Abstract The intermittency, randomness and fluctuation of low voltage distributed photovoltaic power generation bring problems such as overvoltage, harmonic overlimit and reverse overload to rural distribution network, which seriously affect the power supply quality of low voltage distribution network. This paper mainly analyzes the power quality problems caused by large-scale distributed photovoltaic connected to rural distribution network, such as terminal overvoltage, transformer reverse overload, harmonic overlimit, and three phase unbalance. The power quality management strategy of low voltage station area based on distributed energy storage system is proposed, and the power quality management business module of low voltage station area is built based on the power information acquisition system to verify the reliability of the power quality management strategy of low voltage station area. The application effect of distributed energy storage system in controlling overvoltage, reverse overload and harmonic overlimit in low voltage station is verified through pilot construction.

Objective Wavelength division multiplexing (WDM) in optical fiber communications is widely recognized as the most effective method for increasing communication capacity due to its low cost and ease of implementation. Wavelength division multiplexing and demultiplexer devices (WDMDs) are essential components for implementing WDM technology and have remained at the forefront of optical multiplexing research. Volume Bragg gratings (VBGs) recorded in photo- thermo-refractive glass (PTRG) exhibit extremely narrow spectral bandwidths. These gratings are capable of filter different wavelengths of light by adjusting the incident angle, offering high efficiency, high transmission rates, low insertion loss, and excellent environmental stability. Therefore, they hold great potential for dense wavelength division multiplexing (DWDM) applications. However, the sidelobes caused by sudden changes in coupling strength at both ends of the grating will lead to interchannel interference, preventing the reduction of channel spacing and thereby affecting application performance. In periodic waveguide structures, a method to suppress sidelobes by varying the distribution of coupling strengths is known as apodization. Current research on apodization techniques for VBGs predominantly focuses on using a single function, such as sinc or Gaussian functions, to achieve sidelobe suppression. As far as we know, there has been no systematic comparison of the effects of different apodization functions. Therefore, this study systematically compares and analyzes the results of different types of apodization functions. Methods We build the apodization theoretical model of reflective volume Bragg grating (RVBG) based on F- matrix theory. The diffraction efficiency of different apodized volume Bragg gratings is normalized by defining effective refractive index modulation. The apodization effects of cosine, Gaussian, and secant functions are systematically compared and analyzed. An RVBG filter for the C- band is designed based on the established model, providing a theoretical design basis for the development of high signal-to-noise ratio RVBG filters. Results and Discussions The performance of three refractive index modulation distribution functions, namely cosine, Gaussian, and hyperbolic secant, is examined in RVBGs with a center wavelength of 1550 nm and a thickness of 5 mm. The simulations are conducted to evaluate the efficacy of sidelobe suppression in both the spectral and angular domains. The cosine function exhibits exceptional utilization efficiency in PRRG, with the best diffraction efficiency without additional peaks at the edges of the spectrum for samples of the same thickness and exposure. Gaussian and hyperbolic secant functions demonstrate deeper out- of- band suppression capabilities through parameter adjustments unattainable by the cosine function. However, the hyperbolic secant function exhibits subpar sidelobe suppression, leading to decreased efficiency in utilizing the same glass substrate. The diffraction efficiency of the main lobe in RVBGs is determined by the effective refractive index modulation (ERIM). When the ERIM remains constant, increasing thickness (or refractive index modulation) affects the bandwidth without changing the diffraction efficiency magnitude or spectral shape. Conversely, keeping the thickness constant but changing the maximum refractive index modulation affects both the diffraction efficiency and the spectral features. By adjusting the refractive index modulation and thickness according to requirements, controlling the magnitude of ERIM, and ensuring that the center of the apodization function deviates minimally from the center of the sample, RVBGs with the required performance can be designed and prepared. In addition, Gaussian and hyperbolic secant apodized gratings generate additional peaks at the first zero point, which change periodically with the increase of ERIM. When ERIM is appropriate, these additional peaks disappear. Conclusions Based on F- matrix theory, a theoretical model to analyze the apodized RVBG of various function types is established. By defining the ERIM, normalization of the refractive index modulation for the apodization function is achieved, facilitating easier comparison of results from various apodization functions. We further analyze the apodization influences of cosine, Gaussian, and hyperbolic secant functions. Simulation results demonstrate that apodized gratings significantly suppress sidelobes. With constant diffraction efficiency, all three functions reduce the first and second sidelobes to below 1.1 degrees o and 0.3 degrees o, respectively. The study concludes that the main lobe diffraction efficiency and the shape of the diffraction efficiency spectrum are determined by the ERIM. When the ERIM is fixed, the diffraction efficiency remains consistent, while the spectral bandwidth expands as the grating thickness increases. With a constant thickness, both the diffraction efficiency and bandwidth increase with the maximum refractive index modulation. The capability to reduce the intensity of the first- order sidelobes decreases gradually from cosine to Gaussian to hyperbolic secant functions. An RVBG filter is designed to have a high signal-to-noise ratio based on theoretical research. Utilizing a Gaussian function (m=3) as the apodization function, it achieves an efficiency exceeding 90 degrees o and a spectral bandwidth of less than 0.8 nm. This design allows for the continuous wavelength selection for C- band filters by adjusting the angle, resulting in a sideband suppression of around 50 dB.

