Low-Temperature Processed Brookite Interfacial Modification for Perovskite Solar Cells with Improved Performance.

The scaffold layer plays an important role in transporting electrons and preventing carrier recombination in mesoporous perovskite solar cells (PSCs), so the engineering of the interface between the scaffold layer and the light absorption layer has attracted widespread concern. In this work, vertically grown TiO2 nanorods (NRs) as scaffold layers are fabricated and further treated with TiCl4 aqueous solution. It can be found that a thin brookite TiO2 nanoparticle (NP) layer is formed by the chemical bath deposition (CBD) method on the surface of every rutile NR with a low annealing temperature (150 °C), which is beneficial for the infiltration and growth of perovskite. The PSC based on the TiO2 NR/brookite NP structure shows the best power conversion of 15.2%, which is 56.37% higher than that of the PSC based on bare NRs (9.72%). This complex structure presents an improved pore filling fraction and better carrier transport capability with less trap-assisted carrier recombination. In addition, low-annealing-temperature-formed brookite NPs possess a more suitable edge potential for electrons to transport from the perovskite layer to the electron collection layer when compared with high-annealing-temperature-formed anatase NPs. The brookite phase TiO2 fabricated at a low temperature presents great potential for flexible PSCs.

Fabrication of Porous Lead Bromide Films by Introducing Indium Tribromide for Efficient Inorganic CsPbBr3 Perovskite Solar Cells.

In the process of preparing CsPbBr3 films by two-step or multi-step methods, due to the low solubility of CsBr in organic solvents, the prepared perovskite films often have a large number of holes, which is definitely not conducive to the performance of CsPbBr3 perovskite solar cells (PSCs). In response to this problem, this article proposed a method of introducing InBr3 into the PbBr2 precursor to prepare a porous PbBr2 film to increase the reaction efficiency between CsBr and PbBr2 and achieve the purpose of In (Ⅲ) incorporation, which not only optimized the morphology of the produced CsPbBr3 film but also enhanced the charge extraction and transport capabilities, which was ascribed to the reduction of the trap state density and impurity phases in the perovskite films, improving the performance of CsPbBr3 PSCs. At the optimal InBr3 concentration of 0.21 M, the InBr3:CsPbBr3 perovskite solar cell exhibited a power conversion efficiency of 6.48%, which was significantly higher than that of the pristine device.

Au/CdS Core-Shell Sensitized Actinomorphic Flower-Like ZnO Nanorods for Enhanced Photocatalytic Water Splitting Performance.

Herein, a novel actinomorphic flower-like ZnO/Au/CdS nanorods ternary composite photocatalyst is prepared to extend the light-responsive range, reduce the photogenerated charge carriers recombination, and ultimately improve the water splitting performance. Flower-like ZnO nanorods are synthesized by a chemical bath method and the CdS nanoparticles are sensitized by successive ionic layer adsorption and reaction method. Then the Au nanoparticles as co-catalysts are introduced by the photodeposition method to modify the interface of ZnO/CdS for reducing the photogenerated electron recombination rate and further improving the performance of water splitting. Detailed characterizations and measurements are employed to analyse the crystallinity, morphology, composition, and optical properties of the flower-like ZnO/Au/CdS nanorods samples. As a result, the flower-like ZnO/Au/CdS nanorod samples present significantly enhanced water splitting performance with a high gas evolution rate of 502.2 µmol/g/h, which is about 22.5 and 1.5 times higher than that of the pure ZnO sample and ZnO/CdS sample. The results demonstrate that the flower-like ZnO/Au/CdS nanorods ternary composite materials have great application potential in photocatalytic water splitting for the hydrogen evolution field.

Interfacial Modification of Mesoporous TiO2 Films with PbI2-Ethanolamine-Dimethyl Sulfoxide Solution for CsPbIBr2 Perovskite Solar Cells.

