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Molybdenum ditelluride (MoTe2) has attracted ever-growing attention in recent years due to its novel characteristics in spintronics and phase-engineering, and an efficient and convenient method to achieve large-area high-quality film is an essential step toward electronic applications. However, the growth of large-area monolayer MoTe2 is challenging. Here, for the first time, we achieve the growth of a centimeter-sized monoclinic MoTe2 monolayer and manifest the mechanism of immobilized precursor particle driven growth. Microscopic characterizations reveal an obvious trend of immobilized precursor particles being consumed by the monolayer and continuing to provide a source for the growth of the monolayer. Time-of-flight secondary ion mass spectrometry verifies the attachment of hydroxide ions on the surface of the MoTe2 monolayer, thereby realizing the inhibition of crystal growth along the [001] zone axis and the continuous growth of the MoTe2 monolayer. The first-principles DFT calculations prove the mechanism of immobilized precursor particles and the absorption of hydroxide ions on the MoTe2 monolayer. The as-grown MoTe2 monolayer exhibits a surface roughness of 0.19 nm and average conductivity of 1.5 × 10-5 S/m, which prove the smoothness and uniformity of the MoTe2 monolayer. Temperature-dependent electrical measurements together with the transfer characteristic curves further demonstrate the typical semimetallic properties of monoclinic MoTe2. Our research elaborates the microscopic process of immobilized precursor particles to grow large-area MoTe2 monolayer and provides a new thinking about the growth of many other two-dimensional materials.

Defects easily form in organic-inorganic hybrid perovskite (CH3NH3PbX3) absorber layers acting as recombination centers which reduce the performance of solar cells. Therefore, defect passivation is an efficient method to improve the performance of solar cells. Herein, ethylamine alcohol chlorides is introduced into perovskite films to passivate defects. The hydroxyl group and ammonium group in ethylamine alcohol chlorides can interact with halogen in MAPbIxCl3-x to form hydrogen bonds suppressing ion migration. In addition, the crosslinking neighbouring perovskite grains through hydrogen bonds can also improve the perovskite grain size and film coverage. The data demonstrate that the obvious reduction of the defect concentration via defect passivation contributes to an enhancement of the open-circuit voltage from 0.87 V to 0.92 V and the device efficiency from 14.52% to 16.97%.

Interface strains and lattice distortion are inevitable issues during perovskite crystallization. Silane as a coupling agent is a popular connector to enhance the compatibility between inorganic and organic materials in semiconductor devices. Herein, a protonated amine silane coupling agent (PASCA-Br) interlayer between TiO2 and perovskite layers is adopted to directionally grasp both of them by forming the structural component of a lattice unit. The pillowy alkyl ammonium bromide terminals at the upper side of the interlayer provide well-matched growth sites for the perovskite, leading to mitigated interface strain and ensuing lattice distortion; meanwhile, its superior chemical compatibility presents an ideal effect on healing the under-coordinated Pb atoms and halogen vacancies of bare perovskite crystals. The PASCA-Br interlayer also serves as a mechanical buffer layer, inducing less cracked perovskite film when bending. The developed molecular-level flexible interlayer provides a promising interfacial engineering for perovskite solar cells and their flexible application.

Serious issues such as easy-oxidation of Sn2+, fast crystallization rate and high defect density are still existing in tin perovskites to restrain their photovoltaic performance. Herein, a strategy of bottom passivation by potassium thiocyanate (KSCN) has been developed in FA0.75MA0.25SnBrI2-based perovskite solar cells. KSCN interlayer exhibited multifunctional roles in aligning energy levels, assisting perovskite crystallization and promoting charge transport. The resulting champion device delivered superior power conversion efficiency (PCE) as high as 11.17% under AM 1.5G illumination. It is worth noting that the champion indoor photovoltaics efficiency under 2956 K@1062 lux (334.41 μW/cm2) illumination could approach 17.57%, which is the highest PCE for tin perovskite photovoltaics to our knowledge. The outstanding indoor performance demonstrates the huge application potential of eco-friendly tin perovskites.