The effect of the morphological characteristics of N,N'-dicyclohexylterephthalamide (DCHT), an aromatic bisamide beta-nucleating agent (beta-NA) showing a dual nucleation capability for the beta- and alpha-crystals of isotactic polypropylene (iPP), on the polymorphic composition of iPP and the underlying mechanism were systematically investigated. DCHT crystals differing in their size and distribution state in the iPP melt and recrystallized morphology were obtained by modulating the final heating temperature (T-f), subsequent cooling rate (V-c), and content of DCHT. The crystalline structures formed on the different surfaces of needle-like DCHT crystals were clearly identified. For the iPP/0.1 wt % DCHT samples, the relative fraction of beta-crystal (K-beta value) in the iPP sample nucleated with small-sized needle-like DCHT crystals is much higher than that in the iPP sample nucleated with large-sized needle-like DCHT crystals. This increase is primarily because there is less space for the crystallization of the iPP melt into alpha-spherulites arising from a more homogeneous distribution of small DCHT crystals in the iPP matrix. Upon cooling at the same V-c, dendritic DCHT crystals tend to induce more beta-crystals than needle-like ones, especially at a high V-c, which is predominantly due to an increase in the relative density of beta-nuclei to a-nuclei (N beta/N alpha). Interestingly, it was found that DCHT crystals crystallize into microcrystalline agglomerates in the subsequent cooling process when completely dissolved in the iPP/0.05 wt % DCHT melt. More interestingly, the K-beta value in the iPP sample reaches as high as similar to 1.0 during isothermal crystallization at 135 degrees C, indicating that DCHT microcrystalline agglomerates unexpectedly exhibit a specific nucleation selectivity for beta-crystal. The present investigation elucidates the significant impact of the morphological characteristics of DCHT on the polymorphic composition of iPP, providing a promising way to tune the microstructure and macroscopic performance of iPP materials.

Etch pits formed on (100)-oriented InAs surface by HCl-H2SO4-H2O solutions have been investigated by optical microscopy and atomic force microscopy (AFM) images. Depending on the composition of etchant, four types of etch pits are observed, which is attributed to different reaction rate of (1 1 1)A and (1 1 1)B planes by HCl and H2SO4. Excessive HCl results in long hexagonal shaped pits, whereas the addition of H2SO4 results in tetragonal pits. The direction of the composed pit sidewalls has been determined combining with the results of depth profiles on (110) and (1 (1) over bar0) planes. The role of the HCl and H2SO4 in the over-all etching behavior of InAs and details about the geometrical relation between the sidewalls of the etch pits are discussed.

InAs single crystals grown by the liquid-encapsulated Czochralski (LEC) method and vertical gradient freezing (VGF) are studied by low-temperature photoluminescence spectroscopy, infrared transmission and reflectance spectroscopy, double-crystal x-ray diffraction and Hall effect measurement, respectively. A properly controlled etching solution is used to reveal beautiful square dislocation etch pits in the crystals. In addition to extremely low dislocation density, the concentration of native defects in the VGF-InAs single crystals is much lower than that in LEC-InAs, giving VGF-InAs better electrical and optical properties. The nature of the defects in InAs single crystals is discussed by considering the variation in stoichiometry and environment during the crystal growth processes.

Carbon-ion-implanted InAs was investigated using double-crystal x-ray diffraction (DCXRD), Hall measurement and infrared absorption (IR) analysis. Multiple implantation were made at 0.1–0.4 MeV with 6.0 × 1012–2.0 × 1013 ions cm−2. After rapid thermal annealing at 300 °C for 20 s, the implantation-induced damage was removed substantially, indicating the recovery of crystallinity. The results of Hall measurement reveal strong electrical compensation and low conductivity in the implanted layer of the sample, suggesting the formation of acceptor CAs. In contrast, the lowest IR transmittance is observed in the 300 °C annealed sample, implying the existence of acceptor with significant concentration. The implanted layer turned to n-type after annealing at 400 °C with the increasing transmittance. After annealing at temperature of 500 °C, the decreasing carrier concentration and the increasing transmittance is attributed to the competition between the decomposition of C–H complexes and the formation of donor centers C–C.

