Y2O3:Bi,Yb减反转光薄膜的制备及其性能研究

采用脉冲激光沉积(PLD)方法在湿法腐蚀后的Si(100)衬底上制备了Y₂O₃:Bi,Yb减反转光薄膜。所制备的薄膜在300~800 nm波长范围内的平均反射率最低至5.28%,同时在晶体硅太阳能电池最佳响应范围内的980 nm附近表现出了良好的下转光特性。与非减反下转光薄膜相比较,具有减反结构的Y₂O₃:Bi,Yb下转换薄膜的转光强度有了明显的提升。随着衬底腐蚀时间在一定范围内的延长,Bi³⁺和Yb³⁺的发射峰强度线性增大。该减反转光薄膜为太阳能电池效率提高提供了一种简单可行的方法。     

Improved performance of silicon‐nanoparticle film‐coated dye‐sensitized solar cells

Silicon (Si) nanoparticles with average size of 13 nm and orange–red luminescence under UV absorption were synthesized using electrochemical etching of silicon wafers. A film of Si nanoparticles with thickness of 0.75 µm to 2.6 µm was coated on the glass (TiO₂ side) of a dye‐sensitized solar cell (DSSC). The cell exhibited nearly 9% enhancement in power conversion efficiency (η) at film thickness of ～2.4 µm under solar irradiation of 100 mW/cm² (AM 1.5) with improved fill factor and short‐circuit current density. This study revealed for the first time that the Si‐nanoparticle film converting UV into visible light and helping in homogeneous irradiation, can be utilized for improving the efficiency of the DSSCs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New issue of GaN nanoparticles solar cell

This study involves the synthesis of gallium nitride (GaN) nanoparticles (NPs) under different low temperatures using a simple chemical method. The nanoparticles are spin coated on Si substrate to fabricate the solar cell. The FESEM images obtained indicate the presence of cubic GaN nanoparticle with average diameter of 50 nm synthesized at 90 °C. The spin coating technique deposited n-GaN NPs/Si(111) produced a heterojunction solar cell with fill factor of 0.56 and conversion efficiency of 2.06%. Based on these results, this study proposes a novel low cost technique for the fabrication of GaN NPs solar cells.     

A new proposal for Si tandem solar cell: Significant efficiency enhancement in 3C–SiC/Si

In order to considerable enhancement of the efficiency of silicon solar cells, in this paper, for the first time, we present a new proposal for silicon based tandem solar cells. For investigation of this idea, we have evaluated the characteristics of 3C–SiC/Si crystalline tandem solar cells connected series by a tunneling junction, under air mass 1.5 global irradiance spectrums. A 2D simulation including the effects of surface passivation, back surface field (BSF), and carrier tunneling have been performed to obtain the optical and electrical characteristics of single junction silicon, 3C–SiC, and finally the tandem cells. The obtained data illustrate that the best design parameters considering the experimental limitations can be obtained. High energy conversion efficiency for the proposed structure of 26.09% has been achieved for 3C–SiC/Si tandem structure driven by 20.49% and 17.86% conversion efficiencies of single junction Si and 3C–SiC solar cells, respectively. Our results justifies that the higher conversion efficiency of the Si-based tandem structure compared with 3C–SiC and Si cells stems from enhancement of open circuit voltage and fill factor parameter at the hands of decrease in short circuit current limited by the top 3C–SiC cell.     

硅BC8量子点太阳能电池中的多重激子效应

多重激子效应是指在纳米半导体晶体中,量子点吸收一个高能光子而产生多个电子-空穴对的过程,该效应可以提高单结太阳电池能量转换效率。利用碰撞电离机制和费米统计模型计算了工作温度300 K的单结硅BC8量子点太阳能电池在AM1.5G太阳光谱下的能量转换效率。对于波长在280~580 nm的入射光,多重激子效应可以大幅增强硅BC8量子点直径d>5.0 nm的量子点太阳电池的能量转换效率。硅纳米量子点的直径d=6.3~6.4 nm时,最大能量转换效率为51.6%。     

Hybrid polymer/inorganic nanoparticle blended ternary solar cells

Hybrid polymer/inorganic nanoparticle blended ternary solar cells are reported. These solar cells have an active layer consisting of PbS colloidal quantum dots (CQDs), poly (3‐hexylthiophene) (P3HT), and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM). Power conversion efficiency (PCE) was improved by incorporating PbS CQDs in the active layer of P3HT:PCBM‐based organic solar cells. As the concentration of PbS CQDs in the hybrid solar cells was increased, PCE was also increased. This improvement resulted from improved charge transfer and also extended light absorption into the near‐infrared. The PCE of the hybrid solar cells was 47% higher than that for reference organic solar cells on average under air mass 1.5 global illumination. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectral downshifting from blue to near infer red region in Ce3+-Nd3+ co-doped YAG phosphor

