetonate (PO-01) doped in 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host. The best device with molecule 4 showed an improvement of 54 % in current efficiency (CE) from 23.3 to 35.8 cd/A and 14 % in external quantum efficiency (EQE) from 11.3 to 12.9 %, compared to reference device containing N, N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) as HTL. Compounds 3 and 5 based devices also showed a competitive performance with the reference device. The effect of solvent was also studied. These outcomes recommend that this type of solution processable HTMs will be promising contender for high-efficiency OLED devices.

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.

Candlelight-based, blue-hazard free lighting sources are friendly to the human eye and physiology, museum artifacts, ecosystems, the environment, and the night sky. Wet processing enables organic devices to be fabricated cost-effectively with a large area-size via continuous roll-to-roll manufacturing. We demonstrate here a candlelight organic light-emitting diode (OLED) using a wet process to deposit at least the layers of emission, hole-injection, and hole-transportation. The resulting 1918 K candlelight OLED is about 50 and 15 times safer to the retina and in terms of melatonin generation protection, respectively, as compared with the 5000 K white LED, CFL and OLED. It can reach a maximum brightness of 38 000 cd m−2, equivalent to 42 000 candlelight in one square meter, and its efficacy is 300 times that of candle and 3 times that of an incandescent bulb. This study may serve as a starting point to begin a healthy-light based “Lighting Renaissance” with feasible commercialization.

Precise optimization and modeling of electron-hole recombination probability in organic light-emitting diodes (OLEDs) are necessary for developing a comprehensive description of their functioning. High-performance organic materials, new device architecture and advanced processing technologies are developed to emerge the development of the OLED community. It is well acknowledged that electrical processes in the OLEDs include three key steps, i.e. charge injection, charge transport, and charge recombination. In this paper, we demonstrate a quantitative approach to investigate the effects of carrier mobility of electron transporting layer (ETL) on electric field and recombination profile across the organic layers of the device using software package SETFOS. The simulation outcomes proposed that a higher electron mobility results in a wider recombination zone in the desired emissive layer (EML), while narrower in case hole mobility is comparatively higher.

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

Electroluminescence-efficiency green emitter with both wet- and dry-process feasibility is highly desirable to realize cost-effective large roll-to-roll manufacturing and high performance products. We demonstrate here a wet- and dry-process feasible green bis[5-methyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one]iridium(picolinate) containing organic light-emitting diode device with an efficacy roll-up character between 100 and 1000 cd/m 2 . The newly synthesized iridium complex exhibits a relatively short excited-state lifetime (0.39 μs) and a high quantum yield of 74%, both which warrant this complex to be a highly electroluminescence active candidate. The wet processed device using a 3,5-di(9H-carbazol-9-yl) tetraphenylsilane host, for example, shows a 52 lm/W with an 18% external quantum efficiency (EQE) at 100 cd/m 2 , which increases to 61 lm/W with a 23% EQE at 1000 cd/m 2 . For the dry-processed device using a 4,4-bis(carbazol-9-yl)biphenyl host, it is 59 lm/W with a 25% EQE at 1000 cd/m 2 .

Light quality shows strong effects on humans in many aspects, including aesthetics, psychology, physiology, and health. By assuming that natural light has the best light quality, devising a pseudo-natural light is hence important and critical. Here, an all-weather pseudo-natural light is demonstrated based on a high number of broad-band emitters. By doping six broad-band organic light-emitting dyes in three separate emission layers, for example, the light source can exhibit a 92–96% similarity with the sunlight from dawn to dusk, and a color gamut of 80% in terms of NTSC. By combining six narrow-band light-emitting diodes (LEDs), a much wider gamut of 121% NTSC is achievable, but with a slightly poor daylight similarity, i.e., ranging between 80% and 83%. The daylight similarity, however, can easily be enhanced to at least 94% upon incorporating broad-band phosphors, even with the use of only one or two LEDs.

Organic light-emitting diode fabrication is suffering from extremely high material wasting during deposition especially using a typical point or even line source. Moreover, the need of depositing a high number of emitters and host(s) with a precise composition control in a single layer makes traditional vapor codeposition systems nearly impossible, unless otherwise with a very low yield. To improve, we have developed a novel thin-film deposition system with a planar source loadable with any premetered solvent-mixed organic compounds, plausibly with no component number limitation. We hence demonstrate experimentally, along with a Monte Carlo simulation, in the report the feasibility of using the technique to deposit on a large area-size substrate various organic materials with a relatively high material utilization rate coupling with high film uniformity. Specifically, nonuniformity of less than ±5% and material utilization rate of greater than 70% have been obtained for the studied films.

