晶体硅电池表面钝化的研究进展

随着晶体硅太阳电池技术的不断发展,硅片的厚度不断降低,电池表面钝化对提高太阳能电池转化效率变得尤为重要。本文介绍了表面钝化膜在晶体硅太阳电池中的应用,以及几种晶体硅电池表面钝化方法,包括等离子体增强化学气相沉积法、氢化非晶硅、热氧化法、原子层沉积法以及叠层钝化,并分别介绍了它们在应用上的优缺点。分析了制备钝化膜过程中存在的问题,并提出了相应措施及发展趋势。表面钝化技术是提高晶体硅电池转换效率最有效的手段之一,今后晶体硅电池表面钝化技术仍将是国内和国际研究的热点之一。     

快速热氧化制备超薄二氧化硅层及其钝化效果

二氧化硅(SiO2)是制备高效晶体硅太阳电池常用的钝化手段。本文利用快速热氧化(RTO)技术在晶体硅表面制备超薄SiO2层,考察其对硅表面的钝化作用。在100%O2气氛下,900℃RTO处理180s,可以使样品的少子寿命达到146.6μs的最佳值。采用RTO方法制备的SiO2薄膜厚度可以控制在几个纳米范围。通过与等离子体增强化学气相沉积(PECVD)系统沉积的氮化硅(SiNx)薄膜形成叠层钝化膜,可以进一步提高对太阳电池表面的钝化效果。单层SiNX薄膜钝化的样品有效载流子寿命为51.67μs,SiO2/SiNx叠层薄膜钝化的样品有效载流子寿命提高到151.18μs。     

a-Si:H基薄膜中SiH及SiH_2键构成对n型直拉单晶硅片钝化效果的影响研究

n型单晶硅表面本征非晶硅基薄膜(a-Si∶H)的钝化作用是高效率非晶硅/晶体硅异质结太阳电池的关键。本文采用掺氧和热处理的方式改变本征非晶硅基薄膜(a-Si∶H)样品中Si H和Si H2键构成,利用Sinton WCT-120少子寿命测试仪及傅里叶红外光谱测试仪分析样品性能,研究Si H和Si H2键构成对n型直拉单晶硅片(n-Cz-Si)表面钝化效果的影响。结果表明:1掺氧和热处理均会增加a-Si∶H中Si H2键相对于Si H键的比例;2在200~350℃范围内,随着热处理温度的升高,薄膜中Si H2键相对于Si H键的比例增加,薄膜对n-Cz-Si的钝化效果先变好,在275℃时达到极值后变差;3a-Si∶H薄膜中Si H2键和Si H键的相对含量对n-Cz-Si表面的钝化效果有直接的影响,根据实验结果,Si H2与Si H键相对含量在一定范围时钝化效果最好,过高或过低均不利于钝化。     

上海高研院金属氧化物/硅异质结太阳电池研究取得进展

<正>近日,中国科学院上海高等研究院联合晋能清洁能源科技股份公司,在新型金属氧化物/硅异质结太阳电池研究中取得进展。光生载流子的空间有效分离和收集是晶体硅以及其他类型光伏器件的核心问题之一。在晶体硅表面形成载流子选择性接触层,允许一种载流子通过,而对另一种载流子起阻挡作用。相对传统的扩散掺杂技术,选择性接触层可以减缓重掺杂带来的不利因素(如俄歇复合、带宽变窄)。基于载流子选择性接触原理,非晶硅/晶体硅异质结电池已实现     

20世纪90年代世界光伏技术及产业的发展回顾

自20世纪50年代研制成第1块实用的硅太阳电池、60年代太阳电池进入空间应用、70年代进入了地面应用，太阳能光电技术已历经了半个世纪。目前占主流的太阳电池是硅太阳电池，它又分单晶硅太阳电池、多晶硅太阳电池(总称晶体硅太阳电池)和非晶硅太阳电池。此外，还有CaAs太阳电     

