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More and more attention has been paid to CsPbIBr2 material for perovskite solar cells (PSCs), owing to the trade-off between bandgap and stability. However, the reported maximum power conversion efficiency (PCE) of CsPbIBr2 PSCs is lag behind that of the congeners due to the serious interface recombination of charge carriers. In this work, the effects of interface defect density and interface band offset on the properties of CsPbIBr2 PSCs are investigated. It is found that the characteristic of the front electron transfer layer (ETL)/perovskite interface has a significant influence on the performance of PSCs than that of the back perovskite/hole transfer layer (HTL) interface. Additionally, a PCE of 15.05% with a high open-circuit voltage (VOC) of 1.54 V is obtained for the PSCs with FTO/ZnOS/CsPbIBr2/CuAlO2/Au structure. Finally, two-terminal monolithic all-perovskite double-junction tandem solar cells (TSCs) with the architecture of FTO/ZnOS/CsPbIBr2/CuAlO2/ITO/TiO2/MAPbI3/Spiro-MeOTAD/Au are constructed, and a maximum PCE of 27.4% (VOC of 2.60 V, JSC of 12.21 mA/cm2, and FF of 86.42%) is obtained for the TSCs with top and bottom absorber thicknesses of 600 nm and 500 nm respectively. Furthermore, four-terminal triple-junction TSCs are designed with silicon solar cells as bottom sub-cell, and a maximum PCE of 35.35% is achieved. These results will provide theoretical guidance for the fabrication of high performance TSCs.

It is well known that the phase stability of CsPb(I1−xBrx)3 (0 ≤ x ≤ 1) perovskite materials is enhanced under humid environments with the increase of Br− concentration in film, however, the bandgap (Eg) is also widened synchronously, resulted in limiting the light harvesting and then reducing the power conversion efficiency (PCE) of devices. Hence, how to realize the compatibility of high stability and high PCE is a challenge for device based on CsPb(I1−xBrx)3. In this work, the two- (2-T) and four-terminal (4-T) tandem solar cells (TSCs) consisting of a CsPb(I1−xBrx)3 top sub-cell and a crystalline silicon (c-Si) bottom sub-cell are constructed and compared. It is found that in the case of 2-T configuration, performance of device is very sensitive to the Eg and the thickness of top sub-cell, and a maximum PCE of 29.23% is achieved only for the CsPbI3 top sub-cell at an optimum thickness of 275 nm. However, in the 4-T formation, devices present a weak dependence on the Eg and the thickness of top sub-cell, and PCEs above 28.5% can be obtained when CsPbBr3 is used as top sub-cell. These results highly underline the application potential of 4-T CsPb(I1−xBrx)3/Si TSCs, especially for CsPbBr3/Si TSC.

In recent years, inorganic CsPbBr3-based perovskites have accomplished considerable progress owing to their superior stability under harsh humid environment. The power conversion efficiency (PCE) of CsPbBr3 perovskite solar cells (PSCs) has seen an unprecedented development from 5.74% to 10.91% with the improvement of the CsPbBr3 crystal quality. Despite extensive research efforts, the device efficiency of the CsPbBr3-based PSCs still lags behind that of other hybrid perovskite materials. Therefore, there is a significant interest in further boosting the performance of all-inorganic CsPbBr3 PSCs by the synergic optimization of films and device interfaces. In this review, we have discussed and summarized recent advances and methodologies related to CsPbBr3 films and PSCs. Furthermore, we discuss different fabrication strategies such as solution-based and vapor-based methods and their influence on the properties of CsPbBr3, particularly the morphology of films. Moreover, the timeline of improvement of the device efficiency from 2015 to 2020 is comprehensively addressed and developments are clearly sorted out by addressing critical factors influencing the photovoltaic performance. We further highlight state-of-the-art engineering strategies for CsPbBr3 PSCs that facilitate the crystallization control, charge extraction, suppression of charge recombination, and defect passivation in a systematic manner. At the end of the review, the summary and perspectives are presented along with beneficial guidelines for developing highly efficient and stable CsPbBr3 PSCs.