The YAG phosphors co-doped with Ce³⁺-Nd³⁺ ions by varying concentration of Nd³⁺ ion from 1 mol% to 15 mol% were successfully synthesized by conventional solid state reaction method. The phosphors were characterized by powder X-ray powder diffraction (XRD) and surface morphology was studied by scanning electronic microscope (SEM). The photoluminescence (PL) properties were studied in near infra red (NIR) and ultra violet visible (UV–VIS) region. The synthesized phosphors can convert a blue region photon (453 nm) into photons of NIR region (1063 nm). The energy transfer (ET) process was studied by time decay curve and PL spectra. The theoretical value of energy transfer efficiency (ETE) was calculated from time decay luminescence measurement and the maximum efficiency approached up to 82.23%. Hence this phosphor could be prime candidate as a downshifting (DS) luminescent convertor (phosphor) in front of crystalline silicon solar cell (c-Si) panels to reduce thermalization loss in the solar cells.     

Heterojunctions of TiO2 nanoparticle film and c-Si with different Fermi level positions

The photovoltaic properties of heterojunctions of titanium dioxide (TiO₂) nanoparticle films with single crystal silicon (c-Si) substrates with different Fermi level (E _f) positions were studied. The TiO₂ nanoparticles of rutile and anatase structures were studied without any sintering process. To clarify the photovoltaic properties, the characteristics of the heterojunction solar cells of TiO₂ nanoparticle films with p-Si and n-Si substrates were investigated, where several Si substrates with different resistivities were used. The I–V characteristics of p-Si/TiO₂ heterojunction showed the rectifying behavior and photovoltaic effect. The n-Si/TiO₂ heterojunction also showed good rectifying characteristics; however, the conversion efficiency was extremely lower than that of p-Si/TiO₂ heterojunction. The conversion efficiencies of various Si/TiO₂ (rutile) heterojunction solar cells against the Fermi level E _f of c-Si showed the maximum in the p-doped region. The photovoltaic properties of the Si/TiO₂ heterojunction also depended on the crystal structure of TiO₂, and the conversion efficiency of anatase is higher than that of rutile, which was attributed to the higher carrier mobility of anatase.     

The structure and optical properties of SiC film on Si (111) substrate with a ZnO buffer layer by RF-magnetron sputtering technique

We have fabricated a multiply layer SiC/ZnO on Si substrates using the RF-magnetron sputtering technique with the targets of a single crystalline SiC and a polycrystalline ZnO. The as-deposited films were annealed in the temperature range of 600–1000 °C under nitrogen ambient. We have observed a strong ultraviolet (UV) emission (370 nm) from the as-deposited SiC/ZnO film and an intense violet emission (412 nm) from the film annealed at high temperature (1000 °C) under nitrogen ambient. The SiC film quality and the PL intensities are considered to be strongly dependent on the crystalline quality of the ZnO buffer layer. With the increase of the annealing temperature, the crystalline quality of the ZnO buffer layer is improved, resulting in the improvement of the SiC film quality and the increase of the PL intensities. The thin films have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) to provide the evidences of photoluminescence (PL). We suggest that the UV emission could be attributed to the nanocrystal silicon particles, that the 395 nm band is related to ZnO buffer layer and has a great relation to the crystalline quality of the ZnO film, and that the violet emission is associated with the emission luminescence from 6H-SiC, which bears on the SiC film quality. The obtained results are expected to have important applications in modern optoelectronic devices.     

Fabrication of high growth rate solar-cell-quality μc-Si:H thin films by VHF-PECVD

Several series of Si:H films were fabricated by the very high frequency plasma enhanced chemical vapour deposition (VHF-PECVD) at different substrate temperatures (T_s) and silane concentration (SC=[SiH_4]/[SiH_4+H_2]%). The results of Raman spectroscopy showed structural evolution of the Si:H films with the variation of T_s and SC. The results of x-ray diffraction (XRD) measurements indicated that T_s also influences the crystal orientation of the Si:H films. The modulation effect of T_s on crystalline volume fraction (X_c) is more evident for the high SC, which shows different trend compared to low SC. In addition, the growth rate of the films also showed a regular change with the variation of SC and T_s. Different samples in the series showed a similar increase in dark conductivity and a decrease in photosensitivity with increasing T_s and decreasing SC. Device-quality microcrystalline silicon materials were deposited at a high growth rate, characterized by relatively low dark conductivity and relatively high photosensitivity in a certain crystalline range. The microcrystalline silicon solar cell with a conversion efficiency of 4.55% has been prepared by VHF-PECVD.     

