MoO3/Au/MoO3–PEDOT:PSS multilayer electrodes for ITO-free organic solar cells

The effect of the MoO₃–PEDOT:PSS composite layer in the MoO₃/Au/MoO₃–PEDOT:PSS multilayer electrode on the power conversion efficiency of ITO-free organic solar cells (OSCs) was evaluated. The MoO₃ (30 nm)/Au(12 nm)/MoO₃–PEDOT:PSS (30 nm)/PEDOT:PSS structure showed ~7% more optical transmittance than the MoO₃ (30 nm)/Au (12 nm)/MoO₃(30 nm)/PEDOT:PSS structure at 550 nm wavelength. The OSCs using MoO₃/Au/MoO₃–PEDOT:PSS multilayer electrodes as anodes showed a considerable improvement in power conversion efficiency (PCE), from 1.84% to 2.81%, comparable to ITO based OSCs with PCE of 2.89%. This improvement is attributed to the suppression of MoO₃ dissolution by the acidic hole transport layer (HTL) PEDOT:PSS on the MoO₃/Au/MoO₃–PEDOT:PSS multilayer electrode, resulting in high J_sc, V_oc and FF of the OSCs. This composite based multilayer electrode was shown to be a promising replacement in ITO-free flexible optoelectronic devices.     

A facile route for the preparation of organic bistable memory devices based on size-controlled conducting polypyrrole nanoparticles

Organic bistable memory devices (OBDs) with size-controlled polypyrrole (PPy) nanoparticles are developed by employing conducting PPy nanoparticle-embedded poly(vinyl alcohol) (PVA) as an active layer in OBDs. Monodisperse polypyrrole (PPy) nanoparticles with different diameters (20, 60, and 100 nm) are fabricated via dispersion polymerization in order to evaluate size-dependent bistable memory characteristics. Stable multilevel switching and a high on/off ratio over 100 were demonstrated with 20 nm of PPy in the OBDs.     

Highly efficient two component phosphorescent organic light-emitting diodes based on direct hole injection into dopant and gradient doping

A series of two component phosphorescent organic light-emitting diodes (PHOLEDs) combing the direct hole injection into dopant strategy with a gradient doping profile were demonstrated. The dopant, host, as well as molybdenum oxide (MoO₃)-modified indium tin oxide (ITO) anode were investigated. It is found that the devices ITO/MoO₃ (0 or 1 nm)/fac-tris(2-phenylpyridine)iridium [Ir(ppy)₃]:1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) (30 → 0 wt%, 105 nm)/LiF (1 nm)/Al (100 nm) show maximum external quantum efficiency (EQE) over 20%, which are comparable to multi-layered PHOLEDs. Moreover, the systematic variation of the host from TPBi to 4,7-diphenyl-1,10-phenanthroline (Bphen), dopant from Ir(ppy)₃ to bis(2-phenylpyridine)(acetylacetonate)iridium [Ir(ppy)₂(acac)], and anodes between ITO and ITO/MoO₃ indicates that balancing the charge as well as controlling the charge recombination zone play critical roles in the design of highly efficient two component PHOLEDs.     

Selective hydrogen sulfide (H2S) sensors based on molybdenum trioxide (MoO3) nanoparticle decorated reduced graphene oxide

This paper investigates a selective method of sensing hydrogen sulfide using molybdenum trioxide (MoO3) nanoparticle decorated graphene oxide (GO). Reduced graphene oxide was synthesized from natural graphite (NG) by the modified Hummer׳s method and decorated with the MoO₃ nanoparticles. Sensors were fabricated by the spin coating of MoO₃-decorated rGO between Pt electrodes on alumina substrate (Al₂O₃). In comparison with pristine rGO sensor, the MoO₃–rGO chemiresistors have a clear response to hydrogen sulfide down to 50 ppm at 70 °C. Thermal characterization of the sensor is studied. Results show that the fabricated devices have the maximum gas response at about 160 °C. Selectivity tests indicated that these sensors have poor respond to interfering analytes such as ethanol, carbon monoxide and nitric oxide. Furthermore, the effect of MoO₃ content and graphene oxide suspension concentration on the sensor response is investigated. Hereby it is shown that the sensor content of 3 wt% MoO₃ and of 5 mg/ml of GO suspension concentration has the highest sensitivity. Decorated reduced graphene oxide chemiresistors offer advantages such as remarkable potential for mass production due to their ease of manufacturing, good performance, and significant selectivity.     

