Formation Of High-quality Films Research Articles

Structural, optical and electrical properties of sulphide based heterojunction thin film

This contribution presents structural, optical and electrical properties of PbS/CdS thin films at different annealing temperatures. The XRD analysis reveal the existence of three different crystalline phases, i.e., the beta-CdS, hawleyite-CdS and greenockite-alpha-CdS phases within the CdS-shell of PbS/CdS core shell thin film. The dislocation density and microstrain decreased with annealing temperatures indicating a decrease in lattice imperfections and formation of high quality film and it can be attributed to the increase in grain size of the film with increase in annealing temperatures. Optical studies placed the band gaps at 1.25eV-1.75eV. About the same magnitude were found from electrical conductivity test. The samples exhibited high conductivity with increasing annealing temperatures which resulted to the bumping of electrons from the valence band to the conduction band. The high absorbance suggest that the film could be coated on collectors to enhance solar energy collection. The achieved band gaps placed the PbS/CdS fabricated with the presented method as a good material for solar photovoltaic applications.

Preparation of TiO[formula omitted] electron transport layer by magnetron sputtering and its effect on the properties of perovskite solar cells

Magnetron sputtering technology benefits from an easy process parameter adjustment strategy, good experimental reproducibility, and high-quality film formation; thus, it is widely used in thin-film electronic devices. In the present work, the thickness and morphology of the TiO2 electron transport layer were controlled by magnetron sputtering time, and based on this technology, planar heterojunction perovskite solar cells were prepared. The results showed that with an increase in the sputtering time, the surface roughness of the TiO2 film decreased, and the electrical homogeneity and square resistance of the film increased. Especially, the film transmittance showed a maximum value of 82.29% at 45 min of deposition, and the so prepared perovskite solar cells exhibited the highest photoelectric conversion efficiency of up to 12.42%.

Triptycene-imbedded thermally activated delayed fluorescence emitters with excellent film morphologies for applications in efficient nondoped and doped organic light-emitting devices

Thermally activated delayed fluorescence (TADF) materials with high luminescence efficiencies, short lifetimes, excellent thermal stability and high-quality film formation are highly desired to realize efficient organic light emitting diodes (OLEDs) with low efficiency roll-off. Herein, two asymmetric TADF molecules consisting of triptycene-fused benzophenone serving as an electron acceptor, and dimethylacridin and phenoxazine as electron donors are reported. The comparative study reveals that the introduction of triptycene scaffold strengthens the molecular rigidity and the intermolecular interactions in aggregated states, which endow the titled materials with significantly improved thermal stability, film formation quality and mechanofluorochromism behaviors. The triptycene-imbedded compound TCO-DMAC emits fast efficient delay fluorescence with photoluminescence quantum yield (PLQY) of 0.92 and short lifetime of 4.94 μs in doped evaporated film, based on which the bluish-green doped OLED achieved an external quantum efficiency (EQE) of 21.2%, a current efficiency (CE) of 57.3 cd/A, a power efficiency (PE) of 62.3 lm/W, and a maximum brightness of 15780 cd/m2. It is worth mentioning that the evaporated neat film of TCO-DMAC exhibit high PLQY of 0.69 and short delay fluorescence lifetime of 4.37 μs. The non-doped OLED achieved an external quantum efficiency (EQE) of 15.6%, a turn-on voltage of 2.8 V and a maximum brightness of 13830 cd/m2 with only minor efficiency roll-off of 3.8% at a high luminance of 1000 cd/m2.

Impact of Hydroxyl Groups Boosting Heterogeneous Nucleation on Perovskite Grains and Photovoltaic Performances

Surface energy is a key factor in controlling the kinetics of nucleation and growth of perovskite, which are crucial for the formation of high quality films and the photovoltaic efficiency of solar...