Recently, inorganic perovskite solar cells (PSCs) based on CsPbBr3 have triggered incredible interest due to the demonstrated excellent stability against thermal and high humidity environmental conditions. However, the power conversion efficiency (PCE) of the CsPbBr3-based PSCs is still lower than that of the organic-inorganic hybrid one, because of the large band gap and serious charge recombination at the interface or inside the device. Here, the working mechanism of the devices with normal n-i-p planar structure is modeled and investigated using SCAPS 1D simulation software. The simulation results state that the proper band structure of PSCs is crucial to carrier separation and transport. The high interface recombination, originated from the large band offsets of the electron transport material (ETM)/absorber and absorber/hole transport material (HTM) respectively, can be effectively diminished with the continuous gradient junction design of the absorber, and a PCE of 11.58% is obtained with a high open-circuit voltage (VOC) of 1.68 V. Moreover, by building a heterojunction bilayer absorption scenario of CsPbIBr2/CsPbBr3 and employing ZnOS and Cu2ZnSnS4 films as the ETM and HTM respectively, the PCE of PSCs is further increased to 15.89%, caused mainly by the enhancement in short-current density (JSC). Moreover, reducing the interface defect density is also very important to improve the performance of PSCs. These results will provide theoretical guidance for improving the performance of the CsPbBr3-based PSCs.

Unique optical, electrical and chemical properties make carbon nanotubes (CNTs) an excellent candidate for potential applications in the next-generation optoelectronics. Especially, the optoelectronic properties of CNTs can be enhanced dramatically by constructing heterostructures with other materials, in which the charge separation efficiency is enhanced and the recombination probability of excitons is suppressed significantly. Therefore, the CNT-based heterostructures have been widely used as active materials in high-performance photoelectronic devices. Herein, the recent progress of the CNT-based heterostructure photodetectors is reviewed. Firstly, the working mechanisms and typical figures-of-merits are introduced. Secondly, different type CNT-based heterostructures and related photodetectors are highlighted, such as van der Waals heterostructures, all-carbon heterostructures, and bulk heterostructures. Finally, we give the current challenges and future prospects for the development of this emerging field.

Formamidinium tin iodide (FASnI3), as one promising Pb-free halide perovskite, has received extensive attention. But perovskite solar cells (PSCs) based on FASnI3 films have yet to realize the high power conversion efficiency (PCE) achieved in its Pb-based counterparts. To investigate the limitation of FASnI3-based perovskite solar cells with inverted p-i-n planar structures, the influences of various parameters on the device performance are analyzed through device simulation. The results reveal that defect density at front hole transport material (HTM)/absorber interface is critical for high efficiency. And it is interesting to note that the doping density, rather than the doping type and its space distribution, dominates the device properties, and an upper limit of 1 × 1016 cm−3 is achieved. In addition, the response of device to band offset is investigated, and an optimum electron affinity of 3.9 eV is obtained. Finally, the effects of relative permittivity and thickness of the absorber with different carrier lifetime are studied. A maximum PCE of 9.75% is achieved at absorber thickness of 300 nm with carrier lifetime of 0.1 ns? These results show that optimizing the interface property and band offset, improving the stability of Sn2+ and reducing the defect density of absorber layer are the main challenges for high-performance FASnI3-based PSCs in the future research.

Owing to the inevitability of moisture/thermal instability in organic-inorganic hybrid perovskites, pure inorganic perovskites such as CsPbI2Br perovskite have surfaced as promising options for commercial perovskite solar cells (PSCs) due to their high photovoltaic performance and excellent inherent stability. However, designing additive engineering approaches to mitigate defect-induced crystalline phase transitions from a photosensitive perovskite phase to a non-perovskite phase has been a difficult task for researchers. In this work, using a one-step spin coating approach, we have prepared a polyvinylpyrrolidone (PVP) polymer-incorporated stable phase of CsPbI2Br at a low temperature (120 ​°C). Examinations using structural, morphological, and photo-physical measurements revealed that the optimum amount of PVP can greatly improve the optoelectronic properties of the film, which facilitates in reducing the trap states and defect in perovskite film, thus enabling charge carrier separation and suppressing charge recombination. As a result, the device based on 5 ​mg-PVP achieves a champion power conversion efficiency (PCE) of 10.47%, with a fill factor (FF) of 56.35%, a short-circuit current (JSC) of 18.47 ​mA ​cm2, and an open-circuit voltage (VOC) of 1.01 ​V, which is significantly higher than the device without PVP (6.36%). These findings suggest that PVP-CsPbI2Br has tremendous promise for future research and application in photovoltaic devices.

Since the first report in 2009, the certified power conversion efficiency (PCE) of organic-inorganic halide perovskite solar cells (PSCs) has rapidly risen to 23.3%, which successfully demonstrates the importance of film morphology and quality management, especially for the planar heterojunction architecture based on solution-processed method. In this paper, the morphology, structure, optical and electrical properties of perovskite films treated by two different multi-step thermal annealing methods have been studied and compared. For the conventional multi-step (CMS) annealing method, the surface morphologies and optical properties of films are significantly influenced by the annealing temperature due to the decomposition of CH3NH3PbI3. When the modified multi-step (MMS) method is adopted, the decomposition of CH3NH3PbI3 can be effectively suppressed. The best device treated by MMS method at 180 °C showed a short circuit current density of 20.85 mA/cm2, an open circuit voltage of 0.96 V, a fill factor of 72.7%, and a PCE of 14.7%, which is a 23.5% enhancement in PCE relative to the maximum 11.9% treated by CMS method at 160 °C. These findings suggest that the efficiency of PSCs can be further improved by optimizing the preparation process.