Interface engineering is an efficient method for improving the performance of planar perovskite solar cells (PSCs). In this paper, the performance of PSCs was improved significantly by introducing 4,7-diphenyl-1,10-phenanthroline (Bphen) doped with bis(2-methyldibenzo-[f,h]quinoxaline) (Ir(MDQ)2(acac)) to modify the interface between perovskite (CH3NH3PbI3−xClx)/PCBM (phenyl-C61-butyric acid methyl ester) and an Ag electrode. The power conversion efficiency (PCE) was enhanced up to 15.87%, compared with 10.77% for the reference device without interlayer modification. It was found that the enhanced PCE was attributed to the better interface contact between the perovskite and Ag cathode. A suitable interface roughness is beneficial for reducing the leakage current and the probability of carrier recombination, resulting in an enhanced fill factor and thus improved device efficiency.

A new three-armed imidazolium phenoxy ionic liquid (TIPIL) has been successfully designed, synthesized and characterized. The thermal property, amorphous feature and ionic conductivity of TIPIL were also investigated. 1-Ethyl-3-methylimidazolium iodide (EMII), a typical ionic conductor, could be effectively inhibited from crystallization by TIPIL, which has been characterized by several testing. Thus, as a crystal growth inhibitor, TIPIL was used into EMII based solid-state dye-sensitized solar cells (ssDSSCs). Compared with the reference device, the DSSC containing TIPIL showed improved photovoltaic conversion efficiency up to 5.37%, and displayed excellent long-term stability. These results provide us a feasible method to explore new crystal growth inhibitors for ssDSSCs.

A compact layer (blocking layer) can effectively block the direct contact between the fluorine-doped tin oxide (FTO) glass substrate and electrolyte in dye-sensitized solar cells (DSSCs). The TiCl 4 hydrolysis has been widely adopted for preparing the TiO 2 compact layer (H-TiO 2 ). However, the TiCl 4 aqueous solution is unstable for its high reactivity. To improve the chemical stability of TiCl 4 aqueous solution, the Ti 4+ is encapsulated by the polymer, polyethyleneimine (PEI). Experimentals show that the Ti-PEI precursor solution can maintain their initial performances for several months. The resulting TiO 2 film (P-TiO 2 ) grown by the Ti-PEI precursor is dense, smooth and uniform without any visible and detectable cracks or voids. The P-TiO 2 compact layer is even denser than the H-TiO 2 compact layer, suggesting reducing the electron recombination and prolonging the electron lifetime in dye-sensitized solar cells. Indeed, the electron lifetime of the DSSC based on the P-TiO 2 is 13.15 ms, which is longer than the 10.83 ms based on H-TiO 2 . Meanwhile, the power conversion efficiency of the DSSC based on P-TiO 2 compact film is about 12.5% higher than that based on H-TiO 2 . Therefore, this encapsulation technology can not only improve the stability of the metal ions solution but also meet a large-scale fabrication demand of the TiO 2 compact layer in future DSSCs.

We report oxygen vacancies (OVs) rich hexagonal ReO3 nanostructured electrocatalysts for efficient hydrogen generation. Through a simple argon plasma exposure, OVs are introduced into the ReO3 nanoparticles (NP) and nanosheets to enhance electrocatalytic activities with decreasing overpotentails from 157 mV and 178 mV to 138 mV and 145 mV at the current density of 10 mA cm-2, respectively. As-processed OVs rich ReO3 NP exhibit a good stability during electrochemical measurements for 20 h in acidic electrolyte. The huge active surface area, abundant OVs and excellent conductivity contribute to the performance according to the experimental data. Further theoretical calculations show that the abundant OVs adsorb H with lower Gibbs free energy facilitating hydrogen evolution.