As one of the most frequently-used electron-transporting materials, the mesoporous titanium dioxide (m-TiO2) film used in mesoporous structured perovskite solar cells (PSCs) can be employed for the scaffold of the perovskite film and as a pathway for electron transport, and the contact area between the perovskite and m-TiO2 directly determines the comprehensive performance of the PSCs. Because of the substandard interface combining quality between the all-inorganic perovskite CsPbIBr2 and m-TiO2, the development of the mesoporous structured CsPbIBr2 PSCs synthesized by the one-step method is severely limited. Here, we used a solution containing PbI2, monoethanolamine (EA) and dimethyl sulfoxide (DMSO) (PED) as the interfacial modifier to enhance the contact area and modify the m-TiO2/CsPbIBr2 contact characteristics. Comparatively, the performance of the solar device based on the PED-modified m-TiO2 layer has improved considerably, and its power conversion efficiency is up to 6.39%.

Incorporation of Nickel Ions to Enhance Integrity and Stability of Perovskite Crystal Lattice for High-Performance Planar Heterojunction Solar Cells.

Enhancement of integrity and stability of crystal lattice are highly challenging for polycrystalline perovskite films. In this work, a strategy of incorporation of nickel (Ni) ions is presented to modulate the crystal structure of the CH3NH3PbI3 perovskite film. A broad range of experimental characterizations reveal that the incorporation of Ni ions can substantially eliminate the intrinsic halide vacancy defects, since Ni ions have a strong preference for octahedral coordination with halide ions, resulting in significantly improved integrity and short-range order of crystal lattice. Moreover, it is also demonstrated that the stronger chemical bonding interaction between Ni ions and halide ions as well as organic group can improve the stability of the perovskite material. Simultaneously, the surface morphology of the perovskite thin film is also improved by the incorporation of nickel ions. As a result, a planar heterojunction perovskite solar cell incorporated with 1.5% Ni exhibits a power conversion efficiency of 18.82%, which is improved by 25% compared with 14.92% for the pristine device. Simultaneously, the device formed incorpration of 1.5% Ni shows remarkable stability with 90% of the initial efficiency after storage in an air environment for 800 h. The studies provide a new insight into metal-incorporated perovskite materials for various optoelectronic applications.

Highly stable hole-conductor-free perovskite solar cells based upon ammonium chloride and a carbon electrode.

Organic-inorganic hybrid perovskite solar cells (PSCs) have become a research hotspot due to the impressive photovoltaic performance. The perovskite film plays an extremely important role in the light-to-electricity conversion, meanwhile, the stability of PSCs is also an important factor affecting the application of devices. Here we demonstrate a kind of stable PSCs by using simple solution-process in an air enviroment with about 45% relative humidity. Firstly, the NH4Cl was added to the perovskite precursor solution to adjust the kinetics of crystallization and growth of active layer, and then obtain high-quality CH3NH3PbI3 perovskite films. Hydrophobic carbon electrode was used to protect the perovskite active layers and further improve the stability of PSCs, which optimized the structure of the devices at the same time. We adjusted the amount of NH4Cl in the perovskite precursor solution (PbI2: CH3NH3I: NH4Cl = 1: 1: x (x = 0 ∼ 1), and investigated the effect of that on the properties of perovskite active layers and PSCs. The above results showed that the devices achieved fully covered perovskite thin films and improved the photovoltaic performance of PSCs when the NH4Cl additive was x  = 0.8. The short-circuit current density (Jsc), fill factor (FF) and power conversion efficiency (PCE) were significantly enhenced. Under the condition of ambient air and no encapsulation, the PSCs exhibited good stability after 576 h test, and the PCE was still about 96% of the initial efficiency.

Enhanced photovoltaic properties of perovskite solar cells by TiO2 homogeneous hybrid structure.

In this paper, we fabricated a TiO2 homogeneous hybrid structure for application in perovskite solar cells (PSCs) under ambient conditions. Under the standard air mass 1.5 global (AM 1.5G) illumination, PSCs based on homogeneous hybrid structure present a maximum power conversion efficiency of 5.39% which is higher than that of pure TiO2 nanosheets. The enhanced properties can be explained by the better contact of TiO2 nanosheets/nanoparticles with CH3NH3PbI3 and fewer pinholes in electron transport materials. The advent of such unique structure opens up new avenues for the future development of high-efficiency photovoltaic cells.

