Blended host ink for solution processing high performance phosphorescent OLEDs.

In order to solve the interface issues in solution deposition of multilayer OLED devices, a blended host concept was developed and applied to both spin-coating and inkjet printing of phosphorescent OLEDs. The blended host consists of 1,3-bis(carbazolyl)benzene (mCP) and1,3,5-tri(phenyl-2-benzimidazoly)-benzene (TPBi). Maximum current efficiency (CE) of 24.2 cd A-1 and external quantum efficiency (EQE) of 7.0% have been achieved for spin-coated device. Maximum CE and EQE of 23.0 cd A-1 and 6.7% have been achieved for inkjet printed device. The films deposited by printing and spin-casting were further researched to explore the effect of those different processing methods on device performance.

The Influence of Materials, Heterostructure, and Orientation for Nanohybrids on Photocatalytic Activity.

In this work, different structures based on electrodeposited n-type ZnO nanorods and p-type Cu2O, CuSCN, and NiO nanostructures are fabricated for the degradation of methyl orange (MO). The influence of materials, heterostructure, and orientation for nanohybrids on photocatalytic activity is discussed for the first time. The heterojunction structures show remarkable enhancement compared to the bare semiconductor. The morphology of nanostructure has mainly an influence on the photocatalytic activity. NiO has the highest catalytic activity among the four pristine semiconductor nanostructures of ZnO, Cu2O, CuSCN, and NiO. The greatest enhancement of the photocatalytic activity is obtained using a ZnO/NiO (1 min) heterostructure attributed to the heterojunction structure and extremely higher specific surface area, which can degrade MO (20 mg/L) into colorless within 20 min with the fastest photocatalytic speed among homogeneous heterojunction structures. Meanwhile, the methodology and data analysis described herein will serve as an effective approach for the design of hybrid nanostructures for solar energy application, and the appropriate nanohybrids will have significant potential to solve the environment and energy issues.

Organic Upconversion Display with an over 100% Photon-to-photon Upconversion Efficiency and a Simple Pixelless Device Structure.

Compared to traditional near-infrared (NIR) imaging devices, NIR-to-visible upconversion displays, which integrated a NIR photodetector with a visible light-emitting diode, have merits of simple device structure, low cost, high resolution, and a simple pixelless structure. However, photon-to-photon upconversion efficiencies of these devices are typically much lower than unity. Here we report an all-organic NIR-to-visible upconversion display with a photon-to-photon upconversion efficiency higher than 100% by integrating a photomultiplying organic NIR photodetector with a high-efficiency thermally activated delayed fluorescent organic light-emitting diode. To the best of our knowledge, this is the first report showing a photon-to-photon upconversion efficiency over 100% without using a built-in transistor for current amplification.

Electronic Level Alignment at an Indium Tin Oxide/PbI2 Interface and Its Applications for Organic Electronic Devices.

The electronic level alignment at the indium tin oxide (ITO)/PbI2 interface is investigated by an ultraviolet photoelectron spectroscopy. An n-type conductivity property is found for PbI2 as well as a downward shift energy level at the ITO/PbI2 interface. These indicate that PbI2 can be used as an anode buffer layer for organic electronic devices. The power conversion efficiency of the organic solar cell based on tetraphenyldibenzoperiflanthene/C70 planar heterojunction is dramatically increased from 1.05 to 3.82%. Meanwhile, the thermally activated delayed fluorescence organic light-emitting diode based on 4,4',4″-tri( N-carbazolyl)triphenylamine-((1,3,5-triazine-2,4,6-triyl)tris(benzene-3,1-diyl))tris(diphenylphosphine oxide) shows a significantly reduced turn-on voltage and enhanced power efficiency from 6.26 to 18.60 lm/W. The improved performance is attributed to the high hole injection/extraction efficiency at the ITO/PbI2 interface. Besides, the near-infrared (NIR) absorption of lead phthalocyanine (PbPc)-based NIR organic photodetector (NIR-OPD) is dramatically increased, indicating that the PbI2 layer can also be used as a template layer for the growth of the triclinic phase of PbPc. As a result, the optimized device shows an external quantum efficiency of 26.7% and a detectivity of 9.96 × 1011 jones at 900 nm, which are among the highest ones reported for organic NIR-OPDs.

Highly Controllable and Efficient Synthesis of Mixed-Halide CsPbX3 (X = Cl, Br, I) Perovskite QDs toward the Tunability of Entire Visible Light.

