Effect of sandwiched YbCl3layer thickness on exciton dynamics of Yb3+doped CsPbCl3perovskite photodetectors.

Yb3+doped CsPbCl3metal halide perovskite photodetectors (PDs) in the structure of CsPbCl3(50 nm)/YbCl3(xnm)/CsPbCl3(50 nm), in whichxranges from 10 to 40 nm corresponding to the molar ratio from 6.3% to 25.2%, are fabricated by thermal evaporation on Si/SiO2substrate. Photoresponse from 350 to 980 nm have been achieved with the optimal responsivity (R) of 3959, 5425, 955 A W-1for the case of 20 nm YbCl3at the wavelength (λ) of 420, 680 and 980 nm, respectively. A series of photophysical and electrical characterization has been performed and it is found that the remarkably improved photoresponse originates from the combining effects of upconversion and defects passivation from Yb3+. Moreover, the optimal YbCl3thickness of 20 nm can be ascribed to the balance between upconversion and concentration quenching of Yb3+. The influence of the YbCl3doping on the CsPbCl3electronic structure is investigated and downshifting and stabilization of valence band maximum (VBM) can be attributed to the p-type doping and counteracting effect of Yb3+and Cl-, respectively.

Exciton dynamics and photoresponse behavior of thein situannealed CsSnBr3perovskite films synthesized by thermal evaporation.

The CsSnBr3photodetectors are fabricated by thermal evaporation and 75 °Cin situannealing, and the effect ofin situannealing on the morphology, structure, exciton dynamics and photoresponse of thermally evaporated CsSnBr3films are investigated. Especially, temperature dependent steady-state photoluminescence (PL) and transient PL decaying have been analyzed in details for understanding the exciton dynamics. Meanwhile, effect of annealing on the activation energy for trap sites (Ea), exciton binding energy (Eb), activation energy for interfacial trapped carriers (ΔE), trap densities and carriers mobilities are studied and the annealed (A-CsSnBr3) reveals obviously lowerEband trap density together with notably higher carrier mobility than those of the unannealed (UA-CsSnBr3). Temperature dependence of the integrated PL intensity can be ascribed to the combining effect of the exciton dissociation, exciton quenching through trap sites and thermal activation of trapped carriers. The temperature dependent transient PL decaying analysis indicates that the PL decaying mechanism at low and high temperature is totally different from that in intermediate temperature range, in which combing effect of free exciton and localized state exciton decaying prevail. The beneficial effects of thein situannealing on the photoresponse performance of the CsSnBr3films can be demonstrated by the remarkable enhancement of the optimal responsivity (R) afterin situannealing which increases from less than 1 A W-1to 1350 A W-1as well as dramatically improved noise equivalent power, specific detectivityD* and Gain (G).

Imidazo[1,2-b]pyridazine as Building Blocks for Host Materials for High-Performance Red-Phosphorescent Organic Light-Emitting Devices.

A novel electron-transporting unit, imidazo [1,2-b]pyridazine (IP), was first reported for developing host materials. The IP moiety possesses excellent electron-transporting ability and great thermal stability. Using carbazole as p-type units and IP as n-type units, several bipolar host materials, namely, IP6Cz, IP68Cz, IP36Cz, and IP368Cz, were developed through altering the substitution site of the IP core. Among these four materials, 6-site-substituted IP6Cz and 6,8-site-substituted IP68Cz exhibit the best electroluminescence (EL) performance. IP6Cz- and IP68Cz-based red phosphorescent organic light-emitting diodes using Ir(pq)2acac as the emitter exhibit extremely high EL efficiency with the maximum external quantum efficiency (ηext,max) of 26.9 and 25.2% and an insignificant efficiency roll-off. Moreover, IP6Cz- and IP68Cz-based deep-red devices doped by Ir(piq)2acac also show satisfactory EL performance with a ηext,max of 20.5 and 19.9%, respectively. The influence of different substitution sites of the IP core on the photophysical and electrochemical properties was systematically investigated. This study demonstrates that IP could be a first-rate electron-transporting unit for bipolar materials for red-emitting devices.

