Low-temperature Solution Method Research Articles

High performance planar perovskite solar cells based on CH3NH3PbI3-x(SCN)x perovskite film and SnO2 electron transport layer prepared in ambient air with 70% humility

In this work, the efficient and stable planar perovskite solar cells (PSCs) based on CH3NH3PbI3-x(SCN)x perovskite layer and low-temperature processed SnO2 electron transport layer (ETL) have been fabricated in ambient air with 70% humility. The maximum processing temperature of the PSCs is only 150 °C. The effect of SnO2 solution concentrations on photoelectronic characteristics of the PSCs has been symmetrically investigated. At the optimized SnO2 concentration, the PSCs based on SnO2 ETL (SnO2-PSCs) achieve the champion power conversion efficiency (PCE) of 16.23% and average PCE of 15.82%, being much higher than that of the reference PSCs based on TiO2 ETL. The higher PCE of SnO2-PSCs can be attributed to the improved carrier transfer and collection, and the suppressed charge recombination. Importantly, the SnO2-PSCs without encapsulation demonstrate an excellent long-term stability. After being stored in ambient air with 70% humidity for 30 days, the PCE of the unsealed SnO2-PSCs decay only 15%. This work presents a simple low-temperature solution method to fabricate efficient and stable PSCs in ambient air with high humidity, which is beneficial for future application of PSCs.

Centimeter-Sized Inorganic Lead Halide Perovskite CsPbBr3 Crystals Grown by an Improved Solution Method

As a member of the lead-halide perovskite family, inorganic perovskite CsPbBr3 exhibits excellent optical and electrical properties with higher stability to the environment. However, former efforts to obtain large-size CsPbBr3 single crystals with satisfactory quality using low temperature solution methods reached limited results. In this work, we have studied the growth of CsPbBr3 crystals using the antisolvent vapor-assisted crystallization (AVC) method. By adjusting the mole ratio of PbBr2 and CsBr, the phase diagram of the final products is acquired. Five regions are identified, including the Cs4PbBr6 single phase region, Cs4PbBr6 and CsPbBr3 two phases region, CsPbBr3 single phase region, CsPbBr3 and PbBr2·2[(CH3)2SO] metastable two phases region, and CsPbBr3 and PbBr2·2[(CH3)2SO] two phases region. Three methods are adopted to improve the size and crystalline quality of CsPbBr3. The growth rate is effectively tailored by diluting the antisolvent MeOH solution using DMSO to reduce the MeOH vapor pres...

Speedy photocatalytic degradation of bromophenol dye over ZnO nanoflowers

A simple, low temperature solution method was employed to synthesize ZnO nanoflowers (NFs) using zinc nitrate as precursor for the photocatalytic degradation of bromophenol (Bph) dye. The synthesized materials exhibited well-defined flower like morphology comprised of several defined nanorods. The crystalline and optical observations manifested the high crystallinity of ZnO-NFs with wide band gap of ∼3.21eV. The synthesized ZnO NFs as catalysts presented a rapid degradation of Bph-dye with the degradation rate of ∼96% within 120min under the UV light irradiation. The fragmentations of Bph-dye after the photocatalytic reaction over ZnO-NFs were analyzed by interpreting the mass spectroscopy of degraded Bph-dye.

Electrochemical performance of 3D porous Ni-Co oxide with electrochemically exfoliated graphene for asymmetric supercapacitor applications

Ni-Co oxide, one of the binary metal oxides, has many advantages for use in high-performance supercapacitor electrode materials due to its relatively high electronic conductivity and improved electrochemical performance. In this work, Ni-Co oxide/electrochemically exfoliated graphene nanocomposites (NC-EEG) are successfully synthesized using a simple low temperature solution method combined with a thermal annealing treatment. Graphene sheets are directly obtained by an electrochemical exfoliation process with graphite foil, which is very simple, environmentally friendly, and has a relatively short reaction time. This electrochemically exfoliated graphene (EEG) can improve the electrical conductivity of the Ni-Co oxide nanostructures. The as-prepared NC-EEG nanocomposites have 3D porous architectures that can provide large surface areas and shorten electron diffusion pathways. Electrochemical properties were performed by cyclic voltammetry and galvanostatic charge/discharge in a 6M KOH electrolyte. The NC-EEG nanocomposites exhibited a high capacity value of 649Cg−1 at a current density of 1.0Ag−1. The asymmetric supercapacitors, manufactured on the basis of NC-EEG nanocomposites as a positive electrode and activated carbon (AC) as a negative electrode, exhibited a maximum energy density of 86Whkg−1 and a maximum power density of 16.5kWkg−1. It is believed that our 3D nano-architectured composites with excellent electrochemical performances would be promising candidates for supercapacitor materials.