Precursor synthesis strategy for polycyclic aromatic conjugated polymers on the application of supercapacitors

Polycyclic aromatics (PCAs) possess excellent photoelectric properties, but the construction of such compounds has been a quite challenging subject of study, mainly due to very low solubility. Herein we report a precursor synthesis strategy for polycyclic aromatic conjugated polymers. A soluble precursor polymer, that containing fusible “double U-shaped aromatic” (DUA) and perylenetetracarboxydiimide (PDI) units, was firstly synthesized by Suzuki coupling. The stereo aromatic units in polymer backbone were found to be converted into polycyclic aromatic units, i.e. hexa-peri-hexabenzocoronene (HBC), by chemical or electrochemical oxidation, which resulted in a formation of insoluble polycyclic aromatic conjugated polymers. The electrochemical oxidations that occurred at the interface of electrode and solution exhibited higher cyclization reactivity and leads to the formation of high quality films on the electrode surface. Characterization by Raman and UV-visible (UV-Vis) spectroscopy validated the successful formation of this HBC structure. Some potential applications of such thin films are being explored, and here we focus on the characteristics of supercapacitors based on their excellent electrochemical properties.

Structural characterization of niobium oxide thin films grown on SrTiO3 (111) and (La,Sr)(Al,Ta)O3 (111) substrates

Niobium oxide thin films have been grown by molecular beam epitaxy on SrTiO3 (STO) (111) and (La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT) (111) substrates. Transmission electron microscopy (TEM) confirmed the formation of high quality films with coherent interfaces. Films grown with higher oxygen pressure on STO (111) resulted in a (110)-oriented NbO2 phase with a distorted rutile structure, which can be described as body-centered tetragonal. The a lattice parameter of NbO2 was determined to be ∼13.8 Å in good agreement with neutron diffraction results published in the literature. Films grown on LSAT (111) at lower oxygen pressure produced the NbO phase with a defective rock salt cubic structure. The NbO lattice parameter was determined to be a ≈ 4.26 Å. The film phase/structure identification from TEM was in good agreement with in situ x-ray photoelectron spectroscopy measurements that confirmed the dioxide and monoxide phases, respectively. The atomic structure of the NbO2/STO and NbO/LSAT interfaces was determined based on comparisons between high-resolution electron micrographs and image simulations.

Low Temperature Growth of Cu2ZnSnS4 Thin Films By Solution-Based Mist Chemical Vapor Deposition Method