CsPbX3 (X = Cl, Br, I) perovskite quantum dots (PQDs) have been intensively investigated on photoelectric devices due to their superior optical properties. To date, the stability of CsPbX3 PQDs is still an open challenge. The previous mixed-halide CsPbX3 PQDs were generally obtained via the anion-exchange method at 40 °C. Here, the single- and mixed-halide CsPbX3 PQDs are synthesized at high temperature via the hot injection technique. The surface ligands could thus be strongly coordinated onto the surface of the PQDs, which dramatically improve the optical properties of the PQDs. The resulting CsPbX3 PQDs have high quantum yield (QY, 40-95%), narrow full width at half-maximum (FWHM) (the narrowest FWHM <10 nm), tunable band gap (408-694 nm), and highly strong photostability. The variation of their emission peaks upon anion atoms is well-supported by the theoretical band gaps calculated by the density functional theory calculations with the alloy formula correction. Hence, these PQDs show great potential as good candidates for photoelectric devices.

Interface Engineering of Organic Schottky Barrier Solar Cells and Its Application in Enhancing Performances of Planar Heterojunction Solar Cells.

In this work, we describe the performance of organic Schottky barrier solar cells with the structure of ITO/molybdenum oxide (MoOx)/boron subphthalocyanine chloride (SubPc)/bathophenanthroline (BPhen)/Al. The SubPc-based Schottky barrier solar cells exhibited a short-circuit current density (Jsc) of 2.59 mA/cm(2), an open-circuit voltage (Voc) of 1.06 V, and a power conversion efficiency (PCE) of 0.82% under simulated AM1.5 G solar illumination at 100 mW/cm(2). Device performance was substantially enhanced by simply inserting thin organic hole transport material into the interface of MoOx and SubPc. The optimized devices realized a 180% increase in PCE of 2.30% and a peak Voc as high as 1.45 V was observed. We found that the improvement is due to the exciton and electron blocking effect of the interlayer and its thickness plays a vital role in balancing charge separation and suppressing quenching effect. Moreover, applying such interface engineering into MoOx/SubPc/C60 based planar heterojunction cells substantially enhanced the PCE of the device by 44%, from 3.48% to 5.03%. Finally, we also investigated the requirements of the interface material for Schottky barrier modification.

Highly efficient organic tandem solar cell with a SubPc interlayer based on TAPC:C70 bulk heterojunction.

We report a small molecule tandem organic photovoltaic (OPV) cell with a high power conversion efficiency (PCE) of 7.27%. This cell contains two subcells with an identical mixed active layer of C70:5 wt%TAPC (1,1-bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane). The performance was dramatically improved by simply inserting a thin boron subphthalocyanine chloride (SubPc) interlayer, which results in an increase of the short-circuit current and open-circuit voltage as well as a decrease of the series resistance of the tandem cell. The response of the cell only contributed from the absorption of C70. The high PCE was attributed to the high absorption efficiency of C70 and improved holes extraction efficiency at the anode due to the band bending occurs at both MoO3/SubPc and SubPc/C70:5 wt%TAPC interfaces.

Recyclable Magnetic Mesoporous Nanocomposite with Improved Sensing Performance toward Nitrite.

A magnetic nanomaterial for nitrite ion detection was demonstrated in the present study. This nanomaterial was prepared by grafting a rhodamine 6G derivative (denoted as Rh 6G-OH) into the channels of core-shell magnetic mesoporous silica nanospheres. The nanocomposite (denoted as Fe3O4@Rh 6G) showed large surface area and improved fluorescent performance to accumulate and recognize NO2(-), and its superparamagnetic behavior played an important role in reusability. The fluorescent intensity decreased linearly along with the NO2(-) concentration in the range of 1-50 µM, and the detection limit was estimated to be 0.8 µM, which was much lower than the maximum limit of nitrite ion in drinking water (65 µM) recommended by World Health Organization. Importantly, Fe3O4@Rh 6G could be magnetically collected and effectively reutilized after six test cycles.

Highly efficient red OLEDs using DCJTB as the dopant and delayed fluorescent exciplex as the host.

In this manuscript, we demonstrated a highly efficient DCJTB emission with delayed fluorescent exciplex TCTA:3P-T2T as the host. For the 1.0% DCJTB doped concentration, a maximum luminance, current efficiency, power efficiency and EQE of 22,767 cd m(-2), 22.7 cd A(-1), 21.5 lm W(-1) and 10.15% were achieved, respectively. The device performance is the best compared to either red OLEDs with traditional fluorescent emitter or traditional red phosphor of Ir(piq)3 doped into CBP host. The extraction of so high efficiency can be explained as the efficient triplet excitons up-conversion of TCTA:3P-T2T and the energy transfer from exciplex host singlet state to DCJTB singlet state.

Efficient and stable planar heterojunction perovskite solar cells with an MoO3/PEDOT:PSS hole transporting layer.