In this paper, we present a successful partial substitution of PbI2 by a much less expensive and toxic FeCl2 in perovskite films, namely MAI(PbI2)1−x(FeCl2)x (MA = CH3NH3+), and the followed effects on the performance of planar heterojunction perovskite solar cells (PSCs). The incorporation of a small content of Fe and Cl ions into the perovskite films could improve the growth morphology, enhance the crystallinity, increase the carrier lifetimes, as well as tune the material work function and Fermi level without significantly changing the band gap. Consequently, by adjusting the FeCl2 substitution fraction into the perovskite films, a power conversion efficiency above 17% is achieved with a high open-circuit voltage up to 1.10 V. Our work implies that conventional chlorides as substituting material of PbI2 have huge potential for the fabrication of more ecological PSCs.

Due to its outstanding stability, all-inorganic cesium lead bromide (CsPbBr3) perovskite is gaining increasing attention as a functional material in photovoltaics and other optoelectronic applications. However, the preparation of high-quality CsPbBr3 films via solution processing remains a significant challenge due to the cesium precursor’s low solubility in common solvents. As a result, developing viable evaporation deposition strategies is critical for increasing the photovoltaic performance of perovskite solar cells (PSCs) based on CsPbBr3. In this paper, a modified hybrid chemical vapor deposition is applied to fabricate CsPbBr3 films, and the effects of reaction temperature and reaction time on the crystallinity, morphology, and photo-electric properties of the films are investigated. By optimizing the reaction conditions, high-quality CsPbBr3 films with good crystallinity and uniformity are successfully obtained. Based on these films, CsPbBr3 PSCs with a device configuration of fluorine-doped tin oxide/compact-TiO2/CsPbBr3/carbon attained impressive power conversion efficiency of 4.41% with an ultra-high open-circuit voltage (V OC) of 1.39 V. This demonstration suggests that the modified hybrid chemical vapor deposition strategy enables a promising fabrication route suitable for all-inorganic perovskite thin films in photovoltaic application.

Inorganic perovskites (CsPbX3, X = I−, Br− or Cl−) have got researchers attention in the photovoltaic community due to their exceptional photoelectric properties and high thermal stability. In this work, we have explained a two-step vapor deposition approach to fabricate the CsPbCl3 films. To improve the properties of CsPbCl3 perovskite, different reaction conditions and their influence on the structural, morphological and optical properties of resultant films were systematically examined. We found that the proposed deposition strategy has a wide reaction window and is viable for the preparation of uniform CsPbCl3 films. The optimal reaction conditions resulted in improved crystallinity, morphology and photoluminescence. The present work will provide beneficial guidance for high-quality CsPbCl3 and other CsPbX3 perovskite films for future optoelectronic applications.

Organic–inorganic hybrid perovskite solar cells have made great breakthroughs in the past few years, and spurred researchers to develop and experiment a variety of new architectures. One-dimensional nanostructures are naturally introduced in solar cells, because of their excellent charge transport properties and open-pore structure. However, the performances of these solar cells are inferior to their mesoporous counterparts, suggesting that some unique mechanisms maybe held behind devices operation. Here, a three-dimensional optical model combined with a two-dimensional axisymmetric semiconductor model is applied to investigate the influence of the architectural design of scaffolds on the properties of perovskite solar cells based on Al2O3 nanorod arrays. Simulation results show a great dependence of device performance on the density, length and porosity of Al2O3 nanorods, which decided the electron field distribution and carrier recombination loss inside the cells. Strikingly, an optimal length of 450 nm for Al2O3 nanorods is obtained for the perovskite solar cells with efficiency over 20% at porosity of 0.7. The results obtained have some guidance function on the fabrication of high efficiency PSCs based on nanorods.

