A new bipolar host material 2-(2′-(5-(dibenzo[b,d]furan-4-yl)-1H-indol-1-yl)-1,1′-biphenyl]-4-yl)-1-phenyl-1H-benzo[d]imidazole (INDY) has been designed and synthesized for solution-processed PHOLEDs. A hole-transporting indole conjugated dibenzofuran scaffold and an electron-transporting benzimidazole unit were orthogonally connected with incorporation of a 2,4′-biphenyl bridge, which endows a balanced bipolar charge transfer distribution and appropriate triplet energy level (>2.6 eV). The twisted conformation of INDY also ensures good thermal/morphological stability with high Tg (148 °C). The solution-processed green PHOLEDs achieved great device efficiencies with 27.33 cd/A and 12.26 lm/W at 7 V. Meanwhile, the red solution-processed PHOLEDs gained excellent performance with the maximum efficiencies of 17.20 cd/A, 9.82 lm/W, and 12.61%. In addition, all of the red devices presented excellent color stability with the same CIE coordinate as (0.65, 0.35) under varying dopant contents and operating voltages.Keywords: bipolar host material; high thermal stability; highly efficient; indole derivatives; phosphorescent OLEDs;

•Internal stress of diamond-like carbon (DLC) films is markedly reduced by N and Si co-doping.•Co-doping small amount of N is beneficial for reducing friction and wear of the films.•N and Si co-doped DLC films show low frictional sensitivity to air humidity.•CN groups act as electron accepter to reduce the activity of dangling bonds.Nitrogen and silicon co-incorporated DLC (N-Si-DLC) films were deposited by RF-CVD method, and the humidity effect on the tribological properties was investigated by a ball-on-disk type reciprocating tribometer in air environments at the relative humidity of 15, 45 and 75%. The chemical state of the elements and the bonding configurations were determined by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. Nano-indentation tests were performed to measure the hardness and modulus. The internal stress of the films was calculated by the Stoney equation. The characterization results showed that the N and Si contents were in the range of 4.4–10.3 at.% and 7.5–8.7 at.%, respectively. By co-doping N and Si, the internal stress of the films was reduced markedly, although with a slight reduction in the hardness and modulus. The N-Si-DLC films co-doped with a small amount of N exhibited lower friction and wear compared with the Si-DLC films without doping N. Also, these films showed low frictional sensitivity to the environmental humidity. The formation of CN and CN groups with strong electron withdrawing ability is thought to contribute to reducing the friction and wear, since they are strong electron acceptors which can reduce the electron density and nucleophilic reactivity of the dangling bonds formed on the film surface during sliding.

•Two novel indole-triazine based bipolar host materials were developed.•The meta-linking analog presented relatively high glass transition temperature of 124 °C.•PHOLEDs with the two host materials possess a high maximum external quantum efficiencies >14%.Two novel indole-based, bipolar, host materials were designed and synthesized by introducing the triazine unit to the 5-position of indole moiety with a meta-linking strategy. The two host materials exhibited excellence bipolar transport abilities and the meta-linking analog presented a high Tg value (>120 °C). Furthermore, their electrochemical and photo-physical properties were also fully characterized and all the results exhibited that the meta-linking strategy made a significant effect on the physical properties of the two hosts. Moreover, the PHOLED devices using 9-(4-(5-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-1H-indol-1-yl) phenyl)-9H-carbazole and 9-(4-(5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-1H-indol-1-yl)phenyl)-9H-carbazole as hosts were also fabricated to evaluate the practical utilities of host materials. The devices achieved the maximum external quantum efficiencies of 17.53% for para-linking compound and 14.53% for meta-linking analog, respectively. In particular, para-linking compound based device revealed the maximum external quantum efficiency was twice that of the device using 4,4′-bis(N-carbazolyl)-1,10-biphenyl as the host.

•Temperature-dependent device performance of a squaraine dye based OPV was studied.•Jsc, FF and PCE of the OPV cells increase with increasing the operating temperature.•Voc of the OPV cells decreases with increasing the operating temperature.We have systematically investigated the temperature-dependent device performance of organic photovoltaic (OPV) cells based on a squaraine dye. The 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine:[6,6]-phenyl C71 butyric acid methyl ester (DIBSQ:PC70BM) OPV devices were fabricated and characterized under 100 mW cm−2 (AM1.5G solar spectrum) in a temperature range from 285 to 360 K. The temperature-dependent photovoltaic parameters such as open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF) and power conversion efficiency (PCE) were studied in detail. The increasing temperature led to an improvement of Jsc and FF, which should be ascribed to the enhanced carrier mobilities and improved electrode/active layer contact thus the improvement of photocurrent extraction at an elevated temperature. However, the Voc decrease in the same period due to the carrier recombination of the OPV device. The increase in the Jsc and FF overtakes the decrease in the Voc with increasing temperature, resulting in a significantly improved PCE at elevated temperature. This study indicated that the DIBSQ based BHJ cells has promising potential for the practical application under changeable temperature environment.The temperature-dependent device performance of organic photovoltaic cells based on a squaraine dye has been systematically investigated.

