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The energy extracted from solar radiation is the most abundant and accessible source of renewable energy, which will become progressively more important as time goes on. Solar cells are regarded as one of the most promising candidates for generating renewable clean energy. Recently, a new class of semiconducting material called organic-inorganic halide perovskite has received great attention of academia, and the record power conversion efficiency (PCE) of perovskite solar cell (PSC) rapidly increased from 3.8% in 2009 to 22.7% in late 2017 through intensive research due to some advantages as follows. 1) Excellent optoelectronic property. Perovskite materials exhibit excellent properties, including long diffusion length, high carrier mobility, and high absorption coefficient. 2) Low cost. The ingredients of perovskite materials are cheap, and PSCs can be manufactured by a solution process. 3) Tunable bandgap. Perovskite materials have highly tunable bandgap (1.2-2.2 eV), contributing to the further improvement in PCE of single junction PSCs by realizing the ideal bandgap (1.3-1.4 eV) as demonstrated by the Shockley-Queisser detailed balanced calculation. The basic architectures of PSCs are divided mainly into mesoscopic and planar heterojunction structures. Compared with the former configuration, the later configuration combined with low-temperature processable interlayers provides a method of fabricating flexible PSCs and tandem PSCs. Furthermore, the nonuse of the mesoscopic structure simplifies the structure of PSCs and reduces the cost and time of fabrication. The key requirement to achieve an efficient and reproducible planar heterojunction PSCs is that the perovskite layer should be uniform, continuous, and pinhole free to minimize shunting pathways. So, significant research effort is being devoted to the quality management of perovskite films with the goal of achieving the controllable preparation, including the optimization of their morphology (uniformity, coverage, roughness) and microstructure (grain size/distribution, texture), and the elimination of defects (voids, pinholes, grain boundaries), which influence the PSC performance directly. Especially for the one-step solution coating method, the film quality of perovskite on different planar substrates under varied deposition conditions exhibits a large difference, due to the complex crystallization process and the heightened sensitivity to environmental conditions. In this paper, the characteristics of perovskite materials, the nucleation-growth mechanism of films in the one-step solution method, and the evolution of cell structures are described briefly. The latest quality control methods of high-quality perovskite films prepared by solution method are then discussed emphatically. Finally, to provide references for the future research, the development and existing problems of PSCs are addressed and prospected.

In the real ocean environment, the compressional and shear wave velocities in an elastic sediment layer vary with depth, leading to the coupling between compressional and shear waves. As the coupling will affect the underwater sound field, in this paper, a typical sound velocity distribution (where the compression wave velocity has an n2 linear distribution and the square of shear wave velocity has a linear distribution) is analyzed. Based on the wave equation in inhomogeneous elastic medium, coupled equations of wavenumber kernels of scalar and vector potential functions are established. Based on the perturbation method, approximate analytical solutions of integration kernels are acquired by successive differentiation. The comparison between theoretical prediction and experimental data, which are from the pressure sensor of ocean-bottom seismometer (OBS) consisting of three orthogonal hydrophones and one hydrophone, located at the bottom of the sea near Qingdao City, shows that the coupling between shear wave and compression wave has little effect on near-field sound propagation, while the prediction of long-range sound propagation needs to consider the influence of eigenvalue change caused by coupling. Theoretic analysis shows that there will be coupling between the two waves only if the gradient, σ, of the square of the shear wave velocity is nonzero. When α, the gradient of the reciprocal of the square of the compression wave velocity, becomes larger, and σ remains unchanged, the simulation results show that the change of the eigenvalue is very small when considering the coupling effect. Thus, transmission loss curves calculated by the coupled and uncoupled algorithm are almost the same. When σ becomes larger while α remains unchanged, the simulation results show that eigenvalues are changed to some extent if considering the coupling effect, and that the difference between transmission loss calculated by the coupled and uncoupled algorithms increases. That means the effect of σ value on coupling is greater than that of α value. In addition, the coupling between the compression wave and shear wave can lead the eigenfunctions and derivative eigenfunctions in the sediment to change. The horizontal displacement and vertical displacement are the Fourier-Bessel integral functions of eigenfunctions and derivative eigenfunctions. So the displacement field of particle in the sediment layer is different in the coupled case from that in the uncoupled cases. By comparing the transmission loss of sound pressure simulated by COMSOL software and that obtained from our proposed method, the correctness of the proposed method is verified. And the calculation time is much shorter than the calculation time by using COMSOL software.