Effects of Au nanoparticles and ZnO morphology on the photocatalytic performance of Au doped ZnO/TiO2 films.

Au doped ZnO nanocomposite films on TiO2 seeding layer (AuZ/T) were fabricated by hydrothermal processing and their photocatalytic performance was investigated. It could be found that the AuZ/T with micrometer(µm)-sized, lying ZnO bulks revealed optimal photocatalytic performance toward methyl orange under simulated sunlight, whose apparent degradation rate constant K app of 1.31 was about 20% higher compared to that of ZnO/TiO2 and 3 times higher compared to that of ZnO. The Au nanoparticles, TiO2 seeding layer and hydrothermal processing time imposed vital influence on the morphology of ZnO nanostructures, which played key roles in the formation of ZnO/TiO2 heterojunction and charge transfer (CT) inside it, as demonstrated by kinetics of transient photoluminescence (PL) decaying. The incorporation of Au nanoparticles not only induced the variations of ZnO crystallinity and reduction of ZnO band gap (E g), but also generated the Schottky heterojunction of metal-semiconductor, which would be beneficial to the CT inside nanocomposite films and separation of photo-generated electron-hole pairs, as verified by the remarkable PL suppression. The mechanism responsible for photocatalysis enhancement, which was resulted from the hybrid effects of Au nanoparticles and the ZnO morphology was discussed in details.

[1,2,4]Triazolo[1,5- a]pyridine-Based Host Materials for Green Phosphorescent and Delayed-Fluorescence OLEDs with Low Efficiency Roll-Off.

Herein, a series of universal bipolar host materials, 9,9'-([1,2,4]triazolo[1,5- a]pyridine-2,6-diylbis(4,1-phenylene))bis(9 H-carbazole) (TP26Cz1), 3-(2-(4-(9 H-carbazol-9-yl)phenyl)-[1,2,4]triazolo[1,5- a] pyridine-6-yl)-9-phenyl-9 H-carbazole (TP26Cz2), 9,9'-([1,2,4]triazolo[1,5- a]pyridine-2,7-diylbis(4,1-phenylene))bis(9 H-carbazole) (TP27Cz1), and 3-(2-(4-(9 H-carbazol-9-yl)phenyl)-[1,2,4]triazolo[1,5- a]pyridin-7-yl)-9-phenyl-9 H-carbazole (TP27Cz2), using [1,2,4]triazolo[1,5- a]pyridine (TP) as electron-transporting moiety and carbazole as hole-transporting moiety, were designed and synthesized. All four compounds possess remarkable carrier-transporting properties and excellent thermal stability with high glass-transition temperature ( Tg) in the range of 136-144 °C. The hole- and electron-transporting abilities could be regulated by adjusting the linkage mode between the carbazole and TP units, and balanced charge-transporting properties were realized in TP26Cz2 and TP27Cz2. The phosphorescent and thermally activated delayed-fluorescence (TADF) organic light-emitting diodes (OLEDs) based on these host materials exhibit superior performance with high efficiency and low roll-off. For example, TP26Cz2-hosted phosphorescent OLED (PhOLED) exhibits the maximum external quantum efficiency (ηext) of 25.6%, and at the high luminance of 5000 cd m-2, the ηext still remained at 25.2%. TP27Cz1-hosted TADF device exhibits the maximum ηext of 15.5% and only dropped to 15.4% at the luminance of 1000 cd m-2. Moreover, the influence of linking mode of carbazole unit and TP units in these hosts on their photophysical and carrier-transporting properties as well as the electroluminescence (EL) performance of devices was discussed.

Photocatalytic Performance of 3D Ni/Graphene/ZnO Composites Fabricated by Hydrothermal Processing.

