The polarity of zinc oxide nanostructures is crucial to modern electronic devices in terms of electrical and optical properties. However, it is still unclear whether the growth direction which affects the polarity of zinc oxide nanorods in hydrothermal processes is Zn-, O- or mix-polar. Earlier studies suggested that it should be Zn-polar based on thermodynamic calculations. Later studies proposed that the nanorods are O-polar, i.e. less stable than Zn-polar, resulting in the formation of nanotubes by KOH etching. Recently, the possibility of the co-existence of both Zn- and O-polar has been demonstrated. Therefore, we investigated the polarity issue by fabricating two types of ZnO nanorods under acidic and alkaline growth conditions. The as-grown and etched morphologies of these two types of nanorods are obviously different. Valence band X-ray photoemission spectroscopy (VB-XPS) has been employed to determine the polarity. We found that nanorods from both conditions are Zn-polar. This led us to find out that the formation of nanotubes is determined by the surface energy on the Zn-polar face of heterogeneously grown nanorods. The surface energy of ZnO nanorods can be controlled by a second acidic chemical bath, as long as the surface is not annealed. Furthermore, the thermodynamics of the process was studied to investigate the possible growth mechanism after the confirmation of polarity.

Anion exchange reaction is a particularly versatile tool for the synthesis of a large class of nanomaterials. Here we report a low temperature, fast, reversible anion exchange reaction in halide perovskite thin film. Although processed in the solid-state phase, the exchanged hybrid perovskite shows good quality in terms of morphology conservation, phase transformation, and homogeneous composition. The easily exchanged reaction during the crystallization process suggests the robust nature of the Pb–CH3NH3 framework and high diffusion ability of halide ions in the perovskite lattice. Furthermore, we show its application in perovskite solar cells; we find that the anion exchange reaction does not induce any remarkable defects resulting from the lattice transformation and morphology reconstruction. In some case, the beneficial exchange of halide species involving simultaneous displacement reaction and crystallization can be used to improve the perovskite solar cell performance. Our work provides new physical insight into understanding the perovskite formation mechanism and the ionic behavior in the perovskite.

Two new iridium(III) cyclometallated complexes (1 and 2) based on the 2-(1-phenoxy-4-phenyl)-5-methylpyridine ligand have been developed. By attaching a flexible phenoxy group on the phenyl ring of 2-phenylpyridine (Hppy), the light-emitting properties of the resulting IrIII complexes have been improved, while the introduction of an electron-donating methyl group on the pyridyl ring of Hppy can keep the triplet emission in the green region by compensating for the reduced energy gap caused by the phenoxy group. Owing to the unique electronic structures induced by the ligand, the vacuum-evaporated organic light-emitting devices (OLEDs) of the type [ITO/NPB (40 nm)/(1 or 2):CBP (20 nm)/BCP (10 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (100 nm)] furnished peak OLED efficiencies at 10.0%, 31.1 cd A−1 and 14.5 lm W−1 for 1 and 11.7%, 38.1 cd A−1 and 31.8 lm W−1 for 2. By replacing the electron-injection/electron-transporting materials (BCP and Alq3) with TPBi, the green-emitting devices based on 1 gave outstanding peak efficiencies at 22.5%, 76.2 cd A−1 and 72.8 lm W−1. Extremely high peak efficiencies of 24.5%, 84.6 cd A−1 and 77.6 lm W−1 were even obtained for the 2-doped devices and both of them are superior in performance to the benchmark dopants Ir(ppy)3 and Ir(ppy)2(acac). Moreover, polymer light-emitting devices were also fabricated using 1 and 2via the spin-coating method, and their device performances are characterized by 14.4%, 39.5 cd A−1 and 12.4 lm W−1 for 1 and 12.6%, 29.6 cd A−1 and 18.1 lm W−1 for 2. When 2 was used to make three-color white-light OLEDs, respectable device efficiencies of 15.3 cd A−1, 7.5% and 9.1 lm W−1 were achieved and their white color CIE coordinates are improved relative to Ir(ppy)3.

