复合定向凝固法制备多晶硅铸锭

采用复合定向凝固法制备多晶硅铸锭,在精炼和定向凝固过程中施加电磁场控制柱状晶生长过程.实验制得平行于铸锭中心轴的柱状晶,直径约为1mm,铸锭表面质量良好.分析表明金属杂质并未在晶界处发生聚集;且沿铸锭轴向分布也有明显改善,增加了铸锭的有效提纯长度.并通过理论计算探讨了晶体生长速度和定向凝固次数对杂质去除效果的影响.     

Determination of boundary condition of a multi-crystalline silicon billet during continuous casting

Boundary conditions are always complicated and not readily available during continuous casting, especially for the multi-crystalline silicon materials. In order to improve the situation, the temperature variation curves for certain points in the multi-crystalline silicon have been obtained using the experimental apparatus under different cooling conditions. Based on the temperature measurements, the heat transfer coefficients in the second cooling zone and the interface between the multi-crystalline silicon and mould or bottom block have been calculated applying the inverse method and numerical simulation. The calculated results have been validated by comparing the predicted temperatures with the measured ones.     

多晶硅表面制绒技术研究现状

光伏产业在新能源发展规划中占有重要地位,目前多晶硅太阳能电池已经成为太阳能电池市场主流。硅片表面绒面的质量对太阳能电池转换效率有重要影响,多晶硅表面制绒技术也越来越受到世界各国的重视。掌握多晶硅表面制绒技术的原理及特点对提高表面绒面质量十分重要。首先分析多晶硅表面制绒的技术要求,随后根据不同的技术原理,依次对干法制绒技术、湿法制绒技术以及掩膜制绒技术进行综述,详细分析不同制绒技术的技术特点并阐述其应用实例,随后从绒面质量、制绒效率、成本以及环保性等方面对多晶硅制绒技术进行评述,最后对多晶硅制绒技术的发展趋势进行预测。     

熔析结晶法提纯硅工艺研究进展

随着光伏产业的快速发展,对太阳能级硅原材料的需求不断增加。熔析结晶法作为一种冶金硅提纯的新工艺越来越受到重视。熔析结晶法是利用冶金硅中杂质元素的偏析行为,选择适当的熔析介质,使杂质元素从冶金硅中偏析到熔析介质中,进而获得高纯硅的方法。详细介绍了Al-Si、Sn-Si、Cu-Si、Fe-Si和Ca-Si等熔析体系对冶金硅提纯的研究现状,比较了各种介质体系的优缺点。同时针对熔析结晶法提纯硅存在的问题提出了一些建议。     

Ellipsometric study of the influence of chemical etching on thin porous silicon structures

The effect of chemical etching on Porous Silicon (PS) samples is studied and quantified by using variable angle spectroscopic ellipsometry (VASE). The main aim of this work is to assess the impact of such etching on the physical properties of electrochemically etched, thin PS antireflection coatings (ARC) for solar cell applications. In this study, detailed models of PS layers etched at constant current densities are created using a graded uniaxial Bruggeman Effective Medium Approximation (BEMA). Changes in porosity, thickness, and optical anisotropy of the PS samples due to chemical etching are determined as a function of etching time after PS formation. Three series of PS films, etched at three different current densities, are investigated. It is shown that significant changes in physical properties occur for chemical etching times longer than ~ 60 s. The anodic etching process for fabricating PS ARC structures can be performed in less than 10 s. Therefore, chemical etching does not lead to significant deviations from the intended PS structure and is not seen as a hindrance to accurate control of processes for fabricating thin PS ARCs.     