A direct comparison of charge transport and electronic traps in representative polymer–fullerene blend, poly (3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM), is carried out in dark and illuminated conditions based on the measurements of temperature-dependent current–voltage characteristics. In dark condition, the charge transport presents a transition from Ohmic to trap-limited current. While the trap-filled space charge limited current is observed under illumination at the same applied bias. From evaluations of trap density and energy distribution by a differential method, it is reveal that the diverse charge transport in dark and illuminated conditions is mainly caused by the different trap states distribution, which strongly affects the space charges and the electrical field in P3HT: PCBM blends.

Molybdenum trioxide (MoO 3 ) doped organic semiconductors have shown attractive applications in organic electric devices. The authors carried out an investigation on the origin of enhanced photoelectric characteristics in MoO 3 -doped pentacene films. Electrical properties including charge transport, trap density and conductivity in bulk MoO 3 -doped pentacene films were investigated through fundamental measurements of current-voltage characteristics. Electrical structure and conducting mechanism in MoO 3 -doped pentacene films were further evaluated by X-ray diffraction and X-ray photoelectron spectroscopy measurements. The experimental results suggest that the improved conductivity in MoO 3 -doped pentacene film was partly associated with the increased ratio of low Mo oxidation state (Mo 4+ ) with a fact of better conducting property of MoO 2 than that MoO 3 .

The underlayer plays an important role for organic–inorganic hybrid perovskite formation and charge transport in perovskite solar cells (PSCs). Here, we employ a classical organic small molecule, 5,6,11,12-tetraphenyltetracene (rubrene), as the underlayer of perovskite films to achieve 15.83% of power conversion efficiency with remarkable moisture tolerance exposed to the atmosphere. Experiments demonstrate rubrene hydrophobic underlayer not only drives the crystalline grain growth of high quality perovskite, but also contributes to the moisture tolerance of PSCs. Moreover, the matching energy level of the desirable underlayer is conductive to extracting holes and blocking electrons at anode in PSCs. This introduction of organic small molecule into PSCs provides alternative materials for interface optimization, as well as platform for flexible and wearable solar cells.

Roll-off phenomena in power efficiency for rubrene-based mixed single layer organic light emitting devices is investigated. The evaluation of operational temperature demonstrates that Joule heating is not the main reason for roll-off in power efficiency with current density. Co-doping method through rubrene co-doping with some additive dopant, C6, DCJTB and Nile red, in mixed single layer are proposed for suppressing the roll-off in power efficiency. By co-doping suitable Nile red with rubrene, the efficiency roll-off is found to be largely improved in whole range of current density. Moreover, improved device performance is also realized even if with a 3 wt% fluorescent doping concentration. The improved performance is ascribed that there exists a competitive emission mechanism with respect to different dopant.

Electroluminescence and photovoltaic properties were observed simultaneously in a small molecular rubrene-doped poly(3-hexylthiophene):1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 blends based organic solar cells (OSCs). With optimized rubrene doping ratio, the device showed photovoltaic (PV) property with a power convention efficiency 1.05% under illumination and electroluminescence (EL) characteristics with a maximum luminance 65 cd/m 2 at higher bias, respectively. It provides a new route to realize the PV and EL bi-functional organic devices. In addition, the EL imaging in OSCs is expected to provide valuable information in the film defect conditions for understanding the blends internal conditions, meliorating the film quality, and further improving the device performance.

We investigated the carrier injection properties in small molecular organic light emitting devices with a mixed single layer by measuring current–voltage characteristics using Au/MoO 3 as hole and Al alloy as electron injection electrodes. The carrier injection mechanism at the interface was primarily ascribed to the Schottky thermionic emission with the barrier height of 0.25 eV for holes and 0.67 eV for electrons. It was found that the barrier height of the electron was dependent on LUMO level of electron transport material. In addition, the interfacial state analysis demonstrated that the electron barrier height was also dependent on the interfacial conditions of the devices.