Inorganic-organic metal halide perovskite solar cells (PSCs) have drawn tremendous attention as a promising next-generation solar-cell technology because of their high efficiencies and low production cost. Since the first report in 2009, the recorded power conversion efficiency (PCE) of PSCs has rapidly risen to 22.1% by using 2, 2', 7, 7'-tetrakis (N,Ndi-p-methoxyphenyl-amine) 9,9-spirobifluorene (spiro-MeoTAD) as hole transport material (HTM), with the efforts devoted to the device architecture optimization, material compositional engineer and interface engineering. Nevertheless, the synthesis and cost of the organic HTM (OHTM) become a major challenging issue and therefore alternative materials are required. In the past few years, the applications of inorganic HTMs (IHTMs) in PSCs have shown large improvement in PCE and stability. For example, PSCs with CuOx as IHTM reached a PCE of 19.0% with better stability. Even more exciting, the theoretical PCE of PSC based on Cu2O HTM reaches 24.4%. So, Cu2O is a promising IHTM for future optimized PSC and the large area uniform preparation is very important. In this paper, Cu2O films have been successfully prepared using electron beam evaporation followed by air annealing. The influences of annealing temperature and time on the composition, structure, and photoelectric characteristics of film are investigated in detail. It is found that the as-deposited film is a mixture of Cu2O and Cu. With the increase of annealing temperature, material composition is transformed from mixture to pure Cu2O phase, and then to CuO, due to the oxidation in air. In an annealing temperature between 100℃ to 150℃, pure Cu2O film can be obtained with an average transmission rate over 70%, optical band-gap of 2.5 eV, HOMO level of -5.32 eV, and a carrier mobility of 30 cm2·V-1·s-1. When the film is treated with a UV lamp, the structure and composition of the film can be changed more easily because of the enhancement of oxidation. Finally, reverted planar PSCs with the structure of Ag/PCBM/CH3NH3PbI3/HTMs/ITO are constructed and compared carefully based on HTMs of Cu2O, with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS), and Cu2O/PEDOT:PSS layers, respectively. An optimum thickness of 40 nm of Cu2O HTM is achieved with high carrier extraction rate. However, the performances of all of the PSCs are inferior to those of PEDOT:PSS-based devices, due to the formation of pinholesin absorber layer resulting from the strong hydrophobicity of Cu2O film. However, the efficiency of PSC based on Cu2O/PEDOT:PSS double-HTM is deteriorated because of the chemical interaction between PEDOT:PSS and Cu2O. These findings provide some important guidelines for the design of HTMs.

With the advances of ship noise reduction technology, the working frequency of the passive sonar must be reduced in order to detect a target. For the conventional array, it requires a large array aperture, comparable to the wavelength, in order to achieve an acceptable angular resolution. Arrays of small physical size with high angular resolution are thus attractive for low-frequency direction-of-arrival estimation of underwater sound source. In this paper, we consider a 33 uniform rectangular array which consists of vector sensors with inter-sensor spacing much smaller than the wavelength. A broadband super-directive beamforming method is proposed for this vector sensor array, which extracts multi-pole modes of different orders from the spatial differentials of the sound field. By normalizing the amplitudes of the multi-pole modes, frequency invariant mode functions can be obtained, which are used to build the desired beam pattern, despite the Rayleigh limit on the achievable angular resolution. Vector sensors are used to replace the pressure difference operation, thus to achieve a desirable beam pattern, the order of spatial differential will be reduced. In other words, for the same array configuration, using the vector sensors provides higher directivity than using the pressure sensor. To concentrate on the sources, and to minimize all hindrances from around circumference, a suitable beam pattern is constructed as an example to analysis. To verify the algorithm, a prototype is built and tested in a water tank. Comparisons are carried out between the actually synthesized beam patterns and the theoretical ones. The experimental results show good agreement with the theoretical results, and that the directivity increases with the multi-pole mode order increasing, at the expense of lower robustness. The performances for different values of ka are also investigated, where k is the wave number and a denotes the inter-sensor spacing. Simulation results show that when the inter-sensor spacing is no more than one-sixth of the incident wave length, the error introduced by the approximations for muti-pole mode extraction can be neglected. It should be noted that this result of the inter-sensor spacing still applicable when considering array gain, showing that the array is insensitive to uncorrelated noise while preserving a relatively high array gain. Finally, the influence of the underwater acoustic waveguide on the array performance is analyzed. Simulations and experimental tests show that due to the small array aperture, the waveguide effects on the array performance are limited.