A Grain Orientation-Independent Single-Step Saw Damage Gettering/Wet texturing Process for Efficient Silicon Solar Cells

Improving electrical and optical properties is important in manufacturing high-efficiency solar cells. Previous studies focused on individual gettering and texturing methods to improve solar cell material quality and reduce reflection loss, respectively. This study presents a novel method called saw damage gettering with texturing that effectively combines both methods for multicrystalline silicon (mc-Si) wafers manufactured using the diamond wire sawing (DWS) method. Although mc-Si is not the Si material currently used in photovoltaic products, the applicability of this method using the mc-Si wafers as it contains all grain orientations is demonstrated. It utilizes saw damage sites on the wafer surfaces for gettering metal impurities during annealing. Additionally, it can crystallize amorphous silicon on wafer surfaces generated during the sawing process to allow conventional acid-based wet texturing. This texturing method and annealing for 10 min allow for the removal of metal impurities and effectively forms a textured DWS Si wafer. The results show that the open-circuit voltage (ΔV_oc = +29 mV), short-circuit current density (ΔJ_sc = +2.5 mA cm⁻²), and efficiency (Δη = +2.1%) improved in the p-type passivated emitter and rear cells (p-PERC) manufactured using this novel method, as compared to those in the reference solar cells.     

碳离子注入对硅片微摩擦学行为的影响

对单晶硅片进行不同剂量的碳离子注入,测量碳离子注入前后硅片的纳米硬度、弹性模量、硅表面与探针之间的摩擦系数和划痕深度以及硅片与Si3N4球的摩擦磨损,研究试样在过程中摩擦系数及磨损量的变化.结果表明,碳离子注入可能导致硅片表面结构的改变,从而影响了力学性能,但改善了微摩擦学特性.碳离子注入剂量为2×1015 ions/cm2时硅片的纳米硬度和弹性模量都明显降低,但其划痕摩擦系数和划痕深度均大于未注入硅片;碳离子注入后硅片的减摩效果和耐磨性能在小载荷下得到了大幅度提高,当载荷达到一定值后,摩擦系数迅速增加并产生磨损痕迹.其磨损机制在小载荷下以粘着磨损为主,在大载荷下以材料的微疲劳和微断裂为主.     

溅射法低温生长纳米硅薄膜及异质结电池

用射频溅射法在P型硅衬底上生长了纳米硅薄膜,衬底温度控制在100℃左右,工作气体选用H2 Ar,氢气的分压控制在31%到73%,同时改变薄膜的沉积时间.用Raman、XRD、AFM、SEM 及椭偏仪对薄膜的特性进行了测定.XRD的测试结果表明,样品中存在一种微结构,不同于用PECVD方法生长的薄膜.椭偏仪的测试结果给出这种薄膜具有宽带隙.在室温条件下对异质结薄膜电池的I-V特性进行了测量.     

Study for amorphous silicon etching process using dielectric barrier discharge

Characteristics of amorphous silicon (a-Si) etching using atmospheric pressure plasma discharge had been studied. Dielectric barrier discharge (DBD) plasma with nitrogen gas was employed for the study. The active chemical agent for etching was generated by mixing a small quantity of sulfur hexafluoride (SF₆) gas into the plasma. The two distinguishable plasma zones are generated with the specially designed DBD plasma generator. The one is the main discharge zone generated between the two parallel plate electrodes. And the other one is downstream plasma zone extracted from the main discharge zone through the holes perforated on the bottom electrode. A test specimen was etched located at the plasma zone and moved the zone several times for etching on a temperature controlled stage. The etch rate of a-Si and the selectivity to silicon nitride (SiNx) were improved by addition of hydrogen (H₂) or methane (CH₄) gas into the plasma. However, when the specimen temperature was lower than 100 °C with H₂ or CH₄ gas added plasma condition, a-Si layer was not etched at all, but in the range of 100-140 °C of specimen temperature, the a-Si layer started to be etched while the influence of the specimen temperature on etching of a-Si was ignorable in that temperature range. At the optimized condition, the a-Si etch rate was up to 3000 A/min in the downstream plasma zone with the 3 mm of the distance between the surface of the specimen and the bottom side of the DBD plasma generator module. And the etch rate ratio between a-Si and SiNx was more than 100:1.     