Inverted top-emission organic light emitting devices (TEOLEDs) with a mixed single layer by mixing of electron transport materials (PyPySPyPy and Alq 3 ), hole transport material (α-NPD) and dope material (rubrene) were investigated. Maximum power efficiency of 3.5 lm/W and maximum luminance of 7000 cd/m 2 were obtained by optimizing the mixing ratio of PyPySPyPy:Alq 3 :α-NPD:rubrene=25:50:25:1. Luminance and power efficiency of mixed single layer device were two times improved compared to bi-layer heterojunction device and tri-layer heterojunction device. Lifetime test also shows that the mixed single layer device exhibits longer operational lifetimes of 343 h, which is three times longer than the 109 h for tri-layer device, and two times longer than the 158 h for bi-layer device. In addition, the maximum luminance and power efficiency were obtained at 20,000 cd/m 2 and 7.5 lm/W, respectively, when a TPD layer of 45 nm was capped onto the top metal electrode.

The relative densities of SiCl n ( n =0–2) in SiCl 4 radio frequency (rf) glow discharge plasma are measured by mass spectrometry. The effects of discharge parameters, including rf power, discharge pressure, substrate temperature and SiCl 4 flow rate on the relative densities of SiCl n ( n =0–2) are investigated in detail. The experimental results demonstrate that the relative densities of SiCl n ( n =0–2) in SiCl 4 plasma are dependent strongly on these discharge parameters. An optimum configuration of discharge parameters (low rf power, high discharge pressure, low substrate temperature and low flow rate), which enhanced the formation of SiCl n ( n =0–2) radicals, was searched. Further, researching of SiCl n ( n =0–2) spatial distribution for seeking a suitable deposition condition is beneficial for understanding the deposition mechanism of thin films.

A new method, straight-line fitting, is proposed for measuring neutral radicals in plasma by a residual gas analyzer. Compared to threshold-ionization mass spectrometer, the proposed method is suited to all mass spectrometers, even if the minimum electron energy of the mass spectrometer is larger than the ionization threshold of the radicals. Moreover, the effects of the formation of daughter ions in the mass spectrometry ionization chamber are discussed. The results show that the effects of neutral radicals being ionized into fragment ions can be neglected during the course of deducing plasma depletion fraction within the deviation of the statistical fluctuation. In order to estimate the feasibility and reliability of this method, SiH n ( n = 0–3) radicals in an SiH 4 plasma and SiCl n ( n = 0–2) radicals in an SiCl 4 plasma are measured. The experimental results demonstrate that this newly proposed method is universal and more accurate than the previous one.

Growth of nano-crystalline silicon (nano-Si) films from hydrogen-diluted SiCl4 by the plasma enhanced chemical vapour deposition technique at 250 °C has been studied through mass spectrometry, Langmuir probe diagnostic techniques and Raman spectra measurements. The effects of the hydrogen dilution ratio on the relative densities of SiCln (n = 0–2) in SiCl4/H2 plasma are investigated. The average electron energy (Ee) and electron density (Ne) in SiCl4/H2 plasma increase with the hydrogen dilution ratio till their maxima at 9.25 eV and 3.7 × 109 cm−3, respectively. A suitable hydrogen dilution ratio R (0.4–0.67) is beneficial for the formation of SiCln (n = 0–2) radicals because Ee and Ne both have maxima in this range. More SiCln (n = 0–2) radicals will improve the deposition rate and film quality. In addition, hydrogen radicals play an important role in the surface reaction process. The reaction of H and SiCln (n = 0–2) on the growing surface is beneficial for creating dangling bond sites and prompting the film growth, and the exothermic reaction exothermic energy of H with Cl on the film-growing surface results in the increase of the effective temperature of the film growth.

The authors investigate the influence of two hole interfacial materials poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) and aqueous solution-processed MoO3 (sMoO3) on cell stability. sMoO3-based device demonstrated obviously improved stability compared to PEDOT:PSS-based one. Current-voltage characteristics analysis is carried out to investigate the effect of the hole interfacial layers on the cell stability. The formation of additional trap states at the interfaces between the hole interfacial layer and the active layer in degraded devices is verified by a differential method. Improved cell stability is attributed to a relatively stable sMoO3 interfacial layer compared to PEDOT:PSS by comparing their different trap states distributions.