ZnO nanorods are fabricated by the hydrothermal processing on the 3 dimensional (3D) Ni/Chemical Vapor Deposition (CVD) grown multilayer graphene and 3D Ni foams, respectively, and their photocatalytic performance are investigated. It is found that the composites with the graphene sandwiched between the 3D Ni and ZnO nanorods with 4 hours hydrothermal growth exhibits superior photocatalytic performance toward methyl orange (MO) under simulated sunlight, whose apparent degradation rate constant is about 1.3 times larger compared to that without graphene incorporated. Meanwhile, the underlying substrates show tremendous influence on the morphology and structures of ZnO nanorods, which imposes vital influence on the composites photocatalytic performance. The sparsely distributed and well crystalized ZnO flower-like nanorods with the enhanced content ratio of (002) plane on the 3D Ni/graphene foam reveal optimal performance, which can be attributed to the hybrid effect of the effective separation of the photo-generated electron-hole pairs due to the easy transferring of charges at graphene/ZnO interface through secure graphene/ZnO contacts, and the enhanced photocatalytic reduction of well crystallized and (002) enriched ZnO nanorods. The mechanism responsible for the enhancement of the photocatalytic degradation and the formation of the distinguished morphology and structure of ZnO nanorods are discussed in details.

[1,2,4]Triazolo[1,5-a]pyridine as Building Blocks for Universal Host Materials for High-Performance Red, Green, Blue and White Phosphorescent Organic Light-Emitting Devices.

The electron-accepting [1,2,4]triazolo[1,5-a]pyridine (TP) moiety was introduced to build bipolar host materials for the first time, and two host materials based on this TP acceptor and carbazole donor, namely, 9,9'-(2-([1,2,4]triazolo[1,5-a]pyridin-2-yl)-1,3-phenylene)bis(9H-carbazole) (o-CzTP) and 9,9'-(5-([1,2,4]triazolo[1,5-a]pyridin-2-yl)-1,3-phenylene)bis(9H-carbazole) (m-CzTP), were designed and synthesized. These two TP-based host materials possess a high triplet energy (>2.9 eV) and appropriate highest occupied molecular orbital/lowest unoccupied molecular orbital levels as well as the bipolar transporting feature, which permits their applicability as universal host materials in multicolor phosphorescent organic light-emitting devices (PhOLEDs). Blue, green, and red PhOLEDs based on o-CzTP and m-CzTP with the same device configuration all show high efficiencies and low efficiency roll-off. The devices hosted by o-CzTP exhibit maximum external quantum efficiencies (ηext) of 27.1, 25.0, and 15.8% for blue, green, and red light emitting, respectively, which are comparable with the best electroluminescene performance reported for FIrpic-based blue, Ir(ppy)3-based green, and Ir(pq)2(acac)-based red PhOLEDs equipped with a single-component host. The white PhOLEDs based on the o-CzTP host and three lumophors containing red, green, and blue emitting layers were fabricated with the same device structure, which exhibit a maximum current efficiency and ηc of 40.4 cd/A and 17.8%, respectively, with the color rendering index value of 75.

Dependence of the Nitrogen Dioxide (NO2) Sensitivity of SnO(x) -Sn/Graphene Gas Sensors on Vacuum Annealing and Ultraviolet (UV) Ozone Exposure.

Tin oxides and tin (SnO(x) -Sn) compound films were thermally evaporated onto chemical vapor deposition (CVD)-grown graphene films to obtain improved nitrogen dioxide (NO2) gas sensitivity. The effects of the vacuum annealing and ultraviolet (UV) ozone (O3) exposure of the bare graphene films prior to the thermal evaporation on the SnO(x) -Sn films' sensitivities, bonding states, and surface morphologies were investigated. With increasing annealing time, the coverage of the SnO(x) -Sn nanoparticles on the graphene increased and the p to n sensitivity transition occurred when n-type SnO(x) -Sn nanoparticles became dominant instead of the p-type graphene films for sensors without O3 exposure. Meanwhile, the opposite p-type sensitivity response was dominant with increasing annealing time for the O3-treated sensors. The chemisorbed Sn on the graphene generated by O3 exposure was oxidized by highly reactive NO2, resulting in a p-type doping effect, which would lead to n- to p-type sensitivity transition when the hole concentration exceeded the initial electron concentration of the n-type SnO(x) -Sn compound films. Vacuum annealing and O3 exposure also exhibited a tremendous influence on the SnO(x) -Sn films' surface morphologies, which could be responsible for the subsequent sensitivity dependence.