不同掺锗浓度对多晶硅性能的影响

研究不同的掺锗浓度对硼掺杂P型多晶硅铸锭性能的影响。实验结果表明:掺锗能够影响多晶硅铸锭中的位错密度、间隙氧浓度和硅片的机械强度。当掺锗浓度低于5×1019 at·cm-3时,位错密度和间隙氧浓度随着掺锗浓度的增加而降低,机械强度则随着掺锗浓度的增加而增强。当铸锭中掺锗浓度为5×1019 at·cm-3时,与不掺锗的硅片相比,掺锗硅片中位错密度平均降低约3%,间隙氧浓度平均降低约6%,机械强度平均提高约20%。但是,当掺锗浓度高于1×1020 at·cm-3时,掺锗对多晶硅铸锭性能的改善效果变差了,并对其性能产生不利的影响。     

硅圆片表面活化工艺参数优化研究

利用正交实验,对单晶硅表面活化工艺中重要参数对活化效果的影响进行了研究,并优化了工艺.实验针对RCA活化溶液处理工艺的特点,选择溶液配比、处理时间和温度3个重要因素为研究对象,以30%盐水为测试液,以接触角为指标,评估了这3个因素对活化效果的影响规律.对实验结果的分析表明,在此三因素中,活化温度与活化效果的关系最密切,...     

感应加热硅衬底上的金膜用于圆片键合

选用垂直于其表面的射频磁场对镀金膜的硅片进行了感应加热,由于磁场对材料加热具有选择性,感应热量首先作用于硅片上的金膜内,硅片先被传导加热到一定温度,然后被感应加热.理论上分析了该方法的可行性,初步试验结果表明,虽然金膜厚度低于感应趋肤深度,但在没有应用感应加热基座的情况下,几秒钟内就形成了金硅共晶相.另外,升温速度快,有效减少了加热过程中金对硅的扩散影响,该方法可广泛用于微系统封装中的圆片键合.     

Influence of process steps on the performance of microcrystalline silicon thin film transistors

Bottom gate microcrystalline silicon thin film transistors (μc-Si TFT) have been realized with two types of films: μc-Si(1) and μc-Si(2) with crystalline fraction of 80% and close to 100% respectively. On these TFTs we applied two types of passivation (SiN_x and resist). μc-Si TFTs with resist as a passivation layer present a low leakage current of about 2.10^− 12 A for V_G = − 10 and V_D = 0.1V an ON to OFF current ratio of 10⁶, a threshold voltage of 7 V, a linear mobility of 0.1 cm²/V s, and a sub-threshold voltage of 0.9 V/dec. Microcrystalline silicon TFTs with SiN_x as a passivation present a new phenomenon: a parasitic current for negative gate voltage (− 15 V) causes a bump and changes the shape of the sub-threshold region. This excess current can be explained by and oxygen contamination at the back interface.     

A hybrid tandem solar cell based on hydrogenated amorphous silicon and dye-sensitized TiO2 film

Hydrogenated amorphous silicon film (a-Si:H) as top cell is introduced to dye-sensitized titanium dioxide nanocrystalline solar cell (DSSC) as bottom cell to assemble a hybrid tandem solar cell. The hybrid tandem solar cell fabricated with the thicknesses a-Si:H layer of 235 nm, ZnO/Pt interlayer of 100 nm and DSSC layer of 8.5 μm achieves a photo-to-electric energy conversion efficiency of 8.31%, a short circuit current density of 10.61 mA·cm^− 2 and an open-circuit voltage of 1.45 V under a simulated solar light irradiation of 100 mW·cm^− 2.     