CsPbI3 perovskite materials have triggered enormous research attention as promising light-harvesting or fluorescent materials, owing to their high photoluminescence quantum yields, narrow photoluminescence (PL) emission spectra and excellent photophysical properties based on the quantum confinement effect. However, the formation of desirable black-phase CsPbI3 requires complex processing at higher annealing temperatures and upon formation it suffers from instability issues at room temperature, hindering its potential for optoelectronic application. In this work, using polyvinylpyrrolidone (PVP) as an additive, highly stable CsPbI3 nanocrystalline films are prepared at a low annealing temperature of 180 °C via a one-step spin-coating method. It is found that the PVP additive not only improves the stability by inhibiting the transition of CsPbI3 from α- to δ-phase at room temperature but also influences the crystallization dynamics. In addition, the PL intensity is substantially enhanced due to the suppression of non-recombination sites with PVP. With a PVP concentration of 12 wt%, a charge carrier lifetime of 43.99 ns is obtained and a palpable orange-yellow color is formed irradiated in plane by a green laser. Finally, a simple photodetector is fabricated with a structure of FTO/PVP-CsPbI3/Ag, exhibiting excellent photodetecting response with increased PVP concentration in the film. These results suggest that PVP-CsPbI3 has strong research and application potential in the future in optoelectronic devices.

As potential candidates for organic–inorganic hybrid perovskite materials, Pb-free Cs2SnI6 has gained considerable attention because of their better stability under atmospheric conditions containing oxygen and water vapor. Herein, we fabricate Cs2SnI6 films using the vapor-assisted deposition method with Sn and I2 powders as reactants. To obtain uniform and pure Cs2SnI6 films, two different reaction systems are applied and the properties of the samples are characterized via x-ray diffraction, scanning electron microscopy, UV–vis spectrometer, photoluminescence, and Hall-effect measurements. All the results showed a strong dependency on the reaction temperature and fabrication approach. Based on the preparation process in a closed system, we successfully inhibited the high temperature decomposition of Cs2SnI6 even at 250 °C. However, in the open system, the reaction temperature of Cs2SnI6 films should not be higher than 200 °C. Finally, n-type semiconducting Cs2SnI6 films with bandgap (E g) of 1.32–1.54 eV, carrier concentration of 1013–1016 cm−3, and carrier mobility above 100 cm2 V−1 s−1 are obtained due to the generated I-rich synthesis condition. We believe that our findings will provide beneficial guidance for the fabrication of Cs2SnI6 perovskite solar cells.

In this work, we investigate the electronic and optical properties of CsPb(I1-xBrx)3 and CsSn(I1-xBrx)3 by using density functional theory. We have proposed the method of strain modulation to efficiently tune the bandgap of CsPb(I1-xBrx)3 and CsSn(I1-xBrx)3 perovskites. Our calculations show that, the bandgap of CsPbI3 can be successfully tuned with the strain variation of −3% to 3%. Furthermore, the electronic structure changes of CsPb(I1-xBrx)3 and CsSn(I1-xBrx)3 with Br concentration, the higher the Br doping concentration, the higher will be the energy band value. We believe that the effective regulation of the energy bandgap can fulfill the requirements of a promising light-harvesting material.

Plasmonics is a new promising approach to enhance the light absorption in the thin film solar cells. The plasmonic effects of the metal nanoparticle introduced in thin film solar cells could also be detrimental for the higher optical absorption and hence the higher efficiency of solar cells. The effects of the Ag nanospheres arrays on the absorption of amorphous silicon solar cells were investigated by a numerical simulation based on the finite element method. The light absorption under different radius and width of the grating has been calculated. The optimization results show that the absorption of the solar cell with Ag nanospheres is enhanced up to 64 % under AM1.5 illumination in the 500–730 nm wavelength range compared with the reference cell. The physical mechanisms of absorption enhancement in different wavelength range have been discussed. These results are promising for the design of amorphous silicon thin film solar cells with enhanced performance.

Organo-metal halide perovskite solar cells have shown unique charms in the upgrade rate of maximum power conversion efficiency, the diversity of device architecture and facilitated fabrication process. And the clear understanding of the role of each component and the basic working mechanisms in solar cells is important for further improvement in efficiency, especially for mesoscopic perovskite solar cells. Here, a two-dimensional modeling of the TiO 2 nanowire-based organic–inorganic hybrid perovskite solar cells was performed combining the optical and electrical responses to reveal the impact of the properties of TiO 2 nanowire array and absorber layer. Simulation results show a great dependence of device performance on the electron concentration of TiO 2 nanowires, which decided the electron field distribution inside cells, and an optimum thickness of 600 nm is obtained for the TiO 2 nanowires with low electron concentration. The collection of carriers is primarily within perovskite itself, and the ratio through TiO 2 nanowire is less than 5%. These findings can facilitate device optimization and enhance the performance of the perovskite solar cells.