Ag nanowire/ZnO nanobush hybrid structures for improved photocatalytic activity

Reverse-engineered Ag nanowire/ZnO nanobush hybrid structures have been synthesized for the first time by a combination of polyol method and low-temperature solution method. Through the elaborate control of Ag-to-ZnO weight ratio, vertically aligned ZnO nanobushes grew on the surface of well-faceted Ag nanowires. The Ag/ZnO hybrid nanostructures showed the crystal features of both Ag nanowires and wurtzite ZnO nanostructures. They exhibited strong UV absorption, whereas their photoluminescence spectra were much weaker than pure ZnO nanostructures due to the inhibited carrier recombination. The photocatalytic activity of Ag/ZnO hybrid nanostructures was greatly improved compared to pure ZnO nanostructures. Furthermore, they showed good cyclic performance and easy recovery from the test solution, demonstrating the possibility of their practical use.

Enhancement of external quantum efficiency and quality of heterojunction white LEDs by varying the size of ZnO nanorods

The size of ZnO nanorods (NRs) plays an important role in tuning the external quantum efficiency (EQE) and quality of light generated by white light emitting diodes (LEDs). In this work, we report on the enhancement of EQE and the quality of ZnO NR-based hetrojunction white LEDs fabricated on a p-GaN substrate using a low temperature solution method. Cathodoluminescence spectra demonstrate that ultraviolet (UV) emission decreases and visible deep band emission increases with an increase in the length of the ZnO NRs. The UV emission could be internally reabsorbed by the ZnO NR excitation, thus enhancing the emission intensity of the visible deep band. Photocurrent measurements validated the fact that the EQE depends on the size of ZnO NRs, increasing by 87% with an increase in the length of the ZnO NRs. Furthermore, the quality of white light was measured and clearly indicated an increase in the color rendering indices of the LEDs with an increase in the length of the ZnO NRs, confirming that the quality of light generated by LEDs can be tuned by varying the length of the ZnO NRs. These results suggest that the EQE and visible deep band emission from n-ZnONRs/p-GaN heterojunction LEDs can be effectively controlled by adjusting the length of the ZnO NRs, which can be useful for realizing tunable white LEDs.

Effect of CH 3 NH 3 I concentration on the physical properties of solution-processed organometal halide perovskite CH 3 NH 3 PbI 3

Abstract Organic-inorganic halide perovskite CH 3 NH 3 PbI 3 films were synthesized by low-temperature solution method by using a two-step spin-coating technique. We detailedly investigated the effect of the concentration of CH 3 NH 3 I solution on the morphology and optical properties of CH 3 NH 3 PbI 3 films, and a regular morphology evolution was observed. Further, temperature-dependent photoluminescence measurement was performed, and a structural phase transition of the CH 3 NH 3 PbI 3 films at 150 K was revealed by examining the temperature dependence of the peak positions and widths. In addition, the corresponding exciton binding energy and optical phonon energy of the CH 3 NH 3 PbI 3 films were extracted in the high-temperature tetragonal phase based on the experimental data. It can be anticipated that our results obtained provide valuable information for the understanding on the optical properties of perovskite CH 3 NH 3 PbI 3 , and also their future applications in optoelectronic devices.

