Large‐area epitaxial silicon solar cells based on industrial screen‐printing processes

Thin‐film epitaxial silicon solar cells are an attractive future alternative for bulk silicon solar cells incorporating many of the process advantages of the latter, but on a potentially cheap substrate. Several challenges have to be tackled before this potential can be successfully exploited on a large scale. This paper describes the points of interest and how IMEC aims to solve them. It presents a new step forward towards our final objective: the development of an industrial cell process based on screen‐printing for > 15% efficient epitaxial silicon solar cells on a low‐cost substrate. Included in the discussion are the substrates onto which the epitaxial deposition is done and how work is progressing in several research institutes and universities on the topic of a high‐throughput epitaxial reactor. The industrial screen‐printing process sequence developed at IMEC for these epitaxial silicon solar cells is presented, with emphasis on plasma texturing and improvement of the quality of the epitaxial layer. Efficiencies between 12 and 13% are presented for large‐area (98 cm²) epitaxial layers on highly doped UMG‐Si, off‐spec and reclaim material. Finally, the need for an internal reflection scheme is explained. A realistically achievable internal reflection at the epi/substrate interface of 70% will result in a calculated increase of 3 mA/cm² in short‐circuit current. An interfacial stack of porous silicon layers (Bragg reflectors) is chosen as a promising candidate and the challenges facing its incorporation between the epitaxial layer and the substrate are presented. Experimental work on this topic is reported and concentrates on the extraction of the internal reflection at the epi/substrate interface from reflectance measurements. Initial results show an internal reflectance between 30 and 60% with a four‐layer porous silicon stack. Resistance measurements for majority carrier flow through these porous silicon stacks are also included and show that no resistance increase is measurable for stacks up to four layers. Copyright © 2005 John Wiley & Sons, Ltd.     

基于纳米颗粒的铜锌锡硫硒薄膜制备

采用热注入法制备了Cu2ZnSnS4(CZTS)纳米颗粒,并形成高分散、稳定的"墨水",采用滴注方法形成CZTS前驱体薄膜。利用X射线衍射(XRD)、拉曼光谱(Raman)、透射电子显微镜(TEM)和紫外-可见光谱(UV-VIS)对CZTS纳米颗粒的晶体结构、表面形貌和带隙进行了表征。Raman数据显示合成的纳米颗粒为纯的CZTS,不存在ZnS和Cu2SnS3等杂相。傅里叶红外光谱(FTIR)和UV-VIS表明合成的CZTS纳米颗粒表面被油胺(OLA)包覆,并且其带隙为1.52 eV。对CZTS前驱体薄膜在硫化氢气氛和固态硒气氛中退火处理,得到铜锌锡硫硒(CZTSSe)薄膜。结果表明,经硫化氢处理后薄膜表面平整但CZTS晶粒并没长大,而经过固态硒处理后得到了结晶质量较好的CZTSSe薄膜。     

两种离子束方法制备Cr膜的分析研究

在室温下,采用离子束溅射同时经100 keV Ar 离子轰击的动态离子束混合技术和采用离子束溅射技术这两种方法制备Cr膜,并用XPS,SEM及AES对薄膜的结构、表面形貌、薄膜与基体附着力的影响等进行分析对比。结果表明,与离子束溅射技术制备的Cr膜相比较,动态离子束混合技术制备的Cr膜表面平滑,膜致密呈无气隙的柱状结构,且薄膜元素与基体元素混合形成的组分过渡层较宽,因而有效地提高了Cr膜的附着力。     

sol-gel法制备的ZnO:(Al,La)透明导电膜光电性能

通过X射线衍射、紫外–可见分光光度计、扫描电镜和四探针仪分析等手段,考察了退火温度对ZnO:(Al,La)薄膜微观结构、光学和电学性能的影响,Al掺杂浓度对电阻率的影响。结果表明:随退火温度的升高,薄膜(002)晶面择优取向生长增强,平均晶粒尺寸增大,电阻率降低,透光率上升。在x(Al)为1%,退火温度550℃时,薄膜最低电阻率为1.78×10–3?·cm,平均透光率超过85%。     

Morphology Transformation Pathway of Block Copolymer-Directed Cooperative Self-Assembly of ZnO Hybrid Films Monitored In Situ during Slot-Die Coating