The scattering from metal nanoparticles near their localized surface plasmon resonance is a promising way to increase the light absorption in solar cells. In this article, we investigate the light scattering of silver (Ag) nanoparticles on the microcrystalline silicon (μc-Si) substrate with various sizes and shape by finite element method. The results show that large spherical particles lead to enhanced scattering efficiency, whereas reduced coupling efficiency. The scattering cross section and coupling efficiency are very sensitive to the shape of the particles. Compared with spherical particles, hemispherical and cylindrical particles show much lower and broader scattering cross section, containing two surface plasmon resonance modes, and much higher coupling efficiency at longer wavelengths. However, with the increase in the longitudinal size (or height) of the particles, the coupling efficiency decreases, especially at shorter wavelengths, due to backscattering by the longitudinal resonance mode. Finally, we simulate the absorption enhancement in μc-Si thin film solar cells by Ag nanoparticle arrays with various shape. These results will be useful for enhancing performance of the μc-Si thin film solar cells by optimizing the light-trapping design.

Recently, organo–metal halide perovskites have attracted much attention of the scientific community relating to their successful application in the absorber layer of low-cost solar cells. However, enough is known about the material and device properties, to realize that much remains to be learned. In this study, a two-dimensional modeling of planar heterojunction perovskite solar cells was performed combining the optical and electrical responses to reveal the impact of the carrier diffusion length, the relative permittivity of absorber layer and the valence band offset of absorber/hole transport material (HTM). Simulation results presented a great dependence of power conversion efficiency (PCE) on the carrier diffusion length of perovskite layer. Meanwhile, to achieve high PCE, the frequency depended dielectric constant should not exceeded 40 and the double HTMs design was very effective to match the valence bands between the absorber and HTM.

In recent years, the organic-inorganic perovskite materials have revolutionized the Photovoltaic industry with highly efficient power conversion devices accompanied by a high growth rate. However, these devices experience major environmental and stability issues that hinder their true potential. More recently, a rarely studied perovskite material Cs2SnI6 is gaining enormous attention due to its superior stability and suitable bandgap. In this work, we developed a modified two-step process to prepare uniform Cs2SnI6 films, and the influence of the reaction conditions on the properties is explored. The structural, morphological, optical, and electrical properties of the prepared films were investigated using x-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV–vis spectrometer, photoluminescence, and Hall Effect measurements, respectively. Phase stability and morphology of the films are improved with optimizing the reaction conditions. The results confirm the n-type semiconductor nature of Cs2SnI6 with bandgap ranging from 1.29 eV to 1.42 eV with maximum carrier mobility of 425 cm2 V−1 s−1. The present study will further provide potential research directions in improving the device efficiency of air-stable Cs2SnI6 perovskite solar cells.

Practicability of CsSnI3 has been limited by the lack of stability in humid environment. Here we calculated phase stability, the impact of H2O embedded in CsSnI3 and surface adsorption by the first-principles calculations. Total energy results show that γ-CsSnI3 and Y-CsSnI3 are more stable. However, the γ-CsSnI3 is hydrophilic-like and Y-CsSnI3 is hydrophobic-like. Further studies show that H2O tend to adsorb at the hollow sites on the (001) surface. The strong coupling between O and Cs atoms and hydrogen bonding render the deformation of (001) surface. These results are partially explained the phase instability of perovskites in air.

The SnO thin films have been deposited on quartz glass substrates using an e-beam evaporation system at room temperature and different post-deposition thermal treatments have been carried out. In case of annealing in air, n-type polycrystalline SnO films are obtained after annealing at 300 °C and 400 °C, respectively. For the 500 °C annealed film, SnO2 phase is generated due to the strong oxidation. However, when annealed in vacuum, pure p-type polycrystalline SnO films are produced. The feasible and controllable methods of p- and n-type SnO films contributes to the development of high performance devices.

Light trapping is one of the key issues to improve the light absorption and increase the efficiency of thin film solar cells. The effects of the triangular Ag nanograting on the absorption of amorphous silicon solar cells were investigated by a numerical simulation based on the finite element method. The light absorption under different angle and area of the grating has been calculated. Furthermore, the light absorption with different incident angle has been calculated. The optimization results show that the absorption of the solar cell with triangular Ag nanograting structure and anti-reflection film is enhanced up to 96% under AM1.5 illumination in the 300–800 nm wavelength range compared with the reference cell. The physical mechanisms of absorption enhancement in different wavelength range have been discussed. Furthermore, the solar cell with the Ag nanograting is much less sensitive to the angle of incident light. These results are promising for the design of amorphous silicon thin film solar cells with enhanced performance.