P-type doping of organic wide band gap materials by transition metal oxides: A case-study on Molybdenum trioxide

A study on p-doping of organic wide band gap materials with Molybdenum trioxide using current transport measurements, ultraviolet photoelectron spectroscopy and inverse photoelectron spectroscopy is presented. When MoO₃ is co-evaporated with 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP), a significant increase in conductivity is observed, compared to intrinsic CBP thin films. This increase in conductivity is due to electron transfer from the highest occupied molecular orbital of the host molecules to very low lying unfilled states of embedded Mo₃O₉ clusters. The energy levels of these clusters are estimated by the energy levels of a neat MoO₃ thin film with a work function of 6.86 eV, an electron affinity of 6.7 eV and an ionization energy of 9.68 eV. The Fermi level of MoO₃-doped CBP and N,N′-bis(1-naphtyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (α-NPD) thin films rapidly shifts with increasing doping concentration towards the occupied states. Pinning of the Fermi level several 100 meV above the HOMO edge is observed for doping concentrations higher than 2 mol% and is explained in terms of a Gaussian density of HOMO states. We determine a relatively low dopant activation of ～0.5%, which is due to Coulomb-trapping of hole carriers at the ionized dopant sites.     

Low dark current inverted organic photodetectors employing MoOx:Al cathode interlayer

We report low dark current small molecule organic photodetectors (OPDs) with an inverted geometry for image sensor applications. Adopting a very thin MoO_x:Al cathode interlayer (CIL) in the inverted OPD with a reflective top electrode results in a remarkably low dark current density (J_d) of 5.6 nA/cm² at reverse bias of 3 V, while maintaining high external quantum efficiency (EQE) of 56.1% at visible wavelengths. The effectiveness of the CIL on the diode performance has been further identified by application to inverted OPDs with a semi-transparent top electrode, leading to a significantly low J_d of 0.25 nA/cm², moderately high EQE_{540 nm} of 25.8%, and subsequently high detectivity of 8.95 × 10¹² Jones at reverse bias of 3 V. Possible origins of reduced dark currents in the OPD by using the MoO_x:Al CIL are further described in terms of the change of interfacial energy barrier and surface morphology.     

Using metal/organic junction engineering to prepare an efficient organic base-modulation triode and its inverter

In this study, we investigated the influence of a buffer layer of molybdic oxide (MoO₃) at the metal/organic junction on the behavior of organic base-modulation triodes. The performance of devices featuring MoO₃/Al as the emitter electrode was enhanced relative to that of corresponding devices with Au and Ag, presumably because of the reduced in the contact barrier and the prevention of metal diffusion into the organic layer. The device exhibited an output current of ?16.1 μA at V_B = ?5 V and a current ON/OFF ratio of 10³. Using this architecture, we constructed resistance–load inverters that exhibited a calculated gain of 6.     

Aqueous solution-processed MoO3 as an effective interfacial layer in polymer/fullerene based organic solar cells

The authors demonstrate an effective anode interfacial layer based on aqueous solution-processed MoO₃ (sMoO₃) in poly (3-hexylthiophene) (P3HT) and indene-C60 bisadduct (ICBA) based bulk-heterojunction organic solar cells (PSCs). Various sMoO₃ concentration (0.03–0.25 wt%) was obtained by dissolving MoO₃ powder into deionized water directly with weak solubility. The characteristics of sMoO₃ films evaluated by atomic force microscope (AFM) and scanning electron microscope (SEM) suggest that the sMoO₃ films continuously cover the entire indium tin oxide (ITO) surface. The sMoO₃ based PSCs exhibit comparable power conversion efficiency with poly (3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT:PSS) based devices. However, even more importantly, the stability of sMoO₃ based devices have been greatly improved in air under continual light-illumination at 52 mW/cm². Further evaluations on Mo valence states and work function of sMoO₃ films by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) demonstrate that the aqueous solution-processed MoO₃ could act as an better anode interfacial layer than the conventional PEDOT:PSS.     