Amorphous LaZnSnO thin films with different La doping concentration are prepared by a combustion solution process and the electrical performances of thin film transistors (TFTs) are investigated. The influence of La content on the structure, oxygen vacancies, optical and electrical performance of LaZnSnO thin films are investigated. At an appropriate amount of La doping (15 mol.%), LaZnSnO-TFT shows a superior electrical performance including a mobility of 4.2 cm2/V s, a subthreshold swing of 0.50 V/decade and an on/off current ratio of 1.9 × 107. The high performance LaZnSnO-TFT is attributed to the better interface between SiO2 and LaZnSnO channel layer and the suppression of oxygen vacancies by optimizing La content. It suggests that La doping can be a useful technique for fabricating high performance solution-processed oxide TFTs.

•ZnO:Al/Ag/ZnO:Al multilayer films prepared by sputtering.•ZnO:Al/Ag/ZnO:Al multilayer films used as source/drain electrode.•Improved performance of HfInZnO thin film transistors (TFTs) with the multilayer film.•Contact resistance of HfInZnO-TFTs calculated.We fabricated fully transparent hafnium indium zinc oxide (HfInZnO) thin film transistors (TFTs) with ZnO:Al(AZO)/Ag/ZnO:Al multilayer source/drain (S/D) electrodes. The effect of Ag interlayer thickness on the electrical and optical properties of AZO(60 nm)/Ag/AZO(60 nm) multilayer films was investigated. The AZO(60 nm)/Ag(10 nm)/AZO(60 nm) multilayer film shows a low sheet resistance of 10.5 Ω/square and a transmittance of 87%. Compared with HfInZnO-TFT with AZO electrode, the performance of the device with AZO/Ag/AZO multilayer electrode was significantly improved. The field effect mobility increased from 3.2 to 5.8 cm2/V s, and the threshold voltage reduced from 2.3 to 0.1 V. The improvement was attributed to the lower resistivity of AZO/Ag/AZO multilayer film. The result indicates that AZO/Ag/AZO multilayer electrode is a promising S/D electrode for fully transparent HfInZnO-TFTs.

We have fabricated novel BaZnSnO-TFT using a solution process and investigated the electrical performance and temperature stability. BaZnSnO-TFT shows an improved field-effect mobility of 3.2 cm2 V−1 s−1, a subthreshold swing of 0.61 V per decade and an on/off current ratio of 2 × 107 compared to those of ZnSnO-TFT. Density of state distribution of BaZnSnO and ZnSnO semiconductor has been extracted from electrical measurements. BaZnSnO-TFT shows an improved electrical performance and temperature stability due to smaller oxygen vacancies, less bulk trap density and interface state density.

•Double channel to fabricate HfInZnO thin film transistor (TFT)•Improvement in both mobility and negative bias stability of HfInZnO-TFTs•Capacitance–voltage method to analyze the trap charges and the doping density•Calculating the thickness of the induced channel layerWe investigate the electrical performance and negative bias stability of thin film transistors (TFTs) using double active layer. Double active layer is consisting of low oxygen content HfInZnO film as bottom channel and high oxygen content HfInZnO film as back channel. The HfInZnO-TFT with double channel layer shows a high mobility of 6.8 cm2/V s, a low threshold voltage of − 0.3 V, and a threshold voltage shifts of 0.65 V under − 20 V gate bias for 7200 s. The results suggest that HfInZnO with low oxygen content as the bottom channel could provide high carrier concentration and good HfInZnO/Al2O3 interface to improve field-effect mobility and negative bias stress stability. HfInZnO with high oxygen content as back channel can control the conductivity to reduce the off current of TFT. Thus, a double-active-layer structure is an effective way to improve the electrical performance of HfInZnO-TFT.