Embedded vertically aligned cadmium telluride nanorod arrays grown by one-step electrodeposition for enhanced energy conversion efficiency in three-dimensional nanostructured solar cells.

Vertically aligned CdTe nanorods (NRs) arrays are successfully grown by a simple one-step and template-free electrodeposition method, and then embedded in the CdS window layer to form a novel three-dimensional (3D) heterostructure on flexible substrates. The parameters of electrodeposition such as deposition potential and pH of the solution are varied to analyze their important role in the formation of high quality CdTe NRs arrays. The photovoltaic conversion efficiency of the solar cell based on the 3D heterojunction structure is studied in detail. In comparison with the standard planar heterojunction solar cell, the 3D heterojunction solar cell exhibits better photovoltaic performance, which can be attributed to its enhanced optical absorption ability, increased heterojunction area and improved charge carrier transport. The better photoelectric property of the 3D heterojunction solar cell suggests great application potential in thin film solar cells, and the simple electrodeposition process represents a promising technique for large-scale fabrication of other nanostructured solar energy conversion devices.

Synthesis of uniform cadmium sulphide thin film by the homogeneous precipitation method on cadmium telluride nanorods and its application in three-dimensional heterojunction flexible solar cells.

High-density CdTe nanorod arrays are successfully embedded in a uniform and compact CdS layer, forming a novel three-dimensional (3D) CdTe NRs/CdS heterojunction structure. The CdS layer is prepared by homogeneous precipitation (HP) method using decomposition of urea. The effects of temperature and concentration of reactants on the growth and composition of CdS film are investigated in detail. The results demonstrate that the temperature affects the thermal decomposition of urea significantly, and the concentration of CdCl2 and CS (NH2)2 plays an essential role in the compositional ratio of CdS film. Further investigations reveal that, in comparison with the traditional precipitation method, a better coverage of CdS on the surface of CdTe NRs can be obtained by HP method due to the slow and even hydrolysis of urea. Moreover, photovoltaic performance of the novel CdTe NRs/CdS 3D photovoltaic device is also investigated. This study demonstrates that the 3D heterostructure has potential application in thin film solar cells, and the successful deposition of CdS layer on the surface of CdTe NRs by HP method suggests a promising technique for large-scale fabrication of these solar cells.

Effect of sintering temperature on the luminescence properties of Ca0.8Ba0.2TiO3:Pr(3+) red-emitting phosphor.

Nanoparticles with the nominal composition Ca0.8Ba0.2Ti03:Pr(3+) were prepared using the sol-gel process. Barium nitrate, 4-hydrated calcium nitrate and praseodymium oxide were used as raw materials. The structural evolution and decomposition processes of the precursors were investigated by powder X-ray diffraction, differential thermal analysis and thermogravimetric analysis. Crystalline Ca0.8Ba0.2Ti03:Pr(3+) could be obtained at 700°C. The photoluminescence properties of the samples were investigated using excitation and emission spectra. Ca0.8Ba0.2Ti03:Pr(3+) nanoparticles showed strong red emission, which could be assigned to the typical (1) D2 →(3) H4 transition of Pr(3+). Furthermore, the study found that sintering temperature and the introduction of Ba(2+) influence the decay time of persistent luminescence.

Enhanced photoelectric performance of PbS/CdS quantum dot co-sensitized solar cells via hydrogenated TiO2 nanorod arrays.

The enhanced photoelectric performance of quantum dot sensitized solar cells via hydrogenated TiO2 is proposed. The best energy conversion efficiency is 1.5 times higher than cells without hydrogen treatment. We demonstrated that introducing oxygen vacancies by hydrogenation is an effective and feasible method for enhanced photoelectric performance.

ZnO nanorod array/CuAlO2 nanofiber heterojunction on Ni substrate: synthesis and photoelectrochemical properties.