4,4′-bis(1,2,2-triphenylvinyl)biphenyl (BTPE) nanowires have been facilely grown by either post-annealing its vacuum-sublimed amorphous film or slowly evaporating its chloroform solution. The morphology and density of the nanowires can be easily tuned by changing the growth conditions. For example, isolated single nanowires were readily obtained by thermally depositing the BTPE on a heated substrate, while bundles of nanotubes can be achieved by slowly evaporating a droplet of the BTPE solution. The self-assembled BTPE nanowires show enhanced and blue-shifted photoluminescence compared with that of its amorphous film. The nanowires exhibit a highly hydrophobic surface with a water contact angle of 126°. Also, the BTPE nanowires scatter the light effectively due to the random orientation of the wires. By depositing the BTPE nanowires on the backside of the glass substrate as a scattering media for organic light-emitting diodes, a 31.5% efficiency improvement has been achieved.Graphical abstractHighlights► Various BTPE nanostructures have been facilely fabricated by dry or wet processing. ► BTPE nanowires show higher, bluer PL emission, lower wettability and stronger scattering ability. ► A 31.5% efficiency improvement was achieved with BTPE nanowires as scattering media for OLEDs.

To make a full color organic electroluminescent display, conventionally it requires three fine metal shadow masks (FMM) to pattern the red, green and blue light-emitting layer. In this work, by arranging the blue light-emitting layer as a shared layer for all sub-pixels, we demonstrate that a full color display can be achieved by two FMM processes, thus reducing one FMM process compared to conventional method. The red, green and blue sub-pixels can be optimized independently despite the reduction of one FMM process. Also, the performance of the red and green sub-pixels is not degraded by the shared blue light-emitting layer. Due to elimination of one FMM, the process TACT time, mask cost and alignment error can all be reduced, thus cutting down the manufacturing cost of full color organic electroluminescent display.Graphical abstractTo make a full color organic electroluminescent display, conventionally it requires three fine metal shadow masks (FMM) to pattern the red, green and blue light-emitting layer (a). However, we show that by arranging the blue light-emitting layer as a shared layer for all sub-pixels, a full color display can be achieved by two FMM processes, thus reducing one FMM process compared to conventional method (b).Highlights► We reduce one fine shadow mask in the fabrication of full color OLED display. ► R, G, B pixels can be optimized independently despite the elimination of one mask. ► Performance of red, green and blue sub-pixels remains the same. ► Process TACT time, mask cost and alignment error can all be reduced.

We report top-emitting white organic light-emitting diodes (WOLEDs) by thermally evaporating non-doped (4-(4-(1,2,2-triphenylvinyl)phenyl)-7-(5-(4-(1,2,2-triphenylvinyl)phenyl)thiophen-2yl)benzo[c][1,2,5]thiadiazole) (BTPETTD) as a color conversion cap layer on top-emitting blue OLEDs. With a 240 nm cap layer, 74.5% of the blue photon energy are absorbed and converted to red emission with a conversion efficiency of 40%. By mixing the unabsorbed blue emission and red emission, the resulting top-emitting WOLEDs exhibit a broad band spectra with CIE coordinates of (0.34, 0.35), high color stability over a wide range of driving voltages, and peak efficiency of 17.7 cd/A and 8.7 lm/W.Graphical abstractResearch highlights► Top-emitting WOLEDs capped with a color conversion layer have been demonstrated. ► The top-emitting WOLEDs exhibit ultra high color stability over a wide range of driving voltages. ► It is easy to fabricate such top-emitting WOLEDs. ► With 240 nm color conversion layer, the top-emitting WOLEDs exhibit a CIE coordinates of (0.34,0.35), peak efficiency of 17.7 cd/A and 8.7 lm/W.