Metal nanoparticles with low cost and high performance have good potential applications in light-trapping of solar cells. In this paper, a three-dimensional model is proposed to simulate the light absorption of microcrystalline silicon (μc-Si:H) thin film solar cells. The effects of spherical and hemispherical Al nanoparticle arrays located on the front surfaces of solar cells are investigated, and the particle radius and array period are optimized by the finite element method. The results show that the optimal Al nanoparticle arrays can enhance broadband absorption in thin film solar cells. For spherical particle arrays, the key parameter that influences light absorption in solar cells is period/radius ratio (P/R) or particle surface coverage. When P/R=4-5, the optimum integrated absorption enhancement (Eabs) is over 20% under AM1.5 illumination compared with the solar cell without nanoparticles. The value of Eabs is small and decreases with the increase of P/R when P/R>5, and Eabs is less than zero when P/RP=500 nm and R=120 nm, the spectral absorption rate as a function of wavelength shows broadband absorption including four distinct peaks, which are attributed to quadrupole plasmon resonance mode, dipole resonance mode and waveguide mode respectively according to the electric field distribution in the solar cell. For hemispherical particle arrays, the maximum value of Eabs is 24.5%, which is higher than that of the solar cell with optimized spherical particle arrays. This is due to the high coupling efficiencies of the particles, so that most of the scattered light is directly coupled into the substrate. However, the value of Eabs is very sensitive to the hemispherical particle radius. As the radius decreases, the scattering cross-section and scattering efficiency of the particle decrease dramatically. As the radius increases, the dipole plasmon resonance wavelength rapidly shifts towards longer wavelength (red shift). Both of these are detrimental to absorption enhancement of solar cells. Thus we conclude that spherical Al particle arrays are more preferable in actually fabricating the light-trapping of solar cells.

The intrinsic silicon thin film for passivation of the crystalline silicon wafer surfaces in silicon heterojunction cells was prepared by very high fregucency plasma enhanced CVD (VHF-PECVD). Plasma emission versus time was recorded by optical emission spectroscopy (OES) during the silicon thin film deposition. Results show that the Hα* and SiH* signals stabilize soon (about 25 s after deposition) under the optimized deposition conditions, and the variation of SiH*/Hα* ratio is little, thus avoiding the structure non-uniformity of silicon film during the growth. The reason is that the SiH4 back diffusion is avoided owing to SiH4 being not fully depleted. The study of the influence of the deposition parameters on steady-state plasma emission spectra and properties of silicon films shows that as the SiH4 concentration increases, the Hα* decreases and the SiH* increases, the silicon film will transit from microcrystalline to amorphous, and the good passivation effect can be achieved in the amorphous silicon film. Hα* and SiH* increase firstly and then decrease with the deposition pressure, the decrease of Hα* and SiH* under high pressure can be attributed to a high polymer formation which is not beneficial to the formation of high quality silicon film, and therefore the passivation effect of silicon films decreases under high pressures. Hα* and SiH* increase with power density, and are saturated when the power density is 150 mW/cm2; for this the quality and passivation effect of the silicon film begin to decrease, the passivation effect of the silicon film at a power density of 50 mW/cm2 is poor, which may be due to the low concentration of atomic H being unable to fully passivate the dangling bonds at the silicon surface.