Unique optical properties of Eu3 + doped l-histidine hydrochloride mono hydrate single crystals from low temperature growth technique

A low-temperature solution method was utilized to grow single crystals of Eu3+doped l-histidine hydrochloride monohydrate. The quality of the crystals was confirmed by high-resolution X-ray diffraction measurements with full width at half maximum (FWHM) of rocking curve at 8arc per sec. The incorporation of Eu3+ ions into the lattice was confirmed by functional group analysis using Fourier Transform Infrared (FTIR) spectroscopy. The amount of Eu3+ ions was found to be 0.08 weight (%) using energy dispersive X-ray analysis. The crystal's thermal and mechanical properties were tested as well. The unique spectral properties such as UV–Vis transmittance, nonlinear optical efficiency (NLO), photoluminescence (PL) and its lifetime were measured. The PL study revealed that the intensity of 5D0→7F2 emission of Eu3+ is stronger than that of 5D0→7F1 emission and the decay measurement showed a life time of 7.2410μs. The photoluminescence results prove that l-histidine hydrochloride monohydrate is a new, highly efficient host material for europium ion red emissions.

Facile one-pot synthesis of self-assembled quantum-rod TiO2 spheres with enhanced charge transport properties for dye-sensitized solar cells and solar water-splitting

We report a facile one-pot synthesis of self-assembled quantum-rod (sub-10 nm) TiO2 spheres (SQR-TiO2) via a low-temperature solution method and demonstrate the impact of SQR-TiO2 on the charge transport/collection properties of photoelectrochemical devices. The effects of dissolved ions (e.g. Na+ and Cl−) on the particle morphology was investigated through comparative experiments using various additives including Na2SO4, Na-oleate, Na2HPO4, NH4Cl, (NH4)2SO4, and N2H4. Importantly, we found that Na+ ions play a crucial role in the self-assembly process, while Cl− ions induce the nanorod morphology. With the synthesized SQR-TiO2 (∼400 nm in size), dye-sensitized solar cells and photoelectrochemical water-splitting devices were produced. The results show that the SQR-TiO2 improves light capturing and charge transport properties for both devices compared to other types of TiO2 (nanoparticles and nanoparticle-assembled spheres), and this is attributed to its unique morphology features.

A new low-temperature solution route to Aurivillius-type layered oxyfluoride perovskites Bi2MO5F (M = Nb, Ta) as photocatalysts

Aurivillius oxyfluoride perovskites exhibit great potential in photocatalysis, which are generally prepared by high-temperature solid-state reactions and some impurity phases are always unavoidable. Herein, a new low-temperature solution method has been successfully developed for the synthesis of Bi2NbO5F and Bi2TaO5F pure phases. The electron microscopy results reveal that the products were composed of the hierarchical hollow spheres with porous surface. The formation and growth mechanisms of the products were proposed based on the time-dependent evolution. The experimental band gaps of Bi2NbO5F (2.86eV) and Bi2TaO5F (2.95eV) were also first obtained. The photodegradation tests demonstrated that the products could be effectively served as catalysts for degradation of Rhodamine B and methyl orange under UV-light irradiation via the photocatalytic reaction, and also could be used in visible-light degradation of Rhodamine B via the photosensitization process. This low-temperature solution preparation of Aurivillius oxyfluorides opens a new facile route to tackle the versatile chemistry of various oxyfluoride perovskites.

Low-Temperature Grown ZnO Nanoflakes for Dye Sensitized Solar Cell Application

Herein, we report the simple and facile synthesis of well-crystalline ZnO nanoflakes and their use as an anode material to fabricate dye-sensitized solar cell ( DSSC). The nanoflakes were synthesized by simple low-temperature solution method and characterized by several techniques to examine the morphological, structural, optical and compositional properties. The structural characterizations confirmed that the synthesized nanoflakes are well-crystalline and possessing wurtzite hexagonal phase of ZnO. The morphological investigation revealed that the synthesized material possess flakes shaped morphologies which are grown in high-density. The compositional properties of nanoflakes confirmed the pure phase of ZnO. UV-Vis spectroscopy was used to determine the optical properties of as-synthesized ZnO nanoflakes. The as-synthesized ZnO nanoflakes were used as anode materials for the fabrication of dye-sensitized solar cell ( DSSC) which exhibited an overall light-to-electricity conversion efficiency of similar to 1.32%, open-circuit voltage (VOC) of 0.702 V, short-circuit current (J(SC)) of similar to 2.97 mA/cm(2) and fill factor (FF) of 0.63.