异质结太阳能电池的仿真模拟研究和界面态密度对效率的影响

大量文献已经报道非晶硅/晶体硅异质结电池每层材料的参数对电池的影响,如厚度、掺杂浓度等,但是并没有进一步给出透明导电氧化物薄膜TCO的功函数对电池的影响以及如何选择合适的TCO,也很少有报道界面态密度对异质结太阳能电池的影响机理。本研究表明,对于n型单晶硅片为衬底的异质结电池,发射场的TCO功函数越大越好,最佳范围是5.4～6.3 eV。对于背场的TCO功函数越小越好,最佳范围是3.6～4.0 eV。另外研究表明,对于n型衬底的非晶硅/晶体硅异质结电池(HIT电池),与衬底背面与非晶硅的界面态(Dit2)相比,衬底前表面与非晶硅的界面态(Dit1)是影响电池性能的主要因素,并且Dit1和Dit2态中,与类施主态相比,对电池效率起到主要影响作用的都是类受主态。     

HWCVD法掺氧氢化非晶硅(a-SiO_x:H)钝化n-Cz-Si研究

HIT电池高效率核心技术之一为本征非晶硅薄膜钝化硅片。本文采用热丝化学气相沉积(HWCVD)法制备a-SiO_x:H,采用SintonWCT-120少子寿命测试仪、光谱型椭偏仪及傅里叶红外光谱测试仪分析样品性能,以期获得高质量a-SiO_x:H的工艺参数并分析微观机理。结果表明:①随热丝电流增加,沉积a-SiO_x:H膜的样品少子寿命先增加后减小,22.5 A时钝化效果最好,少子寿命高达2530μs,表面复合速率降至3.6 cm/s;②本实验结果中,a-SiO_x:H钝化效果明显优于a-Si:H,少子寿命最高分别为2530和547μs;③a-SiO_x:H薄膜中SiH、SiH_2相对含量与薄膜钝化性能无直接关联。     

衬底温度对氢化非晶氧化硅(i-a-SiOx:H)钝化性能的影响研究

本征氢化非晶氧化硅(i-a-SiO_x:H)是a-Si:H/c-Si异质结太阳电池中重要的钝化材料之一。本文采用PECVD法研究不同沉积衬底温度下n-Cz-Si表面沉积i-a-SiO_x:H的钝化性能,采用微波光电导(MW-PCD)和射频光电导(RF-PCD)两种方法测试硅片少子寿命,光谱型椭偏仪检验沉积薄膜的晶型。结果表明：(1)椭偏仪结果显示实验所沉积薄膜为所需非晶型;(2)MW-PCD与RF-PCD法测试均显示,n-Cz-Si双面室温(25℃)沉积i-a-SiO_x:H后硅片少子寿命很低,随沉积衬底温度升高硅片少子寿命先增加后减少,25℃少子寿命最低,200℃～220℃(不同位置略有差别)少子寿命最高、钝化效果最优。     

晶体硅电池产业化高效技术分析

毫无疑问,硅电池是促进光伏产业前进的中坚力量。而太阳电池组件中,大约80%的电力都来源于晶体硅组件。第一个晶体硅电池出现在1954年,恰宾和卡尔松等人在贝尔实验室用表面抛光的硅片制作PN结,然后分别在两侧蒸镀上金属电极,就制成了光伏转换效率达6%的世界上第一块实用性硅太阳电池,成为现代硅太阳电池时代的开始。经过几十年的发展,晶体硅太阳电池经历了几个快速发展期,效率得到不断攀升,从最初的8%提升至目前的25%(实验室效率),正如图1所示。很多实验室技术在经过多年开发后走向了产业,带动了很多新型产业化高效电池的出现,这些电池的产业化平均效率分别达到了18%(美国Innovalight公司的硅墨水技     

n型晶体硅太阳电池最新研究进展的分析与评估

n型晶体硅具有体少子寿命长、无光致衰减等优点,非常适合制作高效低成本太阳电池.结合PC1D模拟,对n型晶体硅太阳电池的最新研究成果进行了分析,指出n型晶体硅太阳电池要实现产业化必须先解决p型硅表面钝化、硼扩散和硼发射极金属化等问题.最后预测了n型晶体硅太阳电池的产业化前景.     