Introduction The Cu-III-VI2 chalcopyrite semiconductors such as Cu(In,Ga)(S,Se)2 (CIGSSe) have been proved to be successful candidate for photovoltaic applications. CIGSSe thin film solar cells show high power conversion efficiencies over 20 % and these results promoted to explore other related semiconductors. Cu2ZnSnS4 (CZTS) is one of the promising semiconductor for absorber layer in thin film solar cells. The elements zinc (Zn) and tin (Sn) in CZTS are nontoxic and relatively abundant compared to indium (In) and gallium (Ga) in CIGSSe. CZTS thin films have a direct band gap of about 1.5 eV, which is ideal for solar cells, p-type conductivity, and high absorption coefficient (> 104 cm-1). Various methods have been applied for CZTS thin film fabrication, including sputtering, evaporation, sulfurization of precursors, spray pyrolysis and chemical techniques. However these techniques have several problems such as high energy consumption, not suitable for large-area fabrication, and require high temperature anneal and/or sulfurization processes. To overcome the above problems, we applied a mist chemical vapor deposition (CVD) technique to fabricate CZTS thin films. This technique allows high quality film formation in atmospheric pressure without vacuum equipment and is able to be easily expanded for large area substrates. In addition, the mist CVD have already realized the thin film formations of transparent conductive oxides (TCOs) which constitute CZTS-based solar cells. A wide variety of precursor materials have been considered to be grown at lower growth temperatures using mist CVD method. In this presentation, we will show growth of CZTS thin films with this technique. Experimental We used fine channel type mist CVD for the present purpose. The reaction region is composed of a fine channel structure above the substrate, in which the precursor materials are effectively reacted. A solution containing precursor materials was ultrasonically atomized and the mist particles formed were supplied onto a substrate, using nitrogen carrier gas. Thin films are obtained by the thermal decomposition of precursor materials on the substrates. CZTS thin films were fabricated onto glass substrates. The precursor materials used for CZTS thin film fabrication were metal chloride, metal acetylacetonate, and/or metal acetate as Cu, Zn and Sn sources and thiourea as S source. These precursor materials were diluted in methanol with the stoichiometric concentration ratio. The growth temperatures were set below 450 oC. The structure of the CZTS thin films has been analyzed by X-ray diffraction (XRD). The concentration and optical properties of the samples were characterized by energy dispersive X-ray analysis (EDX) and UV-visible spectrometry, respectively. Van-der-Pauw-Hall measurements were carried out at room temperature in order to characterize the electrical properties. Results and discussion CZTS thin films grown from a source solution which contains metal chloride (CuCl2, ZnCl2 and/or SnCl2) have various compositions far from stoichiometric ratio and observed not only diffraction peaks of CZTS but also different phase peaks indexed to Cu2-xS or ZnS. The thin films whose sources were chloride-related ones consisted CZTS + Cu2-xS or CZTS + ZnS, which depend on the growth temperatures. In contrast, CZTS thin films grown from a source solution which contains only acetylacetonate-related sources, no diffraction peaks indexed to different phase were observed and film compositions were almost stoichiometric ratio. These results indicate that chloride sources realize lower activation energy of Cu2-xS or ZnS, Therefore, Cu2-xS or ZnS were grown even lower growth temperatures at the same time as growing CZTS. On the other hand, acetylacetonate-related sources have higher activation energy of different phase and inhibit the growth of Cu2-xS and ZnS. Conclusion CZTS thin films were fabricated by a non-vacuum mist CVD technique. CZTS was grown in the low temperature region below 350 oC. Because of the low-cost source materials and simple production process used, the fabricated films may load to photovoltaic applications.

Effect of Hydrogen on Silicon Nitrides Formation by Microwave Excited Plasma Enhanced Chemical Vapor Deposition

The gas composition is one of the most important parameters for reducing process temperature of the plasma enhanced chemical vapor deposition. We investigate the effect of the gas flow rate of SiH4, H2, and N2 on the quality and the deposition rate of the silicon nitride films (SiNx) formed by the microwave excited PECVD. The SiH4 flow rate is most important parameter for controlling the deposition rate and the film quality in the PECVD using N2, H2, SiH4 gasses. The deposition rate strongly depends on the SiH4 flow rate; however the film quality was degraded with the increase of the flow rate. The hydrogen has an optimum flow rate for the high deposition rate and high quality film formation. The hydrogen effectively dissociates the SiH4 gas and makes the nitridation species (NHx), as the result, the optimal hydrogen improves the reaction efficiency of SiH4 and NHx.

Fabrication of high-quality amorphous silicon film from cyclopentasilane by vapor deposition between two parallel substrates.

Cyclopentasilane converts into amorphous silicon film between two parallel substrates under atmospheric pressure by thermal decomposition at 350-400 °C, which combines the advantages of high throughput with cost reduction and high quality film formation.

VO2(110) film formation on TiO2(110) through post-reduction of ALD grown vanadium oxide

Abstract Epitaxial VO 2 film was produced through post-reduction of vanadium oxide film grown on rutile TiO 2 (1 1 0) by atomic layer deposition (ALD) method. The ALD grown film was transformed to VO 2 after annealing at 350 °C under 2% hydrogen gas flow. Metal–insulator phase transition of the transformed VO 2 (1 1 0) film has been characterized with resonance photoemission and soft X-ray absorption spectroscopy. Formation of high quality film is evident from clear metal–insulator transition features in oxygen K-edge absorption spectra and metallic peaks in the Fermi level in V 2p-3d resonance photoemission map taken at 127 °C. The VO 2 film formation through the post-reduction of ALD grown vanadium oxide at considerably low temperature could provide route to incorporate VO 2 conformal layer into an integrated device utilizing the metal–insulator transition.