Er 3+ -doped TeO 2 –PbF 2 glasses with and without Ag nanoparticles (NPs) were prepared using a melt-quenching method. Ag precipitation was subsequently induced by heat treatment. The influence of Ag nanoparticles on the optical properties of Er 3+ -doped glasses was determined using optical absorption and photoluminescence spectroscopy. Upconversion (UC) emission properties were mainly dominated by the structural properties of the glass matrix. Ag + doping and NP formation contributed to the enhancement of the total UC emission intensities. However, the green emission property of the glasses closely depended on the Ag NP size, and transition from quenching to enhancement occurred when the NP size of the Er 3+ –Ag co-doped glasses was increased. This size-dependent effect originated from the trade-off between the absorption and local field enhancement of Ag NPs with respect to the green emission of Er 3+ ions.

A 1-D plasma model coupled with a well-mixed reactor model was used to simulate the effect of discharge power on the growth properties of hydrogenated microcrystalline silicon films deposited by very high-frequency plasma-enhanced chemical vapor deposition in the high-pressure depletion regime. Although incorporation of higher silicon hydride particles may contribute to additional improvements in deposition rate, SiH 3 remains the dominant deposition precursor responsible for film growth. Good agreement is observed between the model and experimental results. As power increases, the concentrations of deposition precursors in the gas phase also increase, resulting in enhanced emission intensities and deposition rates. Decreases in SiH 3 /H decrease the H concentration in the film and increase the crystalline volume fraction. The intensity ratio and grain size observed during X-ray diffraction depend on the relative growth rates of the facets. Growth of the (110) facet is enhanced by increases in power because of the increase of H concentration in plasma.

In this study, we successfully prepared Er 3+ –Yb 3+ co-doped TeO 2 –PbF 2 oxyfluoride tellurite glasses with different Yb 3+ concentrations and characterized their upconversion properties. Intense emission bands at 527, 544, and 657 nm corresponded to the Er 3+ transitions, and the maximum was obtained at an Yb 3+ -to-Er 3+ molar ratio of 3. When this glass was applied at the back of amorphous silicon solar cells in combination with a rear reflector, a 0.45% improvement in efficiency was obtained under co-excitation of AM1.5 and 400 mW 980 nm laser radiation. Maximum external quantum efficiency and luminescence quantum efficiency of 0.27% and 1.35%, respectively, were achieved at 300 mW excitation.

A bionic fish cilia median-low frequency three-dimensional MEMS vector hydrophone is reported in this paper. The piezoresistive reasonable position was obtained through finite element analysis by ANSYS and the structure was formed by MEMS processes including lithography, ion implantation, PECVD and etching, etc. The standing wave barrel results show that the lowest sensitivity of the hydrophone is −200 dB and reach up to −160 dB (in which the voltage amplification factor is 300). It has a good frequency response characteristics in 25 Hz ∼ 1500 Hz band. Directivity tests displayed that the hydrophone has a good “8”-shaped directivity, in which the resolution is not less than 30 dB, and asymmetry of the maximum axial sensitivity value is less than 1.2 dB.

PbF2:Yb3+,Er3+ nanoparticles were synthesized using the hydrothermal method. The upconversion (UC) luminescence properties of products obtained under different Yb3+ doping concentrations and annealing temperatures were then investigated. As the Yb3+ concentration increased, the product structures transformed from a mixed phase to a cubic phase. Their total emission intensities, however, were remarkably low. After annealing, the UC emission of the products was enhanced because of their increased grain size. The maximum emission was obtained with 7% Yb3+. The products were applied in a hydrogenated amorphous silicon solar cell, and an external quantum efficiency of 0.04% was measured under the illumination of a 980 nm laser at 4.8 W/cm2.

The mechanical process of aluminium thin films under uniaxial tensile strain was simulated with molecular dynamics method in a low temperature range from 40 to 250 K. The stress-strain curve and potential energy-strain curve of aluminium thin film under uniaxial tensile deformation were obtained. The variation characteristics of stress-strain curves with temperature are alike at the elastic stage. However, at the plastic stage the stress-strain curves are grouped into three categories (40 K ≤ T < 100 K, 100 K ≤ T < 200 K, 200 K ≤ T ≤ 250 K). From the stress-strain curves, we found the strange temperature dependence of the local maximum stress, maximal potential energy and their corresponding strain: when the temperature is below 100 K, they go down quickly with temperature, and when above 100 K and below 200 K, they descend slowly and do very slowly above 200 K. Therefore, we have identified two critical temperatures for the transition of plastic flow mechanism.