Synthesis and evolution of hollow ZnO microspheres assisted by Zn powder precursor

Hollow ZnO microspheres with nanowires grown on the inner and outer surfaces (HZMSnws) have been successfully synthesized by a simple two-step thermal process approach, where pre-deposited Zn powder particles on Si substrates act as temporary templates to form hollow ZnO sphere shells, while additional Zn powder acts as a Zn source to grow single crystal nanowires on the surfaces of spherical shells. SEM, XRD, TEM and HRTEM were used to characterize the morphology and crystalline structure of the samples. Photoluminescence (PL) measurement shows strong UV emission (380 nm) of HZMSnws samples. Lacking the need for the additional template removal is an important advantage of this approach over others and it therefore can be used to prepare hollow ZnO nano/microsphere shells (HZMSs) and HZMSnws at low cost and at large scale. These kinds of special high surface area hollow spherical structures may find potential applications in photocatalysis, light-weight composite fillers, acoustic insulation, UV nano/micro-optoemission devices and photoanodes of dye-sensitized solar cells.     

Dependence of the solar cell performance on nanocarbon/Si heterojunctions

Solar cells that combine single-crystalline silicon(Si) with graphene(G) have been widely researched in order to develop next-generation photovoltaic devices. However, the power conversion efficiency(PCE) of G/Si solar cell without chemical doping is commonly low due to the relatively high resistance of graphene. In this work, through combining graphene with carbon nanotube(CNT) networks, we fabricated three kinds of hybrid nanocarbon film/Si heterojunction solar cells in order to increase the PCE of the graphene based Si solar cell. We investigated the characteristics of different nanocarbon film/Si solar cells and found that their performance depends on the heterojunctions. Specifically, a doping-free G-CNT/Si solar cell demonstrated a high PCE of 7.9%, which is nearly equal to the combined value of two individuals(G/Si and CNT/Si). This high efficiency is attributed to the synergistic effect of graphene and CNTs, and can be further increased to 9.1% after applying a PMMA antireflection coating. This study provides a potential way to further improve the Si based heterojunction solar cells.     

银纳米颗粒减反射特性的理论研究

为增强晶体硅太阳电池的光利用效率,提高光电转换效率,研究了金属银纳米颗粒的光学散射性质.基于银纳米粒子表面等离子激元效应和MIE散射理论,采用Matlab数值计算,理论分析了不同银纳米颗粒尺寸和银粒子分布密度对太阳光谱各波长的散射特性.获得了实现高的光透过率所需最佳银纳米颗粒半径范围,研究发现随着银纳米颗粒半径增加,偶极峰红移、高极峰逐渐出现.定量地给出了最佳颗粒分布密度随银粒子半径的变化规律,建立了计算减反射膜透射率的理论方法,找到了银纳米颗粒光学透过率的简单函数表达式,能为实验研究提供理论指导. 关键词： 银纳米颗粒 透过率 MIE理论 太阳电池     

Effect of Ultraviolet Light on Hybrid Zinc Oxide Polymer Bulk Heterojunction Solar Cells

Compared to conjugated polymer poly[2-methoxy-5-（3＇ ,7＇-dimethyloctyloxy）-l,4-phenylenevinylene] （MDMO-PPV） solar cells, bulk heterojunction solar cells composed of zinc oxide （ZnO） nanocrystals and MDMO-PPV have a better energy conversion efficiency. However, ultraviolet （UV） light deteriorates the performance of solar cells composed of ZnO and MDMO-PPV. We propose a model to explain the effect of UV illumination on these ZnO：MDMO-PPV solar cells. According to this model, the degradation from UV illumination is due to a decrease of exciton dissociation efficiency. Our model is based on the experimentM results such as the measurements of current density versus voltage, photoluminescence, and photocurrent.     

Effect of precursor concentration on the growth of zinc oxide nanorod arrays on pre-treated substrates

Well aligned zinc oxide nanorod arrays (ZNAs) synthesized by a simple chemical bath deposition method were fabricated on pre-treated Si substrates. By keeping the molar VI/II ratio constant, the effect of precursor concentration on the growth and optical quality of the ZNAs was investigated. The as-synthesized ZNAs were characterized by field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD) and photoluminescence spectroscopy (PL). FESEM images show that both the diameter and aspect ratio of the ZNAs increase dramatically as the precursor concentration increases. The XRD analysis indicates that all the as-grown ZNAs are crystalline and are preferentially oriented along the c-axis. The high intensity ratio of the UV emission to visible emission in the room temperature PL spectra illustrate that high optical quality ZNAs were produced.     