Cooperative self-assembly (co-assembly) of diblock copolymers (DBCs) and inorganic precursors that takes inspiration from the rich phase separation behavior of DBCs can enable the realization of a broad spectrum of functional nanostructures with the desired sizes. In a DBC assisted sol–gel chemistry approach with polystyrene-block-poly(ethylene oxide) and ZnO, hybrid films are formed with slot-die coating. Pure DBC films are printed as control. In situ grazing-incidence small-angle X-ray scattering measurements are performed to investigate the self-assembly and co-assembly process during the film formation. Combining complementary ex situ characterizations, several distinct regimes are differentiated to describe the morphological transformations from the initially solvent-dispersed to the ultimately solidified films. The comparison of the assembly pathway evidences that the key step in the establishment of the pure DBC film is the coalescence of spherical micelles toward cylindrical domains. Due to the presence of the phase-selective precursor, the formation of cylindrical aggregates in the solution is crucial for the structural development of the hybrid film. The pre-existing cylinders in the ink impede the domain growth of the hybrid film during the subsequent drying process. The precursor reduces the degree of order, prevents crystallization of the PEO block, and introduces additional length scales in the hybrid films.     

ULSI化学机械抛光的研究与展望

随着半导体行业的飞速发展，集成电路特征尺寸的微细化，半导体薄膜表面的高平坦化对器件高性能、低成本、高成品率有着重要的影响。作为唯一能实现全局平坦化方法的化学机械抛光(CMP)，近年来发展迅速，应用广泛。文章综述了化学机械抛光技术的发展现状：包括化学机械抛光设备、抛光液、抛光机理模型及应用研究进展；在此基础上，对CMP下一步发展的方向及其应用前景进行了展望。     

各向异性导电胶膜新型填充粒子的研究

用分散聚合法合成了直径为3μm左右的聚苯乙烯核,在核表面化学镀形成带小突起的镍合金导电层,制成ACF新型填充粒子,对聚合物核做了粒径分布、比表面积测试,对核以及导电微球做了环境扫描电镜(ESEM)测试。结果表明:制备的导电微球密度小,呈单分散,镀层结构致密,镀层表面形成了近球形、锥形及其它不定形突起。这些突起可以刺穿电极的氧化膜。实践证明通过控制工艺参数实现控制镀层结构是一条可行方法。     

La0.5Sr0.5CoO3的化学溶液淀积法制备与表征及其应用

采用化学溶液淀积法制备了具有纯钙钛矿结构和良好导电性能的La_(0.5)Sr_(0.5)CoO_3(LSCO)薄膜。LSCO的电阻率随着退火温度的升高、退火时间的增长和厚度增加而减小。650°C退火可以得到7mΩ·cm的电阻率。分别在LSCO和Pt衬底上制备了Bi_4Ti_3O_(12)(BTO)薄膜,分析结果表明,使用LSCO衬底对BTO的析晶有影响,击穿电压、铁电特性均有较大改善。     

光波在具有柱状结构的双折射薄膜中的传输特性

根据电磁场理论的矩阵分析方法推导了光波在具有柱状结构的双轴薄膜中的反射系数、透射系数和相位关系等光学特性.这些关系包含了界面处的多点反射,可以推广到一般的各向异性的多层膜系统.给出了各向同性入射媒质-双轴各向异性膜层-各向同性基底薄膜系统的计算结果,验证了该计算方法的可行性,为双折射多层膜结构及其器件的理论分析和设计提供了理论参考.     

Electrical and optical properties of deep ultraviolet transparent conductive Ga2O3/ITO films by magnetron sputtering

Ga2O3/ITO films were prepared by magnetron sputtering on quartz glass substrates. The transmittance and sheet resistance of ITO films and Ga2O3/ITO films were measured by using a double beam spectrophotometer and four point probes. The effect of the ITO layer and Ga2O3 layer thickness on the electrical and optical properties of Ga2O3/ITO bi-layer films were investigated in detail. Ga2O3 (50 nm)/ITO (23 nm) films exhibited a low sheet resistance of 323 Ω/□ and high deep ultraviolet transmittance of 77.6% at a wavelength of 280 nm. The ITO layer controls the ultraviolet transmittance and sheet resistance of Ga2O3/ITO films. The Ga2O3 layer thickness has a marked effect on the transmission spectral shape of Ga2O3/ITO films in the violet spectral region.