High efficiency green emission is crucial to the designs of energy-saving display and lighting. Efficient electroluminescent green emitters with both wet- and dry-process feasibility is highly desirable in order to realize, respectively, cost-effective large roll-to-roll manufacturing and high performance products. In this study, high-efficiency, phosphorescent, green organic light emitting diodes with a novel iridium complex, bis[5-methyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one] iridium (acetylacetonate), are demonstrated. They possess both wet- and dry-processing possibilities. The emitter exhibits a short excited-state lifetime, 1.25 μs, and a high quantum yield, 69%, due to the efficient intersystem crossing of the ground state to the excited state. Using 4,4′-bis(carbazol-9-yl)biphenyl as a host, the device shows at 1000 cd m−2 an external quantum efficiency (EQE) of 21% and power efficiency of 64 lm W−1 via vapor deposition, while 26% EQE and 69 lm W−1 by spin-coating, the highest among all reported wet-processed green organic light emitting diodes. Besides electroluminescence, the high device efficiency may also be attributed to the employed device architecture enabling therein an electron trap to facilitate the injection of this minor carrier against that of a hole, leading to a balanced carrier-injection, and hence a high carrier recombination and in turn a high device efficiency.

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.

The efficiency of highly efficient blue, green, red, and white organic light-emitting diodes (OLEDs) has been substantially advanced through the use of high surface-charge nanodots embedded in a nonemissive layer. For example, the blue OLED's markedly high initial power efficiency of 18.0 lm W(-1) at 100 cd m(-2) was doubled to 35.8 lm W(-1) when an amino-functionalized polymeric nanodot was employed. At high luminance, such as 1000 cd m(-2) used for illumination applications, the efficiency was improved from 12.4 to 21.2 lm W(-1), showing a significant enhancement of 71%. The incorporated highly charged nanodots are capable of effectively modulating the transportation of holes via a blocking or trapping mechanism, preventing excessive holes from entering the emissive layer and the resulting carrier-injection imbalance. Furthermore, in the presence of a high-repelling or dragging field arising from the highly charged nanodots, only those holes with sufficient energy are able to overcome the included barriers, causing them to penetrate deeper into the emissive layer. This penetration leads to carrier recombination over a wider region and results in a brighter emission and, therefore, higher efficiency.

We report the experimental observation and theoretical explanation of an unconventional interplay between divalent Co and trivalent Y dopants, both of which incur oxygen vacancies in the CeO2 host that has predominantly tetravalent Ce cations. The Co dopant atoms were experimentally found to act as a switch that turns on the dormant effect of Y-modulated band-gap reduction. As revealed by density functional theory (DFT) calculations with structures verified by synchrotron-radiation x-ray measurements, a Co 3d band that hybridizes with Ce 4f band was lowered due to reduced O 2p repulsion arising from oxygen vacancies incurred by Y doping and therefore gave rise to the observed band-gap narrowing effect. Such switch-and-modulator scheme for band-gap engineering in nanocrystal materials can lead to important applications in environmental protection and solar energy harvesting technologies.

Focus of the study has been placed on the effect of graphite content on tribological behavior of a Cu–Fe–C based friction material sliding against FC30 cast iron. Experimental results indicated that, after sintering in air, the densities of Cu–Fe–C specimens decreased, oxygen contents increased, and essentially all original metallic constituents turned into oxides. As graphite content increased, the amounts of Fe2O3 ,C u 2O and Cu–Sn decreased, while CuO and FeSn2 contents increased. The friction coefficient profiles of Cu–10%Steel wool–10%Al–10%Al2O3–10%Sn (vol%) material (C0) and Cu–10%Steel wool–10%C–10%Al–10%Al2O3–10%Sn (vol%) material (C10) are almost identical. After sliding for a few minutes, their friction coefficients start to decay. The friction coefficient of Cu–10%Steel wool–20%C–10%Al–10%Al2O3–10%Sn (vol%) material (C20) maintained to be high and stable throughout tests. The mass loss of C20 was larger than that of C0 or C10. The mass loss of FC30 sliding against C20 was smaller than that of FC30 sliding against C0 or C10. While both particulate and film types of debris were observed on each Cu–Fe–C specimen, more particulate debris was observed on C0 and C10 than on C20 surface. Chemical analysis of worn surfaces indicated that Fe was dominant on C0 and C10 surfaces, while large amounts of Fe and Cu were detected on the worn surfaces of both C20 and FC30.

This letter addresses the characteristics of polycrystalline-silicon (poly-Si) thin-film transistor (TFTs) with 3-D finlike channels fabricated using UV nanoimprint lithography. A transparent mold and poly-Si 3-D finlike channels with a line/space ratio of about 1:1 were fabricated and studied by SEM. The poly-Si TFTs with 3-D finlike channels, fabricated using a nanoimprint technique, have lower threshold voltage, higher ON/OFF current ratio, better subthreshold swing, higher field-effective mobility, and higher drain current than that with a single channel. The proposed approach can be utilized to fabricate high-performance poly-Si TFTs at low cost.