A 1-D plasma model coupled with a well-mixed reactor model was used to simulate the growth properties of hydrogenated microcrystalline silicon film deposited by very high frequency plasma-enhanced chemical vapor deposition from SiH 4 and H 2 gas mixtures. Plasma parameters of the former, such as electron density and electron temperature, were determined and used as input values for the latter, in which concentrations of gas phase species, crystalline orientation, hydrogen content, surface fraction of dangling bonds, and deposition rate were calculated. Simultaneously, a series of in situ optical emission spectroscopy measurements and film depositions were carried out to investigate the correlation between the model and the experiments. Desired agreements between both were achieved.

Horizontal deflection often occurs when a ray propagates in shallow water with an irregular sea bottom, which makes it difficult to determine eigen-ray trajectory and transmission time. A new method for seeking eigen-ray in three dimensions was proposed and sound speed profile (SSP) was inverted in three-dimensional shallow water using the fastest eigen-ray transmission times to form the cost function. In order to satisfy long-time monitoring of SSP, a kind of sonobuoy was developed with the function of DGPS, short wave radio controlling and dada transmission and experiment was implemented in the South China Sea. It is indicated that the sonobuoy has high reliability and stability in rough sea condition. The precision of SSP inversion can be enhanced dramatically by considering horizontal deflections of eigen-ray. In addition, the influence of small mismatch of seabed depth on precision of inversion can be neglected.

In this paper, we have measured the temperature depended growth properties of hydrogenated microcrystalline silicon (μc-Si:H) films, prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) from SiH4 and H2 gas mixtures. And, a 1D plasma model coupled with a well-mixed reactor model is used to simulate the growth process, in which concentrations of gas phase species, the crystalline orientation, the hydrogen content and the deposition rate are calculated. It suggests that the increasing surface fraction of the dangling bonds with the increase of substrate temperatures is responsible for the increase in the grain sizes. At the same time, the observed variations of the X-ray-diffraction intensities and the deposition rates of the films with temperature result from the differences in the growth rates of the facets.

The upconversion (UC) properties of β-NaYF4:Yb3+(10%),Er3+(1%) microprisms synthesized using a hydrothermal method were studied under different excitation conditions. It was found that the UC emission of β-NaYF4:Yb3+(10%),Er3+(1%) was more sensitive to the 980 nm photons than the 1560 nm photons, because of the high mole ratio of Yb3+/Er3+ in crystals. Applying this material at the back of a hydrogenated amorphous silicon (a-Si:H) solar cell, a short-circuit current density of 64 μA/cm2 was measured under 0.53 W/cm2 980 nm laser excitation. This corresponds to an external quantum efficiency of 0.015% of the solar cell. When co-excited with the 980 nm and 1560 nm lasers, a very weak enhancement in the current was shown, which resulted from the slightly increased red emission. This indicates that co-excitation with multiple wavelengths accessible to the β-NaYF4:Yb3+(10%),Er3+(1%) microprisms is not an effective method to enhance the efficiency of a-Si:H solar cells.

NaYF4:Yb(20%),Er(1%) microcrystals were synthesized using a hydrothermal method, and the effects of the reaction time and the particle size on the up conversion (UC) emission properties were systematically studied. The UC emission intensities of the samples are directly related to the particle size and phase structure. The increase in the reaction time resulted in the phase transformation from cubic nanoparticles to hexagonal microprisms, leading to the enhancement of the UC emission. Moreover, the emission intensities and the intensity ratios of the green and red emissions (Fg/r) of the microprisms, in which a normal two-photon UC process was displayed under excitation with a 980 nm laser, remarkably increased with the increase of grain sizes, resulted from the increase of Yb3+ concentrations in crystals.

β-NaYF 4 :Er 3+ (10%) microprisms, synthesized using a hydrothermal method, were applied to the back of a thin film hydrogenated amorphous silicon (a-Si:H) solar cells to investigate response to sub-band gap near-infrared irradiation. Currents of 0.3 μA and 0.01 μA were measured during single-illumination with 60 mW (80 mW/cm 2 ) 980 nm and 1560 nm diode lasers, respectively, due to frequency upconversion (UC). Under co-excitation by 60 mW 980 nm and 100 mW 1560 nm lasers, a current improvement to 0.54 μA was obtained, resulting from enhancements in red emission. The finding indicates that co-excitation with multiple wavelengths accessible to UC materials is very effective in enhancing the efficiency of solar cells.

Cu2ZnSnS4 (CZTS) films were successfully prepared using a co-electrodeposition-annealing route, in which metal precursor layers were deposited by a co-electrodeposition in aqueous ionic solution, followed by the sulfurization in elemental sulfur vapor ambient at 400 °C for 30 min using nitrogen as the protective gas. The dependence of the structural and optical properties on composition in aqueous solution is investigated. It is shown that CZTS film synthesized at Cu/(Zn + Sn) = 0.71 and Zn/Sn = 1 has a kesterite structure with an absorption coefficient in the order of 104 cm− 1, and the band-gap can be feasible modified by changing the element ratios in solution. This indicates that co-electrodeposition-annealing method is a viable process for the growth of CZTS films for the application in photovoltaic device.