ZnO hollow nano-baskets for mineralization of cationic dye

The hollow nano-baskets (HNBs) of zinc oxide (ZnO) were synthesized by a simple low temperature solution method and used for the degradation of rhodamine 6G (Rh6G) dye. Well-defined hollow nano-baskets morphology of ZnO was observed which displayed a band gap of ~3.26eV. The photocatalytic degradation results revealed that the synthesized ZnO-HNBs exhibited a rapid degradation rate of ~97% of Rh6G-dye within ~90min. The mineralization of Rh6G-dye was examined before and after the photocatalytic reaction by a mass spectroscopy of the dye. The rapid and high degradation of Rh6G-dye might be attributed to ZnO hollow nanostructures via improved catalyst contact with dye by the inner and external surface of ZnO.

Hydrothermal Synthesis of ZnO Structures Formed by High-Aspect-Ratio Nanowires for Acetone Detection.

Snowflake-like ZnO structures originating from self-assembled nanowires were prepared by a low-temperature aqueous solution method. The as-grown hierarchical ZnO structures were investigated by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The results showed that the snowflake-like ZnO structures were composed of high-aspect-ratio nanowires. Furthermore, gas-sensing properties to various testing gases of 10 and 50 ppm were measured, which confirms that the ZnO structures were of good selectivity and response to acetone and could serve for acetone sensor to detect low-concentration acetone.

Synthesis of wheatear-like ZnO nanoarrays decorated with Ag nanoparticles and its improved SERS performance through hydrogenation

Semiconductor/noble metal composite SERS substrates have been extensively studied due to their unique bifunctionality. In this work, wheatear-like ZnO nanoarrarys have been fabricated via a modified low-temperature solution method. The hierarchical nanostructures that are constructed by stacked nanoflakes and long whiskers of ZnO possess a substantial number of characteristic nano corners and edges, which are proved to be beneficial to deposit more Ag nanoparticles (NPs). Furthermore, hydrogenated wheatear-like ZnO/AgNP composite substrates are achieved via a safe and facile solid hydrogen source (NaBH4). The hydrogenated ZnO/AgNPs (H-ZnO/Ag) substrates exhibit greatly improved SERS activity in detecting R6G molecules with an enhancement factor (EF) up to ∼0.49 × 108, over two orders of magnitude higher than that of the substrates before hydrogenation. The outstanding SERS performance of wheatear-like H-ZnO/Ag substrates benefits from the emerging porous structure of ZnO and abundant surface defects introduced by hydrogenation. In addition, the as-prepared substrates also show high detection sensitivity, good repeatability and recyclability, indicating great potential for practical applications.

Dynamic Growth of Pinhole-Free Conformal CH3NH3PbI3 Film for Perovskite Solar Cells.

Two-step dipping is one of the popular low temperature solution methods to prepare organic-inorganic halide perovskite (CH3NH3PbI3) films for solar cells. However, pinholes in perovskite films fabricated by the static growth method (SGM) result in low power conversion efficiency (PCE) in the resulting solar cells. In this work, the static dipping process is changed into a dynamic dipping process by controlled stirring PbI2 substrates in CH3NH3I isopropanol solution. The dynamic growth method (DGM) produces more nuclei and decreases the pinholes during the nucleation and growth of perovskite crystals. The compact perovskite films with free pinholes are obtained by DGM, which present that the big perovskite particles with a size of 350 nm are surrounded by small perovskite particles with a size of 50 nm. The surface coverage of the perovskite film is up to nearly 100%. Such high quality perovskite film not only eliminated pinholes, resulting in reduced charge recombination of the solar cells, but also improves the light harvesting efficiency. As a result, the PCE of the perovskite solar cells is increased from 11% for SGM to 13% for DGM.

Electrochemical Water Oxidation of Ultrathin Cobalt Oxide-Based Catalyst Supported onto Aligned ZnO Nanorods.

A stable and durable electrochemical water oxidation catalyst based on CoO functionalized ZnO nanorods (NRs) is introduced. ZnO NRs were grown on fluorine-doped tin oxide (FTO) by using a low-temperature chemical solution method and were functionalized with cobalt oxide by electrochemical deposition. The electrochemical water oxidation performance of cobalt oxide functionalized ZnO NRs was studied under alkaline (pH = 10) conditions. From these studies, it is noticed that cobalt oxide functionalized ZnO NRs show electrocatalytic activity toward water oxidation with current density on the order of several mA cm(-2). Further, 30 s CoO deposited ZnO nanorods exhibited excellent galvanostatic stability at a current density of 1 mA cm(-2) and potentiostatic stability at 1.25 V vs Ag/AgCl over an electrolysis period of 1 h.