The authors demonstrate a pentacene/C60 heterojunction organic solar cell utilizing MoO3-doped pentacene thin films as an interfacial layer at anode and a multicharge-separation layer between pentacene and C60, respectively. The short-circuit current density and the open-circuit voltage were improved simultaneously compared with the reference device, resulting in an improvement in power conversion efficiency from 0.97% to 2.29%. Absorption spectra measurement, surface morphology analysis, and interfacial evaluation at anode side in the hole-dominant devices were carried out to reveal the functions of MoO3-doped pentacene films in OSCs.

Measurements of the current density–voltage (J–V) characteristics of a poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM)-based electron-dominated device as functions of temperature were carried out. A transport transition from three-dimensional variable range hopping (VRH) to space-charge-limited current (SCLC) with an exponential distribution of traps (filled and unfilled) was observed. The bulk trap density, about 1018 cm-3, of the P3HT:PCBM blend film was evaluated by the differential method. A shift to the lowest unoccupied molecular orbital (LUMO) state of PCBM for trap density distribution was observed owing to the temperature dependence of the Fermi level of PCBM materials. It is supposed that the Fermi level of PCBM materials is strongly temperature-dependent similarly to that of amorphous silicon semiconductors.

We report on the enhanced carrier injection in pentacene thin-film transistors with a thin MoO3-doped pentacene layer between pentacene semiconductor and the source-drain electrodes. Device performance including drain current, field effect mobility, and threshed voltage are improved by employing a MoO3-doped pentacene thin layer. The barrier height at the Au/pentacene interface is lowered from 0.12 to 0.05 eV after inserting a MoO3-doped pentacene thin layer between them. The reduced barrier height is attributed to the formation of a good contact between MoO3-doped pentacene and Au owing to smoothed surface morphology of pentancene and suitable band bending by MoO3 doping.

The authors investigate the effects of a small molecular dye, perylene, on the performance of organic solar cells based on poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) blends. The short-circuit current density is improved, and a maximum 27% enhancement in power conversion efficiency is achieved by doping suitable perylene into P3HT:PCBM blends. It is attributed to be the enhanced absorption of perylene doped P3HT:PCBM blends, which is also confirmed in single-carrier devices. Moreover, the barrier height at the anode/blend is largely lowered from 0.61 eV to 0.28 eV through evaluating temperature dependence of current-voltage characteristics.

The authors investigate efficiency roll-off in 5,6,11,12-tetraphenylnaphthacene (rubrene)-based mixed single layer top-emission organic light emitting devices by codoping with special additive dopants. The efficiency roll-off is suppressed after codoping rubrene with phenoxazone (Nile red). Due to dual nature of rubrene acting as electron hopping site and hole trap, it not only captures carrier producing light but also transfers energy to Nile red and then produces light. Meanwhile, Nile red molecules can also get energy from host directly. There exists a competitive process between three emission mechanisms, which depress self-quenching of dye molecules during emission, resulting in improved efficiency and lowered driving voltage.

Due to the good photocatalytic activity, the TiO2@CNTs thin film is highly desirable to apply to the self-cleaning glass for green intelligent building. Here, the TiO2@CNTs thin film has been successfully achieved by polymer-assisted approach of an aqueous chemical solution method. The polymer, polyethylenimine, aims to combine the Ti4+ with CNTs for film formation of TiO2@CNTs. The resultant thin film was uniform, highly transparent, and super-hydrophilic. Owing to fast electron transport and effectively hindering electron-hole recombination, the TiO2@CNTs thin film has nearly twofold photocatalytic performance than pure TiO2. The TiO2@CNTs thin films show a good application for self-cleaning glasses. Electronic supplementary material The online version of this article (doi:10.1186/s11671-016-1674-4) contains supplementary material, which is available to authorized users.