A novel ZnO nanorod array (NR)/CuAlO(2) nanofiber (NF) heterojunction nanostructure was grown on a substrate of Ni plates using sol-gel synthesis for the NFs and hydrothermal reaction for the NRs. Compared with a traditional ZnO/CuAlO(2) laminar film nanostructure, the photocurrent of this fibrous network heterojunction is significantly increased. A significant blue-shift of the absorption edge and a favorable forward current to reverse current ratio at applied voltages of -2 to +2 V were observed in this heterojunction with the increase of Zn(2+) ion concentration in the hydrothermal reaction. Furthermore, the photoelectrochemical properties were investigated and the highest photocurrent of 3.1 mA cm(-2) was obtained under AM 1.5 illumination with 100 mW cm(-2) light intensity at 0.71 V (versus Ag/AgCl). This novel 3D fibrous network nanostructure plays an important role in the optoelectronic field and can be extended to other binary or ternary oxide compositions for various applications.

Large-scale synthesis and microwave absorption enhancement of actinomorphic tubular ZnO/CoFe2O4 nanocomposites.

Actinomorphic tubular ZnO/CoFe(2)O(4) nanocomposites were fabricated in large scale via a simple solution method at low temperature. The phase structures, morphologies, particle size, shell thickness, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). The as-synthesized nanocomposites were uniformly dispersed into the phenolic resin then the mixture was pasted on metal plate with the area of 200 mm x 200 mm as the microwave absorption test plate. The test of microwave absorption was carried out by the radar-absorbing materials (RAM) reflectivity far field radar cross-section (RCS) method. The range of microwave absorption is from 2 to 18 Hz and the best microwave absorption reach to 28.2 dB at 8.5 Hz. The results indicate that the composites are of excellence with respect to microwave absorption.

Ultrasonic-assisted synthesis of highly dispersed MoO3 nanospheres using 3-mercaptopropyltrimethoxysilane.

With ultrasonic irradiation as assistance, highly dispersed MoO(3) nanospheres were synthesized using silane coupling agent 3-mercaptopropyltrimethoxysilane HS-(CH(2))(3)Si(OCH(3))(3) (MPTS) as figuration agent. The results of X-ray powder diffractometer (XRD) showed that the precursor was hexagonal molybdenum oxide hydrate (MoO(3).0.55H(2)O). It was converted into orthorhombic MoO(3) after annealed at 400 degrees C for 2h. Transmission electron microscopy (TEM) showed that MoO(3).0.55H(2)O and MoO(3) nanoparticles were spherical with particle-size distribution of ca. 30-80 nm and 25-75 nm, respectively. Results indicated that MPTS and ultrasonic irradiation played important role in formation of highly dispersed MoO(3) nanospheres. X-ray photoelectron spectroscopy (XPS) was also adopted to confirm the growth mechanism. The possible cause of formation was based on dispersion function of ultrasonic irradiation and figuration of MPTS.

Growth of dumbbell-like ZnO microcrystals under mild conditions and their photoluminescence properties.

Large-scale uniform dumbbell-like ZnO microcrystals were successfully synthesized via a facile solution method under mild conditions. The as-prepared dumbbells, with lengths of 3.5-5.4 microm and diameters of 1.3-1.8 microm, possess a single-crystal hexagonal structure and grow along the [0001] direction. The influence of the reactant concentration on the size and shapes of the ZnO samples had been studied, and the results revealed that the reactant concentration plays a crucial role in determining final morphologies of the samples. Moreover, the evolution process of the dumbbell-like ZnO microcrystals was viewed by field-emission scanning electron microscopy (FE-SEM) characterization, and a possible formation mechanism was proposed. In addition, optical properties of the ZnO samples prepared at different reaction times were also investigated by photoluminescence (PL) spectroscopy. The room-temperature PL spectrum of the dumbbell-like ZnO microcrystals shows a strong UV emission peak. The UV emission is further identified to originate from the radiative free-exciton recombination by the temperature-dependent PL.