•Effect of copper sulfide (CuS) intermediate layers on the contact properties of GZO to p-GaN.•The contact mechanism analysis by XPS depth profile of p-GaN/CuS/GZO interfaces.•Effect of CuS intermediate layers on the performance of LEDs.•The epitaxy growth behavior of GZO films on CuS.Copper sulfide (CuS) was used as the intermediate layer to build ohmic contact of Ga-Doped ZnO (GZO) transparent conduction layer (TCL) to p-GaN. The CuS and GZO layers were prepared by thermal evaporation and RF magnetron sputtering, respectively. Although the GZO-only contacts to p-GaN exhibit nonlinear behavior, ohmic contact with a specific contact resistance of 1.6 × 10−2 Ω cm2 has been realized by inserting 3 nm CuS layer between GZO and p-GaN. The optical transmittance of CuS/GZO film was measured to be higher than 80% in the range of 450–600 nm wavelength. The possible mechanism for the ohmic contact behavior can be attributed to the increased hole concentration of p-GaN surface induced by CuS films after annealing. The forward voltage of LEDs with CuS/GZO TCL has been reduced by 1.7 V at 20 mA and the output power has been increased by 29.6% at 100 mA compared with LEDs without CuS interlayer. These results indicated that using CuS intermediate layer could be a potential ohmic contact method to realize high-efficiency LEDs.Graphical abstractCopper sulfide (CuS) was used as the intermediate layer to build ohmic contact of Ga-Doped ZnO (GZO) transparent conduction layer (TCL) to p-GaN.

In this paper, multi-chip LED modules with aluminum nitride (AlN), Al and aluminum oxide (Al2O3) based substrates were successfully designed, fabricated and investigated. Finite element method (FEM) and electrical test method were used to evaluate the thermal performance of LED modules. Both simulation and experimental results show that the module with AlN-based substrate exhibits better thermal performances than the two others. Moreover, AlN-based substrate LED module shows the best optical performances. The optical performances of the LED modules with different substrates not only verify that the optical output and degradation of LED has a direct relation with the input current, but also show that the degradation could begin earlier if the thermal dissipation is not managed well.

In this study, tribological and electrochemical performances of the new biomimetic synovial fluids were studied according to different composition concentrations, including hyaluronic acid, albumin and alendronic acid sodium. By using Taguchi method, the composition contents of the biomimetic synovial fluids were designed. Items such as friction coefficient, mean scar diameter and viscosity were investigated via a four-ball tribo-tester, viscosity meter and optical microscope. Polarization studies were carried out to analyze the electrochemical behaviour of the fluids. Results showed that hyaluronic acid dominates the viscosity of the fluids. High albumin concentration will reduce friction, while increasing wear rate due to the electrochemical effect. Alendronic acid sodium is found to reduce the biocorrosion of CoCrMo as well as provide better lubricating. In conclusion, biomimetic synovial fluids partially recover the functions of natural synovial fluids and provide good lubricating property.

Joint replacement is one of the most common and successful operations in orthopaedic surgery. It consists of replacing painful, arthritic, worn or cancerous parts of the joint with artificial surfaces shaped in such a way as to allow joint movement. The polyethylene component has been implicated as the key factor affecting the lifetime of these prostheses. This paper introduces a bionic artificial joint system which aims to prolong the lifetime of such prostheses. Included are bionic system design, investigation of bionic therapeutic lubricants and analysis of the mechanical properties of hip prostheses. Possible future developments which might improve artificial joints are also discussed.

New therapeutic bionic lubricants for artificial joint lubrication and the treatment of particle-induced osteolysis were developed. In this study, their tribological characteristics and mechanisms have been investigated. The tribological experimental results show that the therapeutic lubricants have the best anti-wear performance among the lubricants tested, such as hyaluronic acid (HA) and bovine serum. Some self-assembled membranes were found on the surfaces of the cups, which might contribute to the high lubrication performance of the therapeutic lubricants. The calculated film thickness of therapeutic lubricants is about 0.310 μm, which is still in the boundary lubrication region. The preliminary biological experiments show that therapeutic lubricants have good biocompatibility. It is necessary to do more experimental work in the future to investigate the formation of the membrane and the medical performance of the therapeutic bionic lubricants for better understanding of the effects of the undesired reactions induced by the wear debris.

A new bio-tribological simulator system was designed and built for basic wear tests on artificial hip joint materials and for common tribological studies applications. The module of hip joint simulator is consisted of Flexion and Extension (FE), Abduction and Adduction (AA) and Internal and External Rotation (IER). Preliminary tests were done with a 28 mm CoCrMo femoral head and a Ultra High Molecular Weight Polyethylene (UHMWPE) cup. Results showed that the wear rate was close to the clinical one. A frequency control system and a heating system were developed to offer a wide range of rotation frequency and temperature so as to provide proper experiments. In the Pin-on-Disk (POD) part, eight precision-made pins were generated and an advanced computer system was built up to measure the friction coefficient of the tests samples.