Improvement in the crystallinity of ZnO thin films by introduction of a buffer layer

The influence of pre-deposition of homo-buffer layers on film quality is studied as functions of temperature and duration of pre-deposition, for zinc oxide (ZnO) crystalline films prepared by pulsed laser deposition on sapphire (0 0 0 1) substrates. This preparation technique is necessary to prepare high quality films suitable for the development of ZnO devices. Crystallinity and surface morphology were characterized by X-ray diffraction (XRD), reflection high energy electron diffraction and scanning electron microscopy. The line width of the rocking curve observed for ZnO (0 0 0 2) XRD of ZnO films decreases (to 0.09° from 0.2–0.3°) upon introduction of a buffer layer of ZnO itself at a low temperature approximately 500 °C, indicating the formation of high quality films. The surface morphology and flatness were also improved. The film prepared under optimal conditions shows a high optical transmittance of ∼90% with a steep falloff at 380 nm and a fairly small carrier concentration (1.8×10 17 cm −3). These results imply that the buffer layer relaxes the strain due to lattice mismatch between ZnO and sapphire (by 18%) and improves the film crystallinity.

Nickel β-diketonate complexes as precursors for the photochemical deposition of nickel oxide thin films

In this paper we report the utilization of amorphous films of Ni(II) diketonate complexes as precursors for the direct photochemical deposition of thin films of nickel oxides. The UV photolysis of amorphous thin solid films of Ni(PhCOCHCOPr)2 results in the loss of all ligands from the coordination sphere. The acetylacetone derivative was chosen for the solid state photochemistry because the presence of the long carbon chains or highly branched hydrocarbons substituents, lowers the intermolecular interactions and allows the formation of high quality films upon spin-coating. The surface morphology of the films was observed by scanning electron microscopy and showed excellent quality without islands or other imperfections. The formation of NiO was determined by X-ray difraction and Auger spectroscopy analysis. The photochemical deposition of patterns of NiO was shown to be compatible with standard lithographic techniques by the lithography of 100 × 2 μm lines.

Solid-state photochemistry of a Cu(II) β-diketonate complex: the photochemical formation of high quality films of copper(II) oxide

In this communication, we report the utilization of amorphous films of metal-organic molecules for the direct photochemical deposition of thin films of copper(II) oxide. This is effected by UV photolysis of amorphous thin solid films of Cu[CH 3(CH 2) 8COCHCOC 4H 9] 2, which results in the loss of all ligands from the coordination sphere. The acetylacetone derivative was chosen for the solid-state photochemistry because the presence of the long carbon chains or highly branched hydrocarbons substituents lowers the intermolecular interactions and allows the formation of high quality films upon spin-coating. The surface morphology of the films was observed by optical microscopy and showed excellent quality with no visible grains, islands, or other imperfections. The compositions of the films were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Auger spectroscopy. The copper(II) oxide films are free from carbon contamination in the bulk as shown by Auger electron spectroscopy.

Low-temperature large-grain poly-Si direct deposition by microwave plasma enhanced chemical vapor deposition using SiH4/Xe

Polycrystalline silicon is grown at a temperature of 300 °C by microwave-excited plasma enhanced chemical vapor deposition using SiH4/Xe. The grain size measured by x-ray diffraction is about 25 nm. High-density (>1012 cm−3) plasma having very low electron temperature (<1 eV) is excited by microwave irradiation using radial line slot antenna. We present the implementation of this system for the growth of poly-Si. Low-energy (3 eV), high-flux ion bombardment utilizing xenon ion on a growing film surface activates the film surface and successfully enhances surface reaction/migration of silicon, resulting in high quality film formation at low temperatures.