Fabrication of Bi2MoO6 nanoplates hybridized with g-C3N4 nanosheets as highly efficient visible light responsive heterojunction photocatalysts for Rhodamine B degradation

The Bi₂MoO₆/g-C₃N₄ heterojunction photocatalysts have been successfully fabricated using a simple liquid chemisorptions and thermal post-treatment. These nanostructured Bi₂MoO₆/g-C₃N₄ composites were extensively characterized by X-ray diffraction(XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR),UV–vis diffuse reflectance spectra (UV–vis DRS) and Photoluminescence (PL). The photocatalytic results show that 20 wt% Bi₂MoO₆/g-C₃N₄ sample exhibits efficient visible light activity and excellent photo-stability. The kinetic constant of RhB degradation over 20 wt% Bi₂MoO₆/g-C₃N₄ is about 5 and 2.5 times higher than that over pure Bi₂MoO₆ and g-C₃N₄ nanosheets, respectively. The enhanced photocatalytic performance is attributed to the construction of heterogeneous interface to promote photo-induced charge carrier pairs separation.     

Enhancing the short-circuit current,efficiency of inverted organic solar cells using tetra sulfonic copper phthalocyanine (TS-CuPc) as electron transporting layer

Efficient bulk-heterojunction polymer solar cells based on poly(3-hexylthiophene) (P3HT) blended with a fullerene derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were fabricated in inverted configuration by using copper phthalocyanine-3,4′,4′′,4′′′tetra-sulfonated acid tetrasodium salt (TS-CuPc) as the electron collecting layer and MoO₃ as hole collecting layer. TS-CuPc is observed to be critical for the device performance, significantly enhancing the Jsc and the PCE compared to devices based on TiOx. The optimal thicknesses of MoO₃ and TS-CuPc were 10 nm and 15 nm, respectively. Based on these optimal parameters, the PCE of 3.6% was obtained compared to 3.4% for the reference TiOx/P3HT:PCBM/MoO₃/Ag.     

Stable organic photovoltaic with PEDOT:PSS and MoOX mixture anode interfacial layer without encapsulation

Herein, we report about an efficient and stable organic photovoltaic that uses a poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and molybdenum oxide (MoO_X) mixture for the anode interfacial layer, and that can reach 4.43% power conversion efficiency (PCE) under AM1.5 conditions. Utilizing PEDOT:PSS:MoO_X (1:1), the shelf lifetime of poly(3-hexylthiophene) (P3HT), and indene-C₆₀ bisadduct (ICBA)-based solar cells without encapsulation, can be realized with only a 25% deterioration after 672 h of storage in air. Furthermore, we compare the photovoltaic performance of the P3HT:ICBA-based organic photovoltaic with PEDOT:PSS, and PEDOT:PSS:MoO_X, in which PEDOT:PSS:MoO_X has outperformed the others. In addition, the water vapor transmission rate of PEDOT:PSS:MoO_X is 0.17 gm/(m² day), which is much less than that of PEDOT:PSS.     