Thin-film polycrystalline silicon solar cells formed by flash lamp annealing of a-Si films

We have fabricated thin-film solar cells using polycrystalline silicon (poly-Si) films formed by flash lamp annealing (FLA) of 4.5-µm-thick amorphous Si (a-Si) films deposited on Cr-coated glass substrates. High-pressure water-vapor annealing (HPWVA) is effective to improve the minority carrier lifetime of poly-Si films up to 10 µs long. Diode and solar cell characteristics can be seen only in the solar cells formed using poly-Si films after HPWVA, indicating the need for defect termination. The actual solar cell operation demonstrated indicates feasibility of using poly-Si films formed through FLA on glass substrates as a thin-film solar cell material.     

T型发射区单晶硅太阳电池的输出特性研究

利用TCAD半导体器件仿真软件对具有T型发射区结构的单晶硅太阳电池进行了仿真研究。全面系统地分析了在不同衬底少子寿命情况下,不同T型发射区深度对太阳电池外量子效率、短路电流密度、开路电压、填充因子及转换效率的影响。仿真结果表明:采用T型发射区结构可在一定程度上提高常规均匀发射区太阳电池的电学性能;T型发射区结构对700~1200nm长波段入射光的外量子效率具有明显的改善作用;当衬底少子寿命一定时,太阳电池短路电流密度、填充因子均随T型发射区深度的增大而增大,而开路电压随T型发射区深度的增大而减小;当T型发射区深度大于80μm时,对于低衬底少子寿命的单晶硅太阳电池,T型发射区结构对其转换效率的改善效果最为显著。     

多孔硅对单晶硅少子寿命影响状况的研究

以p型单晶硅片为研究对象,在单晶硅片表面采用化学腐蚀方法制备多孔硅层,通过实验选取制备多孔硅的最佳工艺条件,采用SEM观察多孔硅表面形貌,以及用微波光电导法测试少子寿命的变化情况。结果表明,在相同的腐蚀溶液配比条件下腐蚀11min得到的多孔硅层的表面形貌最好,孔隙率最大。在850℃下热处理150min时样品少子寿命的提高达到最大,不同腐蚀时间的样品少子寿命提高程度不同,腐蚀11min的样品少子寿命提高最大,约有10%左右。多孔层的形成伴随着弹性机械应力的出现,引起多孔层-硅基底界面处产生弹性变形,这有利于缺陷和金属杂质在界面处富集。另外,多孔硅仍具有晶体结构,但其表面方向上的晶格参数要比初始硅的晶格参数大,也有利于金属杂质向多孔层迁移。     

Interaction between process technology and material quality during the processing of multicrystalline silicon solar cells

Multicrystalline silicon is the most used material for the production of silicon solar cells. The quality of the as grown material depends on the quality of the feedstock and the crystallization process. Bulk impurities, crystal defects like dislocations and of course the grain boundaries determine the material quality and thus the solar cell conversion efficiency. Therefore minority carrier lifetime measurements are often done to characterize the material quality. But the measured values are from limited use because it is known that the solar cell process itself can dramatically change the minority carrier lifetime and the solar cell efficiency. In order to obtain more detailed information of the behaviour of different defect types additionally high-resolution LBIC (light beam induced current)-measurements have been done. Since LBIC needs a pn-junction for photocurrent generation the LBIC technique has been combined with the a-Si/c-Si heterojunction cell process, which makes it possible to manufacture solar cells even from as cut wafers without changing the material quality. With this combination of measurement and preparation techniques it was possible to analyze the influence of the diffusion process and the firing process on the behaviour of the three different defect types: grain boundaries, dislocation networks and bulk impurities.     

Porous silicon and aluminum co-gettering experiment in p-type multicrystalline silicon substrate

The lifetimes of non-equilibrium minority carriers, which bound with the diffusion length, are considered as two important parameters of the low-quality multicrystalline silicon (mc-Si) substrate. Its value defines the quality of the initial substrate. It is also subjected to change as a result of many high-temperature operations during the device fabrication. Therefore, it is necessary to incorporate certain processing steps that either improve or preserve the electronic quality of the mc-Si substrate. In this study, a novel porous silicon and aluminum co-gettering experiment has been applied as a beneficial approach to improve the electronic quality of the low-resistivity mc-Si substrates. Porous silicon layers were prepared by anodization of the n⁺ silicon region by a simple electrochemical etching process using an aqueous HF-based electrolyte, which leads to the creation of porous silicon microcavities. Besides making porous silicon and aluminum co-gettered samples, both phosphorous and aluminum alloy-gettered samples and reference samples were made. The gettering-induced lifetime enhancement in the test samples was monitored by measuring the lifetime/diffusion length of the test samples using two independent methods such as photoconductivity decay (PCD) measurement and the photocurrent generation method (PCM), respectively. The result in both the measurements has shown a reasonably good agreement with each other. Therefore, it is inferred that the applied co-gettering experiment has a synergetic effect to improve the lifetime of the mc-Si substrate.     