Lightly Te-doped GaSb samples grown by the liquid encapsulated Czochralski (LEC) method have been studied by Hall measurements and low-temperature PL spectroscopy. The results suggest that acceptor-related antisite is the dominant defect in n-type GaSb with low Te-doping concentration. As the Te concentration increases, gallium vacancy related defects become the main acceptor. A new band of around 665 meV is observed in the GaSb sample with the lowest Te-doping concentration. The variation of the acceptor defects and their influence on the electronic and optical property on the n-GaSb single crystal are discussed based on the results.

In this work, we report the results of InAs single crystals grown by vertical temperature gradient freezing method (VGF) which has low temperature gradient during the growth process. InAs single crystals with (1 0 0) and (1 1 1) orientation, diameter up to 4 in. have been grown by VGF. Twin-free single crystal ingots with length around 150-200mm have been obtained reproducibly. Etch pit dislocation density (EPD) of the VGF-InAs single crystals is 1000-3000 cm(-2). As-expected, X-ray rocking curve of the VGF-InAs single crystal exhibits a narrower FWHM than LEC-InAs single crystal, indicating a better lattice perfection. In contrast, undoped n type VGF-InAs single crystal has a better electrical property, such as higher electron mobility, lower free electron concentration.

N-type InAs single crystals have been studied by local vibrational mode (LVM) spectroscopy, photoluminescence spectroscopy (PL), glow discharge mass spectrometry (GDMS) and Hall effect measurement, respectively. Carbon–hydrogen complex defects CH3 and CH2 are detected in as-grown and annealed samples. After annealing, CH3 dissociates and more CH2 is formed. Results of PL and Hall measurement suggest that the complex defects of CH3 act as acceptors in n-type InAs and correlate with the change of electrical compensation after annealing. The 383 meV PL peak is attributed to CH3 defects. Based on the expected energy level of CH3 in InAs, we predicted that CH3 complex defects in InAs should introduce a resonant level 32 meV above the valence band minimum.

The electrical transport properties of Mn doped InAs single crystal (InAs:Mn) were determined from temperature-dependent Hall effect measurements over the temperature range of 77-300 K. Both samples were found to be p-type attributed to Mn acceptors randomly substituting for indium lattice sites. The sample with relatively higher doping concentration exhibits characteristics with nearest-neighbor hopping conductance (NNH) in impurity band below 200 K. The ionization energy of the Mn acceptor in InAs is determined to be 27 meV from the analysis of PL spectrum of the lightly doped sample. It is determined from the value of ionization energy that the localized radius a(0) of the manganese acceptor is 17 angstrom.

p型单晶硅太阳电池在EL检测过程中,部分电池片出现黑斑现象.结合X射线能谱分析(EDS),对黑斑片与正常片进行对比分析,发现黑斑片电池与正常电池片大部分表面的成分相同,排除了镀膜及丝网印刷过程中产生黑斑的可能.利用X射线荧光光谱分析(XRF)测试了同一电池片的黑斑区域与正常区域,发现黑斑处Ca含量较大,并出现Sr、Ge和S等杂质元素.将6个档位的电池片制备成2 cm×2 cm的电池样片,利用光生诱导电流测量了每个电池的外量子效率(EQE).在460～1 000 nm波长范围内,同一电池片黑斑处与正常处的EQE相差较大,说明黑斑的出现与原生硅片缺陷无关,应归结于电池片生产过程中引入的杂质缺陷.给出了杂质引入的原因以及解决途径,从而显著减小了黑斑片产生的几率.

Undoped, S-doped and Fe-doped 4 inch diameter (100) InP single crystals with average dislocation etch pit density less than 5000 cm-2 have been grown by using high pressure vertical temperature gradient Freeze (VGF) method.A multiple points X-ray double crystal diffraction measurement across the 4 inch wafer indicates a full width at half maximum (FWHM) around 30 arcsec with uniform distribution of the rocking curves.Due to the low temperature gradient during the VGF growth process, the possibility of twin generation is quite high compared to that of liquid encapsulated growth process (LEC).However, the orientation of the crystal main body is still (100) direction after the twin formation on the VGF-InP crystal ingots.In this case, a large quantity of (100) single crystal wafers with diameter of 2 inch, 3 inch and 4 inch can be sliced from the ingot.Since the effective segregation coefficient is very low for Fe, polycrystal growth caused by composition super cooling of Fe-doped InP VGF is found frequently.The single crystal yield of the Fe-InP VGF growth can be increased significantly by strictly control the Fe doping quantity and the temperature gradient.Electrical property, dislocation density and its distribution, lattice perfection of the VGF-InP single crystals have been investigated.

SiN x /SiO x passivation and double side P-diffusion gettering treatment have been used for the fabrication of c-Si solar cells. The solar cells fabricated have high open circuit voltage and short circuit current after the double P-diffusion treatment. In addition to better surface passivation effect, SiN x /SiO x layer has lower reflectivity in long wavelength range than conventional SiN x film. As a consequence, such solar cells exhibit higher conversion efficiency and better internal quantum efficiency, compared with conventional c-Si solar cells.