We report a novel solution-processable high molecule iridium complex, bis[5-methyl-7-trifluoro methyl-5H-enzo(c)(1,5)naphthyridin-6-one]iridium(picolinate) (CF3BNO), that exhibits a relatively short excited-state lifetime (0.30 μs) and extremely high quantum yield (95%). Current efficiency of 89.1 cd A−1 at 100 cd m−2 was obtained by using the CF3BNO complex to fabricate a blue-green light-emitting device.

The nanostructure of the light emissive layer (EL) of polymer light emitting diodes (PLEDs) was investigated using force modulation microscopy (FMM) and scanning time-of-flight secondary ion mass spectrometry (ToF-SIMS) excited with focused Bi(3)(2+) primary beam. Three-dimensional nanostructures were reconstructed from high resolution ToF-SIMS images acquired with different C(60)(+) sputtering times. The observed nanostructure is related to the efficiency of the PLED. In poly(9-vinyl-carbazole) (PVK) based EL, a high processing temperature (60 °C) yielded less nanoscale phase separation than a low processing temperature (30 °C). This nanostructure can be further suppressed by replacing the host polymer with poly[oxy(3-(9H-9-carbazol-9-ilmethyl-2-methyltrimethylene)] (SL74) and poly[3-(carbazol-9-ylmethyl)-3-methyloxetane] (RS12), which have similar chemical structures and energy levels as PVK. The device efficiency increases when the phase separation inside the EL is suppressed. While the spontaneous formation of a bicontinuous nanostructure inside the active layer is known to provide a path for charge carrier transportation and to be the key to highly efficient polymeric solar cells, these nanostructures are less efficient for trapping the carrier inside the EL and thus lower the power conversion efficiency of the PLED devices.

By using 10 kV C(60)(+) and 200 V Ar(+) ion co-sputtering, a crater was created on the light-emitting layer of phosphorescent polymer light-emitting diodes, which consisted of a poly(9-vinyl carbazole) (PVK) host doped with a 24 wt % iridium(III)bis[(4,6-difluorophenyl)pyridinato-N,C(2)] (FIrpic) guest. A force modulation microscope (FMM) was used to analyze the nanostructure at the flat slope near the edge of the crater. The three-dimensional distribution of PVK and FIrpic was determined based on the difference in their mechanical properties from FMM. It was found that significant phase separation occurred when the luminance layer was spin coated at 30 degrees C, and the phase-separated nanostructure provides a route for electron transportation using the guest-enriched phase. This does not generate excitons on the host, which would produce photons less effectively. On the other hand, a more homogeneous distribution of molecules was observed when the layer was spin coated at 60 degrees C. As a result, a 30% enhancement in device performance was observed.

Solution processable fullerene and copolymer bulk heterojunctions are widely used as the active layers of solar cells. In this work, scanning time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used to examine the distribution of [6,6]phenyl-C61-butyric acid methyl ester (PCBM) and regio-regular poly(3-hexylthiophene) (rrP3HT) that forms the bulk heterojunction. The planar phase separation of P3HT:PCBM is observed by ToF-SIMS imaging. The depth profile of the fragment distribution that reflects the molecular distribution is achieved by low energy Cs(+) ion sputtering. The depth profile clearly shows a vertical phase separation of P3HT:PCBM before annealing, and hence, the inverted device architecture is beneficial. After annealing, the phase segregation is suppressed, and the device efficiency is dramatically enhanced with a normal device structure. The 3D image is obtained by stacking the 2D ToF-SIMS images acquired at different sputtering times, and 50 nm features are clearly differentiated. The whole imaging process requires less than 2 h, making it both rapid and versatile.

Light-quality is extremely crucial for any light source to be used for illumination. However, a proper light-quality index is still missing although numerous electricity-driven lighting measures have been introduced since past 150 yr. We present in this communication a universal and easy-to-apply index for quantifying the quality of any given lighting source, which is based on direct comparison of its lumen spectrum with the natural light counterpart having the same color temperature. A general principle for creating high quality pseudo-natural light is accordingly derived. By using organic light-emitting diode technology, for example, daylight-style emission with a 96% natural light resemblance is obtained as a high number of organic emitters with diffused colors spanning throughout the entire visible range are employed. The same principle can be extended to other lighting technology such as light-emitting diode to generate natural light-style emission.