MoO3–Au composite interfacial layer for high efficiency and air-stable organic solar cells

Efficient and stable polymer bulk-heterojunction solar cells based on regioregular poly(3-hexylthiophene):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PC₆₁BM) blend active layer have been fabricated with a MoO₃–Au co-evaporation composite film as the anode interfacial layer (AIL). The optical and electrical properties of the composite MoO₃–Au film can be tuned by altering the concentration of Au. A composite film with 30% (weight ratio) Au was used as the AIL and showed a better performance than both pure MoO₃ and PEDOT:PSS as AIL. The surface morphology of the MoO₃–Au composite film was investigated by atomic force microscopy (AFM) and showed that the originally rough ITO substrate became smooth after depositing the composite film, with the root mean square roughness (RMS) decreased from 4.08 nm to 1.81 nm. The smooth surface reduced the bias-dependent carrier recombination, resulting in a large shunt resistance and thus improving the fill factor and efficiency of the devices. Additionally, the air stability of devices with different AILs (MoO₃–Au composite, MoO₃ and PEDOT:PSS) were studied and it was found that the MoO₃–Au composite layer remarkably improved the stability of the solar cells with shelf life-time enhanced by more than 3 and 40 times compared with pure MoO₃ layer and PEDOT:PSS layer, respectively. We argue that the stability improvement might be related with the defect states in MoO₃ component.     

Frequency and voltage dependency of interface states and series resistance in Al/SiO2/p-Si MOS structure

The capacitance–voltage (C–V) and conductance–voltage (G/ω–V) characteristics of Al/SiO₂/p-Si metal-oxide-semiconductor (MOS) Schottky diodes have been measured in the voltage range from ?3 to +3 V and frequency range from 5 KHz to 1 MHz at room temperature. It is found that both C and G/ω of the MOS capacitor are very sensitive to frequency. The fairly large frequency dispersion of C–V and G/ω–V characteristics can be interpreted in terms of the particular distribution of interface states at SiO₂/Si interface and the effect of series resistance. At relatively low frequencies, the interface states can follow an alternating current (AC) signal that contributes to excess capacitance and conductance. This leads to an anomalous peak of C–V curve in the depletion and accumulation regions. In addition, a peak at approximately ?0.2 V appears in the R_s–V profiles at low frequency. The peak values of the capacitance and conductance decrease with increasing frequency. The density distribution profile of interface state density (N_ss) obtained from C_HF–C_LF capacitance measurement also shows a peak in the depletion region.     

Facile synthesis and enhanced trimethylamine sensing performances of W-doped MoO3 nanobelts

The pure and W-doped MoO₃ nanobelts were prepared via a facile one-step hydrothermal method. The morphology and microstructure of the developed nanobelts were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The characterization results showed that as-prepared samples are uniform nanobelts with a mean length of 20 µm and width range of 100–200 nm, and W element was distributed uniformly in MoO₃ nanobelts. The comparison between pure and doped samples was carried out to reveal the superior gas sensing performance of W-doped MoO₃ nanobelts. The results of sensing properties indicate that the sensors based on W-doped MoO₃ nanobelts exhibit high response, good selectivity, and long term stability characteristics towards trimethylamine (TMA) gas, which are promising for trimethylamine sensors used to monitor air-quality and environmental.     

Solution-processed near-infrared polymer photodetectors with an inverted device structure

Solution-processed near-infrared polymer photodetectors with an inverted device structure were designed and fabricated. By introducing ZnO_x and MoO₃ as an electron extraction layer and a hole extraction layer, respectively, the asymmetric characteristics of the inverted polymer photodetectors was constructed. Operating at room temperature, the inverted polymer photodetectors exhibited the detectivity over 10¹² cm Hz^1/2/W from 400 to 850 nm, resulting from the enhanced photocurrent and reduced dark current induced by fabricating photoactive layer from solution with processing additive 1,8-diiodooctane. These device performances were comparable to those of inorganic counterparts.     

Effect of MoO42− partial substitution on optical enhancement of LaNa(MoO4)2:Dy3+ phosphors for white light emitting diodes