Bi-static long-range bottom reverberation in shallow water is investigated, and the impulse response function is derived using the linear theory of sound channel. For the case of almost layered medium, the adiabatic mode solution is introduced for the derivation of transfer function. The reverberation intensity is calculated for the range-dependent waveguide, and then both the intensities and the decaying rules are compared with their corresponding counterparts in different wedged sea areas. It is shown that the propagation effect on intensity of distant bottom reverberation can not be neglected for the bi-static active sonar in shallow water waveguide.

In the high rate deposition of device grade microcrystalline silicon films and their solar cells, plasma enhanced chemical vapor deposition excited using very high frequency (VHF) has become a mainstream method. Although, great breakthroughs in the experiment are achieved, the depositional mechanism is still a research hot spot and difficulty point. In this paper, the capacitively-coupled hydrogen plasma discharge at VHF is simulated. A two-dimensional, time-dependent axial symmetry model is adopted at a frequency of 75 MHz, and the influences of pressure and plasma power on hydrogen plasma characteristic are simulated. At the same time, the hydrogen plasma is monitored on-line using the optical emission spectrometry in experiment. The results show that the value of the electronic concentration ne takes a maximum in the middle of the plasma bulk, while the electron temperature Te and the number densities of Hα and Hβ each have a maximal value at the place near the sheath and plasma bulk; the potential decreases with pressure increasing from 1 Torr to 5 Torr, the electron concentration in the plasma bulk first increases with the increase of pressure, then decreases with the further increase of pressure, but the electron temperature first decreases and then keeps stable in plasma bulk; the electron concentrations, Hα and Hβ increase linely with power increasing from 30 W to 70 W, but the electron temperature keeps stable. The experimental results and simulation results are in good agreement.

Three sets of hydrogenated microcrystalline silicon （μc-Si:H） films for different deposition time were prepared by very high frequency-plasma enhanced chemical vapor deposition with different deposition rates. The surface roughness evolution of μc-Si:H has been investigated using spectroscopic ellipsometry. For films with the deposition rate of 0.08 nm/s and 0.24 nm/s, the surface roughness of films changes a little, and the growth exponent β is about 0.20. Similar β values ascribed to the adatoms have enough time to move to the site with lower energy under lower deposition rate. However, when the deposition rate increases to 0.66 nm/s, the surface roughness of films increases obviously, and the exponent β is about 0.81, which is much higher than 0.5 for zero diffusion limit in the scaling theory. The growth mode of high-rate deposited μc-Si:H is clearly different from that of lower-rate deposited μc-Si:H. This is due to the fact that the adatoms have no enough time to diffuse before being covered by the radicals of the next layer under high deposition rate, which decreases the surface diffusion of the adatom, and therefore increases the film surface roughening which results in a larger β. The case of β>0.5 is related to the shadowing effect.

The scaling behaviour of surface roughness evolution of high rate deposited μc-Si:H by very high frequency plasma-enhanced chemical vapor deposition （VHF-PECVD） is investigated using spectroscopic ellipsometry （SE）. Films deposited at Pg=300 Pa with deposition rate of 5 ?/s, show abnormal scaling behavior with the exponent β of about 0.81, which is much larger than 0.5 of zero diffusion limit in the scaling theory. This implies that there are some roughening increasing mechanisms, and this roughening increasing mechanism is correlated with the shadowing effect.

P-type hydrogenated microcrystalline silicon thin films have been prepared by radio-frequency plasma-enhanced chemical vapor deposition with B2H6 as a doping gas. The effects of substrate temperature and the doping ratio on the microstructure and dark conductivity of the p-type hydrogenated microcrystalline silicon films have been investigated. The results show that the films deposited at higher substrate temperature are amorphous even if the doping ratio is very low. The crystalline volume fraction of films monotonically decreases and the dark conductivity initially increases slowly and then decreases rapidly with substrate temperature increasing, which is very similar to the effects of the doping ratio. Finally the growth mechanism of p-type hydrogenated microcrystalline silicon thin films has been discussed in particular.