The mechanical process of single-crystal aluminium thin films under uniaxial tensile strain was simulated with molecular dynamics method at different temperature. The stress–strain curve and potential energy–strain curve of thin aluminium film under uniaxial tensile deformation were obtained by molecular dynamics simulations. With the changes of sample temperatures in uniaxial extension, the variation characteristics of stress–strain curves are alike at the elastic stage and different at the plastic one below and above 370 K, respectively. From the stress–strain curves, we gained the first local maximum stress-temperature curve and the strain at the first local maximum stress-temperature curve, and found that the strange temperature dependence of first local maximum stress: when the temperature is above 370 K, the stress goes down quickly with temperature, and when below 370 K, it descends slowly. With increasing temperature, the difference between two strain values corresponding to two maximal potential energies changes slowly below and above 370K but it goes up quickly about 370K. By these dependences, we have identified the critical temperature （370K） for the transition of plastic flow mechanism.

The molecular dynamics simulations are performed with single-crystal copper thin films under uniaxial tensile and cyclic loading to investigate temperature effects on the mechanical responses. With the changes of sample temperatures in uniaxial extension, the variation characteristics of maximum stress, the Young’s modulus, the maximal potential energy, the atomic structure of the emerging dislocation, and activation volume and activation free energy at the maximum stress point make us identify and explain the critical temperature for the transition of deformation mechanism in a temperature range from 293 to 460 K. Under cyclic loading, with raising temperature, the number of cycles to failure of copper films increases under different manners in different temperature range, which can be explained by our constructing model based on the evolutionary features of dislocation. Thus, the mechanisms of the strange temperature dependence of tensile and cyclic deformation have been explained. When the temperature is above 370 K, the rate controlling mechanism is dislocation climbing during uniaxial loading, and the number of cycles to failure goes up quickly with temperature; when below 370 K, the mechanism of uniaxial tensility is mainly characterized by the overcoming of Peierls–Nabarro barrier and a few localized pinnings, the number of cycles rises slowly; and when about 370 K, the mechanism in single-axial tension is pipe diffusion, the number of cycles increases at middle speed.

We present a numerical gas phase reaction model for hydrogenated microcrystalline silicon (μc-Si:H) films from SiH4 and H2 gas mixtures with plasma enhanced chemical vapor deposition (PECVD). Under the typical μc-Si:H deposition conditions, the concentrations of the species in the plasma are calculated and the effects of silane fraction (SF=[SiH4]/[H2+SiH4]) are investigated. The results show that SiH3 is the key precursor for μc-Si:H films growth, and other neutral radicals, such as Si2H5, Si2H4 and SiH2, may play some roles in the film deposition. With the silane fraction increasing, the precursor concentration increases, but H atom concentration decreases rapidly, which results in the lower H/SiH3 ratio.

The molecular dynamics simulations are performed with single-crystal copper thin films under uniaxial tensile loading to investigate temperature effects on the mechanical responses. We found that with increasing sample temperatures, both the maximum stress and the Young’s modulus decrease, but the maximal potential energy increases. So, we identified the critical temperature for the transition of deformation mechanism. Then, the deformation was analyzed by examining the variation of the atomic structure of the emerging dislocation. Finally, activation volume and activation free energy of tensile deformation at the maximum stress point of thin Cu film have been calculated for the first time in a temperature range from 293 to 460 K. Thus, the mechanisms of the strange temperature dependence of tensile deformation have been explained. It is found that there exist three temperature regions, which correspond to different thermal activation mechanisms of dislocation motion. When the temperature is above 370 K, the rate-controlling mechanism is dislocation climbing; when below 370 K, the mechanism is mainly characterized by the overcoming of Peierls–Nabarro barrier and a few localized pinnings; and when about 370 K, the mechanism is pipe diffusion.

Microcrystalline silicon thin film is deposited under different conditions by plasma enhanced chemical vapor deposition. The light stability with different crystallinity and grain size is studied, and the growth mechanism is analyzed using the scaling behavior of roughening surface evolution. Degradation of photoconductivity mainly depends on crystallinity and grain size, but fundamentally, on the growth mechanism. Materials with high crystallinity and large grain size are more stable under light soaking. With the increasing of deposition pressure and input power, growth process transfers to zero diffusion limit growth mechanism, and films deposited present less grain size and poor light stability.