Dy³⁺ doped LaNa(MoO₄)₂ phosphors with different anionic groups (SO₄²⁻, PO₄³⁻ and BO₃³⁻) substitution were prepared through solid state reaction at 1100 °C. X-ray diffraction patterns of the as-prepared phosphors indicate that all samples have the standard LaNa(MoO₄)₂ structure. The photoluminescence spectra consist of a blue emission at 484 nm and a yellow emission at 576 nm, which corresponding to the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺ ions, respectively. The luminescence intensity of LaNa(MoO₄)_1.9(BO₃)_0.1:Dy³⁺, LaNa(MoO₄)_1.8(PO₄)_0.2:Dy³⁺ and LaNa(MoO₄)_1.9(SO₄)_0.1:Dy³⁺ phosphors are 2.8, 1.8 and 3-fold higher than that of LaNa(MoO₄)₂:Dy³⁺ phosphor, respectively. In addition, the luminescence lifetime values of LaNa(MoO₄)₂:Dy³⁺, LaNa(MoO₄)_2−x(BO₃)_x:Dy³⁺, LaNa(MoO₄)_2−x(PO₄)_x:Dy³⁺, and LaNa(MoO₄)_2−x(SO₄)_x:Dy³⁺ are 0.188, 0.189, 0.186 and 0.183 ms, respectively.     

Composite film of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and MoO3 as an efficient hole injection layer for polymer light-emitting diodes

We demonstrate improved performances in polymer light-emitting diodes (PLEDs) using a composite film of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and MoO₃ powder as a hole injection layer. The PLED with the composite film exhibits the current efficiency of 13.5 cd/A, driving voltage of 3.4 V, and half lifetime of 108.1 h, while those values of the PLED with a pristine PEDOT:PSS was 11.3 cd/A, 3.8 V, and 41.5 h, respectively. We also analyze the morphological, optical and electrical properties of the composite films by atomic force microscopy (AFM), UV–Vis-IR absorption, and ultraviolet photoemission spectroscopy (UPS). This work suggests that mixing MoO₃ into PEDOT:PSS is a simple and promising technique for use solution-based devices as an hole injection layer.     

Reduced contact resistance and highly stable operation in polymer thin-film transistor with aqueous MoOx solution contact treatment

We report on a newly developed solution process using MoO₃ for reducing source and drain (S/D) electrodes in organic thin-film transistor (TFT). By taking advantage of the difference in surface wettability between the gate dielectric layer and the S/D electrodes, the electrode treatment using the MoO_x solution was applied to polymer TFT with short channel lengths less than 10 μm. The contact resistance was noticeably reduced at the interface of the S/D electrodes in a polymer TFT using a pBTTT-C16. Furthermore, the field effect mobility for this TFT was enhanced from 0.03 to 0.1 cm²/V s. Most notably, the threshold voltage (V_th) shift under gated bias stress was less than 0.2 V after 10⁵ s, which is comparable to that of conventional poly crystalline Si TFT.     

Top illuminated organic photodetectors with dielectric/metal/dielectric transparent anode

The top illuminated organic photodetectors (OPDs) with a Dielectric/Metal/Dielectric (DMD) transparent anode are fabricated. The transparent electrode is composed of molybdenum trioxide (MoO₃)/silver (Ag)/MoO₃ layers and zinc oxide (ZnO)/aluminum (Al) is used for bottom cathode. The optimized DMD electrode has an optical transmittance of 85.7% at the wavelength of 546 nm and sheet resistance of ∼6 Ω/sq. The fabricated OPDs exhibit a high detectivity and wide range linearity.     

Influence of propyl alcohol addition during processing of molybdenum trioxide powders: Observation of novel dual-wavelength excitation photochromism

The novel dual-wavelength excitation photochromic molybdenum trioxide (MoO₃) powders are fabricated successfully via the hydrothermal method by the addition of propyl alcohol. The samples were fully characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis), and colorimetry. The characteristic spectrum of XRD demonstrates that the as-obtained products are highly pure. The results show that the flowerlike MoO₃ sample with the inducer of propyl alcohol has better photochromic properties, which was analyzed by colorimetry. It is shown that both of the samples exhibit a strong adsorption band between 250 and 400 nm in the UV range. Moreover, the UV–vis spectra shows that MoO₃ synthesized with added propyl alcohol absorbs light not only between 250 and 400 nm but also displays an additional band between 500 and 800 nm, demonstrating novel dual-wavelength excitation photochromic properties.