Highly efficient yellow organic light-emitting diodes (OLEDs) with a solution-process feasible emissive layer were fabricated by simply using molecular hosts doped with an iridium-complex based yellow emitter. The best yellow OLED device studied here showed for example, at 100 cd m−2, a power efficiency of 32 lm W−1, a 113% improvement compared with the prior record of 15 lm W−1 based on the same emitter with a polymeric host. The marked efficiency improvement may be attributed to the device being composed of an electron-injection-barrier free architecture, a device structure that led the excitons to generate preferably on the host to enable the efficiency-effective host-to-guest energy transfer to occur and the employed molecular host that exhibited a good host-to-guest energy transfer. The efficiencies were further improved to 53, 39 and 14 lm W−1 at 100, 1000 and 10 000 cd m−2, respectively, with the use of a micro-lens. This study also demonstrates the possibility of achieving relatively high device efficiency for wet-processed OLED devices via balancing the injection of carriers with commercially available OLED materials and limited designs in device structure.

We demonstrate the feasibility of using direct contact-printing in the fabrication of monochromatic and polychromatic organic light-emitting diodes (OLEDs). Bright devices with red, green, blue, and white contact-printed light-emitting layers with a respective maximum luminance of 29 000, 29 000, 4000, and 18 000 cd/m2 were obtained with sound film integrity by blending a polymeric host into a molecular host. For the red OLED as example, the maximum luminance was decreased from 29 000 to 5000 cd/m2 as only the polymeric host was used, or decreased to 7000 cd/m2 as only the molecular host was used. The markedly improved device performance achieved in the devices with blended hosts may be attributed to the employed polymeric host that contributed a good film-forming character, and the molecular host that contributed a good electroluminescence character.

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We report a high-efficiency blue organic light-emitting diode (OLED) with a solution-processed emissive layer composed of an oligomeric host of poly[3-(carbazol-9-ylmethyl)-3-methyloxetane] (PCMO) that possesses high triplet-energy and high electron mobility. The device exhibited a current efficiency of 40.4 cd A−1 with an external quantum efficiency (EQE) of 21.6% and power efficiency of 28.2 lm W−1 at 230 cd m−2 or 24.7 cd A−1, 10.3%, and 15.5 lm W−1 at 1 000 cd m−2. The high efficiency may be attributed to the host possessing a high electron mobility and lower electron injection barrier, resulting in a more balanced carrier-injection. Moreover, the high electron-mobility favors the transport of electrons, resulting in a more balanced carrier-injection in the emissive layer. The device efficiency has been further enhanced to 42.6 cd A−1 (22.9%, 29.7 lm W−1) at 124 cd m−2 or 28.8 cd A−1 (15.4%, 17.8 lm W−1) at 1 000 cd m−2 by pre-heating the emissive solution at an elevated temperature before spin-coating.

We present a solution-processed blue organic light-emitting diode (OLED) with markedly high current efficiency of 41.2 cd A−1 at 100 cd m−2 and 31.1 cd A−1 at 1000 cd m−2. The high efficiency was partly attributed to the use of a molecular host, 3,5-di(9H-carbazol-9-yl)tetraphenylsilane, which possesses a wide triplet band gap, high carrier mobility, ambipolar transport property and high glass transition temperature. Besides the intrinsically good physical properties, the solution-process also played an important role in fabricating the high-efficiency device, since it could make the molecular distribution of host and guest homogeneous in the emissive layer. Moreover, the device efficiency at higher brightness could be markedly enhanced by using an electron-blocking layer. As the microlens was introduced on the glass substrate to enhance the light outcoupling, the resultant device efficiency of the blue OLED further increased to 50.1 cd A−1 at 100 cd m−2 and 37.3 cd A−1 at 1000 cd m−2.

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We demonstrate a man-made lighting device of organic light-emitting diode (OLED) capable of yielding a sunlight-style illumination with various daylight chromaticities, whose color temperature ranges between 2300 and 8200 K, fully covering those of the entire daylight at different times and regions. The OLED employs a device architecture capable of simultaneously generating all the emissions required to form a series of daylight chromaticities. The wide color-temperature span may be attributed to that the recombination core therein can easily be shifted along the different emissive zones simply by varying the applied voltage via the use of a thin carrier-modulating layer.

The effects of process parameters on pattern embossing into hydrogen silsesquioxane films and the pattern degradation of hydrogen silsesquioxane were investigated. Methylisobutylketone (MIBK) was used to dilute hydrogen silsesquioxane, and NX-1000 (Nanonex) was used to imprint hydrogen silsesquioxane embossed with a Si grating mold at 25°–180°C under 2–2.5MPa. The imprint results were observed by scanning electron microscopy and correlated to the analysis results of Fourier transform infrared spectroscopy (FTIR) and nanoindentation. The FTIR results show that network-type bonding was promoted by dilution with MIBK and increasing baking temperatures from 50°Cto180°C. High-temperature thermal-cycle heat treatment can promote the formation of network bonds, which make hydrogen silsesquioxane film undergo plastic deformation more easily. In contrast, low-temperature thermal-cycle heat treatment can result in hydrogen silsesquioxane having a highly viscous response and high time-dependent deformation behavior....