Undoped and Te-doped 4 inch diameter (100) GaSb single crystals in 5-8 kg weight have been grown by using liquid encapsulated Czochralski (LEC) and substrate wafer have been prepared.By optimizing the thermal field, single crystal yield as high as 80% have been achieved.Dislocation etch pit density (EPD) of the wafer is less than 500 cm-2 and its X-ray diffraction rocking curves has a full width at half maximum (FWHM) around 29 arcse, indicating a high lattice perfection.The wafer has good electrical uniformity, benefiting from the flat solid-liquid interface during the single crystal growth process.Epi-ready 4 inch GaSb substrate wafer with good flatness and low surface roughness has been prepared.N type GaSb wafer with good near infrared transmittance has been prepared by controlling the native acceptor concentration and doping concentration.

GaSb is the most suitable substrate in the epitaxial growth of mixed semiconductors of GaSb system.In this work,Te-doped GaSb bulk crystals with different doping concentration have been annealed at 550℃ for100 h in ambient antimony.The annealed samples have been studied by Hall effect measurement,infrared(IR)optical transmission,Glow discharge mass spectroscopy(GDMS) and photoluminescence(PL) spectroscopy.After annealing,Te-doped GaSb samples exhibit a decrease of carrier concentration and increase of mobility,along with an improvement of below gap IR transmission.Native acceptor related electrical compensation analysis suggests a formation of donor defect with deeper energy level.The mechanism of the variation of the defect and its influence on the material properties are discussed.

Te-doped GaSb single crystals are studied by measuring Hall effect, infrared (IR) transmission and photoluminescence (PL) spectra. It is found that the n-type GaSb with IR transmittance can be obtained as high as 60% by the critical control of the Te-doping concentration and electrical compensation. The concentration of the native acceptor-associated defects is apparently low in the Te-doped GaSb compared with those in undoped and heavily Te-doped GaSb. The mechanism for the high IR transmittance is analyzed by considering the defect-involved optical absorption process.

As-grown and annealed undoped n type InAs single crystals have been studied by Hall effect measurement, infrared transmission (IR) spectroscopy, photoluminescence spectroscopy (PL) and glow discharge mass spectroscopy (GDMS). After annealing, below-gap infrared transmittance of the InAs single crystal increases significantly with the annihilation of a 0.383 eV PL peak related defect. Mechanism of the transmission enhancement and the attribution of the defect is discussed based on the experimental results.

Undoped p-type Ga Sb single crystals were annealed at 550–600?C for 100 h in ambient antimony. The annealed Ga Sb samples were investigated by Hall effect measurement, glow discharge mass spectroscopy（GDMS）, infrared（IR）optical transmission and photoluminescence（PL） spectroscopy. Compared with the as-grown Ga Sb single crystal, the annealed Ga Sb samples have lower hole concentrations and weak native acceptor related PL peaks, indicating the reduction of the concentration of gallium antisite related native acceptor defects. Consequently, the below gap infrared transmission of the Ga Sb samples is enhanced after the thermal treatment. The mechanism about the reduction of the native defect concentration and its influence on the material property were discussed.

人类发展离不开能源的开发利用，但目前矿石能源的消耗对自然环境的破坏已经严重影响，太阳能被认为是未来清洁能源的主要供给方式，这也是近几年光伏产业得以飞速发展的主要原因。目前光伏发电成本较高，不能实现自身健康的商业化发展模式。支撑目前光伏产业发展的技术路线包括以下几个环节：硅提纯，定向凝固制备单晶棒或多晶锭，线切，电池片及组件生产，电站建设。但是光伏产业下游产品的附加值远低于半导体行业下游产品（如集成电路等）的附加值，导致光伏产业上游较高的生产加工成本占光伏发电总成本比例较高。因此，必须找到一条适合光伏产业发展的、低成本、环境友好的技术路线。

Low dislocation density Ge wafers grown by a vertical gradient freeze (VGF) method used for the fabrication of multi-junction photovoltaic cells (MJC) have been studied by a whole wafer scale measurement of the lattice parameter, X-ray rocking curves, etch pit density (EPD), impurities concentration, minority carrier lifetime and residual stress. Impurity content in the VGF-Ge wafers, including that of B, is quite low although B2O3 encapsulation is used in the growth process. An obvious difference exists across the whole wafer regarding the distribution of etch pit density, lattice parameter, full width at half maximum (FWHM) of the X-ray rocking curve and residual stress measured by Raman spectra. These are in contrast to a reference Ge substrate wafer grown by the Cz method. The influence of the VGF-Ge substrate on the performance of the MJC is analyzed and evaluated by a comparison of the statistical results of cell parameters.