Study on crystalline properties of Er-Si-O compounds in relation to Er-related 1.54 μm photoluminescence and electrical properties

Er-Si-O crystalline compounds, which exhibit superlattice structures and sharp and strong Er-related 1.54 μm photoluminescence (PL) spectra at room temperature have been formed by self-assembling growth mechanism. Oxidation of the starting materials which have Si and Er at an atomic ratio of 2:1 are prepared and then oxidation and succeeding high-temperature annealing in Ar above 1250 °C cause a self-assembled superlattice-structured Er-Si-O crystalline compounds. The control of the ratio of Si and Er, as well as the following oxidation and annealing processes, is found to be sensitive to the crystalline properties, PL spectra and electrical properties. In this study, Er-Si-O crystalline thin films are formed on Si substrates by sol-gel and MOMBE methods, and their crystalline properties such as crystalline orientation and concentration ratio of Er, Si and O are investigated. Crystalline Er-Si-O films of high orientation are successfully grown on Si(1 0 0) and its inclined surface. The PL and excitation spectra, fluorescence decay and the electrical properties are found to be strongly related to the crystalline properties. Excess O causes a broader 1.54 μm PL spectra, slower fluorescence decay, lower carrier-mediated excitation and higher resistivity. A precise control of O is found to be necessary to grow superlattice-structured Er-Si-O compounds, which are semiconducting and are excitable via carrier-mediated excitation mechanism.     

Broad band light emission from Ag-ion implanted silicon nanocrystals

Silicon nanoparticles formed using low energy (<50 keV) silver ion implantation in crystalline Si exhibit broad band light emission from ultraviolet (UV) to green. The formation of nanoparticles is confirmed using high resolution electron microscopy (HRTEM) and the resulting microscopy is used to obtain the size distribution of Si nanoparticles. Photoluminescence (PL) spectra were observed in the range of the UV to the green. The origin of emission is most likely from highly localized defects at the Si/SiO2 which is further confirmed from Photoluminescence Excitation (PLE) and effective mass theory estimation.     

Advantages of InGaN/GaN multiple quantum well solar cells with stepped-thickness quantum wells

InGaN/GaN multiple quantum well (MQW) solar cells with stepped-thickness quantum wells (SQW) are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density (Jsc) and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G (100 mW/cm2). In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.     

Improved performance of solar cell based on porous silicon surfaces

Porous silicon (PS) surfaces were fabricated by electrochemical etching for both sides of the Si wafer. The objective of the present study is to investigate the PS effect on performance of silicon solar cells. Moreover, enhancement of solar cell efficiency can be obtained by manipulating of the reflected mirrors, and the process is very promising for solar cells manufacturing due to its simplicity, lower cost and suitability for mass production. The surface of PS is observed to have been discrete pores with smooth walls, and with short branches pores for the polished wafer side. In contrast, the etched backside of the wafer was observed to have bigger pore size than the etched polished side, and pores on the surface are in random location. PS formed on the both sides has lower reflectivity value in comparison to the other researcher group. The increase in efficiency of solar cell fabricated with PS formed on both sides of the wafer were extremely observed in comparison to one side PS and bulk silicon solar cells respectively. Solar cell fabricated shows that the conversion efficiency increased to 14.5% in comparison to unetched sample. The porous surface texturing properties could enhance and increased the conversion efficiency of silicon solar cells, these results also showed that the efficiency with this procedure is more promising in comparison to other solar cells, which are fabricated under similar conditions.     

Zinc oxide nanoparticles for improvement of thin film photovoltaic structures’ efficiency through down shifting conversion

The paper presents the idea to improve the performance of thin film photovoltaic cells by a light capture enhancement through the introduction of down shifting energy converters. Luminescent down shifting layers convert high-energy photons (UV light) into low-energy ones (visible light), which are more efficient in a photovoltaic conversion. For this purpose, the application of a thin layer composed of zinc oxide (ZnO) nanoparticles deposited onto a thin film solar cell is proposed. The paper presents both experimental and theoretical results of this approach. Conducted investigations include an analysis of ZnO nanoparticle layers, deposited in two independent technology methods. The results showed that ZnO nanoparticles have a great potential of application as down converting layers and can be implemented to improve the efficiency of photovoltaic cells, especially in the field of thin film PV structures. The proposed new deposition method can potentially be used in some industrial photovoltaic applications.