It is challenging to obtain broadband emission spectra in top-emitting white organic light-emitting diodes (WOLEDs) due to the well known microcavity effects. In this work, we demonstrate that the microcavity effects can be greatly alleviated by employing a low reflection tri-cathode-layer Yb (5 nm)/Au (15 nm)/MoO3 (35 nm). Top-emitting WOLEDs with evenly separated red, green and blue emission peaks have been achieved. The white emission spectra show weak angle dependence as well. At a luminance of 1000 cd/m2, the top-emitting WOLEDs show an efficiency of 23 cd/A, 10.5 lm/W, a 1931 Commission International de L’Eclairage coordinate of (0.36, 0.42) and a high color rendering index of 85. The top-emitting WOLEDs have been successfully applied in the Si based microdisplay.Graphical abstractHighlights► Microcavity effects have been greatly alleviated by a low reflection cathode. ► The low reflection cathode consist of Yb (5 nm)/Au (15 nm)/MoO3 (35 nm). ► Top-emitting WOLEDs with evenly separated R, G, B peaks have been obtained. ► At 1000 cd/m2, efficiency of 23 cd/A, CIE (0.36, 0.42) and CRI 85 were achieved. ► Top-emitting WOLEDs have been successfully applied in the Si based microdisplay.

High brightness and efficient white stacked organic light-emitting diodes have been fabricated by connecting individual blue and red emissive units with the anode–cathode layer (ACL) consisting of LiF (1 nm)/Ca (25 nm)/Ag (15 nm). Use 1,3-bis(carbazol-9-yl)benzene (mCP):bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III (FirPic) as the blue emitter and tris(8-hydroxy-quinolinato)aluminium (Alq3):4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) as the red emitter, white light emission with CIE coordinates of (0.32, 0.38) was obtained at a driving voltage of 26 V with a luminance of 40,000 cd/m2. By replacing the red fluorescent emitter with a phosphorescent one, the color coordinates were improved to (0.33, 0.31). The peak external quantum efficiency was enhanced from 5.3% (at 28.2 mA/cm2) to 10.5% (at 1.4 mA/cm2) as well.

We present in this paper new design and optimization techniques for polarization interference filters (PIF). PIF can be used in liquid crystal on silicon projection systems for color separation and recombination. The technique introduced is based on a new Jones matrix formulation, and real time spectral output simulations for rapid convergence of design parameters. The case of a blue/yellow filter is given as an example.

Two new iridium(III) cyclometallated complexes (1 and 2) based on the 2-(1-phenoxy-4-phenyl)-5-methylpyridine ligand have been developed. By attaching a flexible phenoxy group on the phenyl ring of 2-phenylpyridine (Hppy), the light-emitting properties of the resulting IrIII complexes have been improved, while the introduction of an electron-donating methyl group on the pyridyl ring of Hppy can keep the triplet emission in the green region by compensating for the reduced energy gap caused by the phenoxy group. Owing to the unique electronic structures induced by the ligand, the vacuum-evaporated organic light-emitting devices (OLEDs) of the type [ITO/NPB (40 nm)/(1 or 2):CBP (20 nm)/BCP (10 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (100 nm)] furnished peak OLED efficiencies at 10.0%, 31.1 cd A−1 and 14.5 lm W−1 for 1 and 11.7%, 38.1 cd A−1 and 31.8 lm W−1 for 2. By replacing the electron-injection/electron-transporting materials (BCP and Alq3) with TPBi, the green-emitting devices based on 1 gave outstanding peak efficiencies at 22.5%, 76.2 cd A−1 and 72.8 lm W−1. Extremely high peak efficiencies of 24.5%, 84.6 cd A−1 and 77.6 lm W−1 were even obtained for the 2-doped devices and both of them are superior in performance to the benchmark dopants Ir(ppy)3 and Ir(ppy)2(acac). Moreover, polymer light-emitting devices were also fabricated using 1 and 2via the spin-coating method, and their device performances are characterized by 14.4%, 39.5 cd A−1 and 12.4 lm W−1 for 1 and 12.6%, 29.6 cd A−1 and 18.1 lm W−1 for 2. When 2 was used to make three-color white-light OLEDs, respectable device efficiencies of 15.3 cd A−1, 7.5% and 9.1 lm W−1 were achieved and their white color CIE coordinates are improved relative to Ir(ppy)3.