Defect Levels in Nuclear Detector Grade Cd0.9Zn0.1Te Crystals

Nuclear detector grade semi-insulating Cd0.9Zn0.1Te (CZT) crystals were grown by a low temperature solution method from in-house zone refined precursor materials. The extended defects due to secondary phases of tellurium inclusions/precipitates in the grown crystals were characterized by a non-destructive electron beam induced current (EBIC) imaging method. The EBIC results were correlated with the infrared (IR) transmittance mapping, which clearly shows the variation of contrast is due to non-uniform distribution of tellurium inclusions/precipitates in CZT crystals. Electrical characteristics of defect levels in the fabricated detectors were further investigated by thermally stimulated current (TSC) measurements. Pulse height spectra (PHS) measurements were carried out using nuclear radiation sources of 241Am (59.6 keV) and 137Cs (662 keV) and energy resolutions of 6.2% and 1.6% respectively were achieved.

Investigations on the Low Temperature Solution growth, etching, laser damage threshold, Photoluminescence, electrical characterization and nonlinear optical properties of organic material: Ammonium hydrogen l-malate

Optically good quality bulk organic nonlinear optical crystal ammonium hydrogen l-malate (AHM) of crystal size 25mm×26mm×26mm has been grown by slow cooling (Low Temperature Solution) method. The grown crystals were subjected to various characterization studies such as chemical etching, UV–vis spectrum, birefringence, laser damage threshold, Photoluminescence studies and second harmonic generation studies. The quality was ascertained by birefringence studies. Piezoelectric charge coefficients of the grown crystal have been determined. The dielectric constant, dielectric loss and ac conductivity of the compound were calculated at different temperatures and frequencies to analyze the electrical properties.

Dual-functional zinc oxide aggregates with reaction time-dependent morphology as the dye-adsorption layer for dye-sensitized solar cells

Abstract High surface area and light scattering abilities are dispensable for a well-performed photoanode of dye-sensitized solar cells (DSSCs) to respectively provide abundant active sites for dye adsorption and enhance the light path for electron excitation. In this study, an energy-saving and cost-effective low-temperature (80 °C) aqueous solution method is applied to synthesize dual-functional ZnO aggregates which are composed of small nanocrystallites with the diameter of 20 nm. The reaction time plays a significant role in controlling the morphology of ZnO nanostructures. The ZnO aggregates are randomly oriented at the early stage and the flower-like morphology gradually forms when the reaction time reaches 4 h, while the well-defined structure is further destroyed when the reaction time is increased to 8 h. The growth mechanism is proposed to discuss the formation of ZnO nanoflower. The ZnO nanoflower-based DSSC achieves a light-to-electricity conversion efficiency (η) of 4.41%, which is higher than that for the cell with commercial ZnO nanoparticles on its photoanode (3.42%) under AM 1.5G simulated sunlight with an intensity of 100 mW/cm2. The electrochemical impedance spectroscopy (EIS) is also applied to analyze the electron transport parameters to understand the kinetics of electron transport in the ZnO films. The low-temperature (150 °C) fabrication process for preparing the highly-performed ZnO film also enables the future applications of flexible DSSCs with polymeric substrates.

Non-aqueous synthesis of blue light emitting γ-Ga2O3 and c-In2O3 nanostructures from their ethylene glycolate precursors

A simple, low temperature solution method is reported for the synthesis of metastable crystalline cubic γ-Ga2O3 nanorods and cubic In2O3 nanoparticles having good size and shape uniformity, starting from their ethylene glycolate precursors. The crystal structure, morphology and sizes of the nanostructures have been determined by X-ray diffraction (XRD) and high-resolution transmission spectroscopy (HRTEM). The optical properties of the nanostructures have been explored by measuring room temperature photoluminescence spectra. Ga2O3 nanorods exhibit photoluminescence (PL) in blue region, arising from donor–acceptor recombination. The PL spectrum of In2O3 nanoparticles shows strong bands in the blue region as well as a weak band in green region which can be ascribed to presence of oxygen vacancies. The favorable structural and optical properties suggest their scope for blue light-emitting applications.