Band gap profiles of intrinsic amorphous silicon germanium films and their application to amorphous silicon germanium heterojunction solar cells

Intrinsic amorphous silicon germanium (i-a-SiGe:H) films with V, U and VU shape band gap profiles for amorphous silicon germanium (a-SiGe:H) heterojunction solar cells were fabricated. The band gap profiles of i-a-SiGe:H were prepared by varying the GeH₄ and H₂ flow rates during the deposition process. The use of i-a-SiGe:H with band gap profile in an absorber layer for a-SiGe:H heterojunction solar cells was investigated. The solar cell using a VU shape band gap profile shows a higher efficiency compared to other shapes. The highest efficiency obtained for an a-SiGe:H heterojunction solar cell using the VU shape band gap profile technique was 9.4% (V_oc = 0.79 V, J_sc = 19.0 mA/cm² and FF = 0.63).     

籽晶粒径分布对高效多晶硅晶体生长的影响

采用不同粒径分布的单晶籽晶进行高效多晶硅铸锭,结果表明单晶籽晶的粒径分布对引晶效果影响显著.籽晶粒径在1～4mm范围时,引晶效果最佳;粒径大于4mm时,硅熔体流延现象的存在导致长晶初期晶体中位错密度偏高,少子寿命降低;粒径小于1 mm时,细小的形核点也会影响晶体中的位错密度和少子寿命.对应电池片效率的结果也验证了该结论.     

Role of metal and dielectric nanoparticles in the performance enhancement of silicon solar cells

The suitability of using spherical metal and dielectric nanoparticles on the top of a silicon solar cell has been investigated. An enhancement index factor (EIF) for each wavelength of light and an averaged EIF for the AM 1.5 solar spectrum, weighted by the photon flux, has been introduced. These factors estimate the effect of the nanoparticles in improving the performance of the solar cells, considering the absorption loss due to joule heating, fraction of radiation scattered into the substrate and the front scattered radiation pattern. A systematic comparison between silver and dielectric nanoparticles (silica, silicon nitride, titanium dioxide) shows that titanium dioxide and silicon nitride nano particles of sizes ≥100?nm exhibit larger enhancements compared to that of silver nanoparticles of similar sizes. Further, as the dielectric constant of the dielectric nanoparticles increases, the optimal particle size corresponding to maximal enhancement shifts towards lower value. At optimal particle sizes, the enhancement is 1.5–2 times greater than that due to silver nanoparticles.     

Optical emission spectroscopy as a process control tool during plasma enhanced chemical vapor deposition of microcrystalline silicon thin films

The decisive criterion associated with the species emission intensity ratio (Hα/SiH*) which characterizes the crystallinity of microcrystalline silicon (μc-Si) film was found to display an unstable behavior resulting from species concentration variation during μc-Si film growth with optical emission spectroscopy (OES) tool. In this study, a real-time process control system i.e. closed-loop system was developed. It aims to control the species intensity ratio with OES device in a very high frequency (VHF) plasma enhanced chemical vapor deposition reactor, via modulating the VHF power and silane dilution to improve μc-Si film growth for high efficiency a-Si/μc-Si tandem solar cell. The experiment results show that the closed-loop system stabilized the Hα/SiH* intensity ratio within a variation of 5% during the μc-Si film deposition process. Higher growth rate of μc-Si film with the same crystallinity was obtained in the closed loop system which consumed less power and SiH4 gas than in the open loop system, i.e. without process control.     

Influence of working pressure on ZnO:Al films from tube targets for silicon thin film solar cells

Mid-frequency magnetron sputtering of aluminum doped zinc oxide films (ZnO:Al) from tube ceramic targets has been investigated for silicon based thin film solar cell applications. The influence of working pressure on structural, electrical, and optical properties of sputtered ZnO:Al films was studied. ZnO:Al thin films with a minimum resistivity of 3.4 × 10⁻⁴ Ω cm, high mobility of 50 cm²/Vs, and high optical transmission close to 90% in visible spectrum region were achieved. The surface texture of ZnO:Al films after a chemical etching step was investigated. A gradual increase in feature sizes (diameter and depth) was observed with increasing sputter pressure. Silicon based thin film solar cells were prepared using the etched ZnO:Al films as front contacts. Energy conversion efficiencies of up to 10.2% were obtained for amorphous/microcrystalline silicon tandem solar cells.