Undoped hydrogenated silicon films have been prepared from a gas mixture of silane and hydrogen, at deposition temperature varying from 200—450℃ in an ultrahigh vacuum system using RFPECVD technique. Raman scattering, SEM and UV spectrophotometer are used to analyse the structure changes of microcrystalline silicon films throughout the deposition temperature range. Results show that at lower deposition temperature, the crystalline volume fraction of μc-Si:H films increased with the increasing of deposition temperature. Exceeding a certain temperature, the crystalline volume fraction decreased with further increasing of deposition temperature. This is attributed to a change in the dominant film growth process from surface-diffusion-limited at low deposition temperatures to flux-limited at higher deposition temperatures.

Using high-deposition-pressure technique, high-quality microcrystalline silicon film was prepared by radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) combined with rapid thermal treatment. The volume fractions of the amorphous and microcrystalline phases and optical properties of microcrystalline silicon were carefully studied by Raman spectra, reflectance spectra and transmittance spectra. The results show a red shift of the absorption edge of microcrystalline silicon, which can be due to the increase in the volume fractions of the amorphous and microcrystalline phase and decrease in the band tail states.

Diamond thin films of different structures were prepared by using chemical vapor deposition on WC(6%Co) substrates under different conditions.Reman spectroscopy was used for the quality evaluation of the diamond films.The cracking size in indentation tests was used for the evaluation of adhesion strength,and the influence of structure of diamond films on the adhesion was studied.Results obtained show that: (1) The buffer role of sp2_carbon between grain boundaries greatly affect the residual stress of the film,hence the cracking size decreases steadily with increasing sp2 content.(2) The increase of nucleation density is mainlyh due to the contribution of the diamond seed grains left. In this case,the increase of nucleation density cannot effectively improve the chemical adhesioe force between the film and the WC substrate,and cannot improve the adhesion between the film and the substrate.(3)For thinner films there is no compressive stress among diamond grains,hence the cracking size does n t increase apparently with increasing deposition time.Strong compressive stress emerges only after the thickness increases to a certain value,and then the cracking size increases rapidly with increasing deposition time.

CNx films were prepared by using microwave plasma-enhanced chemical vapor phase deposition. As-deposited films were analyzed by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy and Raman spectroscopy. Field electron emission characteristics of thin films were studied. Experimental results indicate that the film structure and properties of the field electron emission are related to flow ratio of N2 to H2 while the flow rate of CH4 was kept at 8 sccm. When the flow ratio of N2 to H2 was 50/50 sccm, the obtained film had a nano-crystalline graphitic structure with curved basal planes (fullerene-like structure) and excellent properties of field electron emission. The turn-on field decreased to 1.1 V/μm. At an electric field of 5.9V/μm, the average current density was 70μA/cm2 and emission sites density was larger than 1×104cm-2.

Diamond thin films were prepared by using chemical vapor deposition. It is enhanced to etch the sp2 bonding carbon atoms of the film by intermittently closing the methane gas during the deposition. These films were characterized by Raman spectroscopy and microscopy. The results show that the enhanced etching of sp2 bonding carbon atoms has no obvious effect on quality and microstructure of the diamond films. It reveals that the sp2 bonding carbon atoms do not mainly exist in graphitic or amorphous carbon grain form in the films but mainly among the carbon atoms of diamond grain surface or grain boundary.

We present results of a theoretical calculation of the electronic structure of the two polar ZnSe/GaAs(100) interfaces. The bulk electronic structure is described by the nearest neighbor tight binding formalism. Using the scattering theoretical method, we have obtained wave vector-resolved interface layer densities of states and the interface band structure. For both Se/Ga and As/Zn interfaces, there exist no interface states in the fundamental gap, but there are three interface bands and four semi-resonance bands in the valence-band region. Finally, we study the nature and origins of these bands by analysing orbital-resolved layer densities of states.