A solution processed MoO3/PEDOT:PSS bilayer structure is used as the hole transporting layer to improve the efficiency and stability of planar heterojunction perovskite solar cells. Increased hole extraction efficiency and restrained erosion of ITO by PEDOT: PSS are demonstrated in the optimized device due to the incorporation of an MoO3 layer.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant.

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.

High-performance organic small-molecule panchromatic photodetectors.

High-performance panchromatic organic photodetectors (OPDs) containing small molecules lead phthalocyanine (PbPc) and C70 fullerene as donor and acceptor, respectively, were demonstrated. The OPDs had either a PbPc/C70 planar heterojunction (PHJ) or a PbPc/PbPc:C70/C70 hybrid planar-mixed molecular heterojunction (PM-HJ) structure. Both the PHJ and the PM-HJ devices showed a broad-band response that covered wavelengths from 300 to 1100 nm. An external quantum efficiency (EQE) higher than 10% and detectivity on the order of 10(12) Jones were obtained in the wavelength region from 400 to 900 nm for the PHJ device. The EQE in the near-infrared region was enhanced by using the PM-HJ device structure, and a maximum EQE of 30.2% at 890 nm was observed for the optimized device with a 5% PbPc-doped C70 layer. Such an EQE is the highest at this wavelength of reported OPDs. The detectivity of the PM-HJ devices was also higher than that of the PHJ one, which is attributed to the increased efficiency of exciton dissociation in bulk heterojunction structure, increased absorption efficiency caused by formation of triclinic PbPc in the PbPc:C70 mixed film when it was deposited on a pristine PbPc layer, and high hole mobility of the PbPc-doped C70 layer.

Efficient triplet application in exciplex delayed-fluorescence OLEDs using a reverse intersystem crossing mechanism based on a ΔES-T of around zero.

We demonstrate highly efficient exciplex delayed-fluorescence organic light-emitting diodes (OLEDs) in which 4,4',4″-tris[3-methylphenyl(phenyl)aminotriphenylamine (m-MTDATA) and 4,7-diphenyl-1,10-phenanthroline (Bphen) were selected as donor and acceptor components, respectively. Our m-MTDATA:Bphen exciplex electroluminescence (EL) mechanism is based on reverse intersystem crossing (RISC) from the triplet to singlet excited states. As a result, an external quantum efficiency (EQE) of 7.79% at 10 mA/cm(2) was observed, which increases by 3.2 and 1.5 times over that reported in Nat. Photonics 2012, 6, 253 and Appl. Phys. Lett. 2012, 101, 023306, respectively. The high EQE would be attributed to a very easy RISC process because the energy difference between the singlet and triplet excited states is almost around zero. The verdict was proven by photoluminescence (PL) rate analysis at different temperatures and time-resolved spectral analysis. Besides, the study of the transient PL process indicates that the presence of an unbalanced charge in exciplex EL devices is responsible for the low EQE and high-efficiency roll-off. When the exciplex devices were placed in a 100 mT magnetic field, the permanently positive magnetoelectroluminescence and magnetoconductivity were observed. The magnetic properties confirm that the efficient exciplex EL only originates from delayed fluorescence via RISC processes but is not related to the triplet-triplet annihilation process.

Enhanced performances in inverted small molecule solar cells by Ag nanoparticles.

We demonstrate a highly efficient inverted small molecular solar cell with integration of Ag nanoparticles (NPs) into the devices. The optimized device based on thermal evaporated Ag NPs provides a power conversion efficiency (PCE) of 4.87%, which offers 33% improvement than that of the reference device without Ag NPs. Such a high efficiency is mainly attributed to the improved electrical properties by virtue of the modification of the surface of ITO with Ag NPs and the enhanced light harvesting due to localized surface plasmon resonance (LSPR). The more detail enhanced mechanism of the PCE by introduction of Ag NPs is also discussed.

Surface plasmon enhanced organic solar cells with a MoO3 buffer layer.

High-efficiency surface plasmon enhanced 1,1-bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane:C70 small molecular bulk heterojunction organic solar cells with a MoO3 anode buffer layer have been demonstrated. The optimized device based on thermal evaporated Ag nanoparticles (NPs) shows a power conversion efficiency of 5.42%, which is 17% higher than the reference device. The improvement is attributed to both the enhanced conductivity and increased absorption due to the near-field enhancement of the localized surface plasmon resonance of Ag NPs.

The influence of type-I and type-II triplet multiple quantum well structure on white organic light-emitting diodes.