Porous silicon and aluminum co-gettering experiment in p-type multicrystalline silicon substrate

The lifetimes of non-equilibrium minority carriers, which bound with the diffusion length, are considered as two important parameters of the low-quality multicrystalline silicon (mc-Si) substrate. Its value defines the quality of the initial substrate. It is also subjected to change as a result of many high-temperature operations during the device fabrication. Therefore, it is necessary to incorporate certain processing steps that either improve or preserve the electronic quality of the mc-Si substrate. In this study, a novel porous silicon and aluminum co-gettering experiment has been applied as a beneficial approach to improve the electronic quality of the low-resistivity mc-Si substrates. Porous silicon layers were prepared by anodization of the n⁺ silicon region by a simple electrochemical etching process using an aqueous HF-based electrolyte, which leads to the creation of porous silicon microcavities. Besides making porous silicon and aluminum co-gettered samples, both phosphorous and aluminum alloy-gettered samples and reference samples were made. The gettering-induced lifetime enhancement in the test samples was monitored by measuring the lifetime/diffusion length of the test samples using two independent methods such as photoconductivity decay (PCD) measurement and the photocurrent generation method (PCM), respectively. The result in both the measurements has shown a reasonably good agreement with each other. Therefore, it is inferred that the applied co-gettering experiment has a synergetic effect to improve the lifetime of the mc-Si substrate.     

Influence of stain etching on low minority carrier lifetime areas of multicrystalline silicon for solar cells

In this work the use of HF/HNO₃ solutions for texturing silicon-based solar cell substrates by stain etching and the influence of texturing on minority carrier lifetimes are studied. Stain etching is currently used to decrease the reflectance and, subsequently improve the photogenerated current of the cells, but also produces nanostructures on the silicon surface. In the textured samples it has been observed that an improvement on the minority carrier lifetime with respect to the samples treated with a conventional saw damage etching process is produced on grain boundaries and defects, and the origin of this effect has been discussed.     

TCAD simulations for thin film solar cells with nanoplate structures

The novel thin film solar cell with a nanoplate structure that can solve the conflict between the light absorption and the carrier transport in amorphous silicon thin film solar cell was investigated by TCAD simulations. This new structure has n-type amorphous silicon nanoplate array on the substrate, and p-type amorphous silicon-carbon as window layer and intrinsic amorphous silicon as absorption layer are sequentially grown along the surface of each n-type amorphous silicon nanoplate. Under AM 1.5 G sunlight illumination, the light is absorbed along the vertical direction of nanoplate while the carrier transport is along the horizontal direction. Therefore, nanoplate with the larger height can absorb most of the sunlight. The advantage of this novel structure is that the thickness of the solar cell can be used as thin as possible for effective transport of photo-generated carriers in comparison with the planer one.     

Impact of a-Si:H hydrogen depth profiles on passivation properties in a-Si:H/c-Si heterojunctions

We explore the (near-)interface structure of amorphous/crystalline silicon (a-Si:H/c-Si) heterojunctions as employed in high-efficiency heterojunction solar cells. We make use of secondary-ion-mass-spectroscopy profiles and minority carrier lifetime measurements taken on undoped deuterated amorphous silicon [(i)a-Si:D] layers deposited on c-Si from deuterated silane at identical conditions as the hydrogenated layers we have analyzed previously [T. F. Schulze et al., Appl. Phys. Lett. 96 (2010) 252102]. We briefly discuss the implications of the local interface structure for the c-Si surface passivation as well as for the heterojunction band offsets, and identify a route towards optimization of (i)a-Si:H layers as passivating buffers in a-Si:H/c-Si high-efficiency heterojunction solar cells.