We demonstrate high-efficient white organic light-emitting diodes (WOLEDs) based on triplet multiple quantum well (MQW) structure and focus on the influence on WOLEDs through employing different potential barrier materials to form type-I and type-II MQWs, respectively. It is found that type-I MQW structure WOLEDs based on 1,3,5-tris(N-phenyl-benzimidazol-2-yl)benzene as potential barrier layer (PBL) offers high electroluminescent (EL) performance. That is to say, maximum current efficiency and power efficiency are achieved at about 1,000 cd/m2 with 16.4 cd/A and 8.3 lm/W, which increase by 53.3% and 50.9% over traditional three-layer structure WOLEDs, respectively, and a maximum luminance of 17,700 cd/m2 is earned simultaneously. The achievement of high EL performance would be attributed to uniform distribution and better confinement of carriers within the emitting layer (EML). However, when 4,7-diphenyl-1,10-phenanthroline or 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline is used as PBL to form type-II MQW structure, poor EL performance is obtained. We attribute that to improper energy level alignment between the interface of EML/PBL, which leads to incomplete confinement and low recombination efficiency of carriers, a more detailed mechanism was argued.

Ultraviolet-ozone-treated PEDOT:PSS as anode buffer layer for organic solar cells.

Ultraviolet-ozone-treated poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)was used as the anode buffer layer in copper phthalocyanine (CuPc)/fullerene-based solar cells. The power conversion efficiency of the cells with appropriated UV-ozone treatment was found to increase about 20% compared to the reference cell. The improved performance is attributed to the increased work function of the PEDOT:PSS layer, which improves the contact condition between PEDOT:PSS and CuPc, hence increasing the extraction efficiency of the photogenerated holes and decreasing the recombination probability of holes and electrons in the active organic layers.

Hybrid polymer/ZnO solar cells sensitized by PbS quantum dots.

Poly[2-methoxy-5-(2-ethylhexyloxy-p-phenylenevinylene)]/ZnO nanorod hybrid solar cells consisting of PbS quantum dots [QDs] prepared by a chemical bath deposition method were fabricated. An optimum coating of the QDs on the ZnO nanorods could strongly improve the performance of the solar cells. A maximum power conversion efficiency of 0.42% was achieved for the PbS QDs' sensitive solar cell coated by 4 cycles, which was increased almost five times compared with the solar cell without using PbS QDs. The improved efficiency is attributed to the cascade structure formed by the PbS QD coating, which results in enhanced open-circuit voltage and exciton dissociation efficiency.

Very broad white-emission spectrum based organic light-emitting diodes by four exciplex emission bands.

White light is emitted by an organic light-emitting diode by inserting two blend layers of m-MTDATA:Al(DBM)(3) and TPD:Bphen between an m-MTDATA hole-transporting layer and a Bphen electron-transporting layer, where m-MTDATA, TPD, Al(DBM)(3), and Bphen are 4,4('),4('')-tris[methylpheny(phenyl)amino]-triphenylamine, N,N(')-bis(3-methylphenyl)-N,N(')-diphenylbenzidine, tris(dibenzoyl methane)-aluminum, and 4,7-diphenyl-1,10-phenanthroline molecules, respectively. The white-light spectrum consists of four broad bands that arise from blue-emitting TPD/Bphen, green-emitting m-MTDATA/Bphen, orange-emitting TPD/Al(DBM)(3), and red-emitting m-MTDATA/Al(DBM)(3) exciplexes, respectively, and strongly overlap at 400-760 nm. Any monomer emission is not generated. A high-color rendering index of 94.1, Commission Internationale de l'Eclairage-1931(x,y) coordinates of (0.33, 0.35), and correlated color temperature of 5477 K were obtained at 10 V. Discussion is given for the formation mechanism of the four exciplexes.

Lighting object-based nondoped-type white organic light-emitting diode with N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-benzidine)-4,4'-diamine as the chromaticity-tuning layer.

We demonstrate a nondoped white organic light-emitting diode in which the blue, green, and red emissions are generated from 4,4(')-bis(2,2(')-diphenylvinyl)-1,1(')-biphenyl, tris(8-hydroxyquinoline)aluminum, and a submonolayer of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7- tetramethyl-julolidyl 9-enyl)-4H-pyran layers, respectively. A thin layer of N,N(')-diphenyl-N,N(')-bis(1-naphthyl)(1,1(')-benzidine)-4,4(')-diamine (NPB), which differed from the traditional hole-transporting layer, was introduced into the device. The thickness of this thin NPB layer was changed to tune the chromaticity and optimize the white color quality. The white device with a 3 nm chromaticity-tuning NPB layer gives the Commission Internationale de l'Eclairage-1931 xy coordinate of (0.327, 0.336), a color rendering index of 90.2, a maximum luminance of 19,096 cd/m(2), and a maximum current efficiency of 4.12 cd/A. The electroluminescence mechanism of the white device was also discussed.