应用高压高功率的微晶硅薄膜高速沉积

应用高压高功率(hphP)甚高频等离子增强化学气相沉积(VHF-PECVD)法对微晶硅(μc-Si:H)进行高速沉积,确定了hphP VHF-PECVD法沉积μc-Si:H的最优条件参数,在此参数下对hphP和低压低功率(IplP)两组样品沉积速率、光电导、暗电导及光敏性等性能参数进行测试,得到了1.58 nm的较高沉...     

单室沉积本征微晶硅薄膜及其在电池中的应用

为获得单室沉积高效微晶硅(μc-Si)太阳电池,首先采用甚高频等离子体增强化学气相沉积(VHF-PECVD)技术制备了不同沉积条件下的本征μc-Si薄膜.通过对材料的结构和电学输运特性的研究,借鉴分室沉积的器件质量级μc-Si材料的经验,选取合适的本征层和P种子层处理B污染的技术,在单室中制备出光电转换效率为6.23%(1 cm2)的单结μc-Si电池.     

温度对高速微晶硅薄膜沉积速率及其特性的影响

采用超高频(VHF)结合高压(HP)的技术路线,在较高SiH4浓度(SC)下实现了微晶硅(μc-Si:H)薄膜的高速沉积,考察了衬底温度在化学气相沉积(CVD)过程中对薄膜的生长速率以及光电特性的影响.结果表明:薄膜微结构特性随衬底温度变化是导致薄膜电学特性随衬底温度变化的根本原因;HP与低压条件下沉积的μc-Si:H薄膜的特性随温度变化的规律不同,在试验温度范围内,HP高速沉积的μc-Si:H薄膜生长速率不同于低压时随温度升高而下降的趋势,而是先增大后趋于平稳,晶化率随温度升高也不是单调增加,而是先增加后减小.     

衬底温度对微晶硅薄膜沉积与结构特征的影响

采用甚高频等离子体化学气相沉积(VHF-PECVD)技术在不同衬底温度条件下沉积了氢化微晶硅(μc—Si：H)薄膜,并通过光发射谱(OES)测量技术对沉积过程中硅烷(SiH4)等离子体进行了原位监测。结合对样品的沉积速率测量与结构表征,研究了衬底温度对薄膜沉积过程与结构特征的影响。实验结果表明：随着衬底温度的增加,μc—Si：H薄膜结晶体积分数与晶粒的平均尺寸单调增大,而沉积速率则呈现出先增后减的变化。对于当前的沉积系统,优化生长的衬底温度约为210℃,相应的μc-Si：H薄膜沉积速率为0．8nm／s,结晶体积分数与晶粒平均尺寸分别为60％和9nm。     

微晶硅薄膜制备中等离子体功率的调制作用

对甚高频等离子体增强化学气相沉积(VHF-PECVD)法制备氢化微晶硅(μc-Si:H)薄膜中等离子体功率的影响进行了研究.原位光发射谱(OES)监测表明,SiH4等离子体中特征发光峰ISiH、Ihα、Ihβ和IH/ISiH均随等离子体激发功率的增加而增大,并且变化趋势因功率区间的不同而异.由厚度与Raman光谱测量可知,随着等离子体功率的增加,μc-Si:H薄膜的平均晶粒尺寸单调减小,而沉积速率与结晶体积分数则呈现出先增后减的变化,等离子体功率对薄膜的沉积速率与结构特征具有"调制作用".光暗电导率测量进一步得到,μc-Si:H薄膜的电导随等离子体功率增大而减小,暗电导率的变化与之相反,材料的光敏特性在较高功率条件下激剧恶化.研究结果表明,当前的沉积条件下,等离子体功率的优化值界于35～40 W间.     

流量对高速沉积的微晶硅电池性能的影响

采用超高频等离子体增强化学气相沉积(VHF-PECVD)技术研究微晶硅(μc-Si)薄膜的高速沉积过程发现:分别采用100和500 sccm流量制备本征μc-Si材料,将其应用在μc-Si电池i层,电池的电流-电压(I-V)特性有明显的差异.通过微区Raman、原子力显微镜(AFM)和X射线衍射(XRD)测试发现:尽管μc-Si薄膜的晶化率相似,但是小流量情况下制备的薄膜具有较厚的非晶孵化层,晶粒尺寸不一;大流量下制备的材料沿生长方向的纵向均匀性相对较好,晶粒尺寸较小、分布均匀,而且具有〈220〉晶相峰强度高于〈111〉和〈311〉晶相峰强度的特点.因此得出:在高压高速沉积μc-Si薄膜过程中,反应气体流量对μc-Si的纵向结构有很大影响,选择适合的反应气流量能够调节适宜的气体滞留时间,从而减小薄膜的纵向不均匀性.     

器件质量级微晶硅薄膜光稳定性研究

利用射频等离子体增强化学气相沉积（RFPECVD）技术,通过改变SiH4浓度制备了一系列不同晶化率（Xc）的本征Si薄膜材料。通过测量其Raman谱和光、暗电导率（σph、σd）研究了工艺变化对材料结构的影响及材料光电特性同微观结构的关系,然后对样品进行老化实验,测量其光照前后的吸收系数α及量子效率、迁移率和寿命的乘积nμτ。分析其光照前后光电性能的变化规律结果表明,相变域附近的微晶硅（μc-Si：H）薄膜材料适合制备μc-Si2H太阳电池;结合退火实验的结果发现,μc-Si：H材料中的非晶成分是导致微晶材料光电特性衰退的主要原因。     

PET塑料衬底非晶/微晶硅叠层太阳电池研究

采用射频等离子体增强化学气相沉积(RF-PECVD)技术,在125℃的低温条件下,沉积了一系列不同厚度的本征微晶硅(μc-Si)薄膜。对材料的光电特性和结构特性的测试结果表明,低温条件下制备的μc-Si薄膜具有较厚的非晶孵化层,并且纵向结构演变较为明显。采用梯度H稀释技术,在沉积过程中不断降低H稀释度,改善了μc-Si薄膜的纵向均匀性。将此技术应用于非晶硅(a-Si)/μc-Si叠层电池的μc-Si底电池,在聚对苯二甲酸乙二醇酯(PET)塑料衬底上制备出初始效率达到6.0%的a-Si/μc-Si叠层电池。     

高速沉积μc-Si:H薄膜生长机制及其微结构的研究

采用高压高功率的超高频等离子体增强化学气相沉积(VHF-PECVD)技术,在腐蚀后的7059玻璃、低晶化和高晶化的微晶硅(μc-Si:H)p型材料3种衬底上,通过改变沉积时间的方法,高速(沉积速率约为1 nm/s)沉积了不同厚度的μc-Si:H薄膜材料.测试其表面形貌及晶化率,比较了不同衬底上高速生长的μc-Si:H薄膜生长机制及微结构的差异,最后得到适于高速沉积pin μc-Si:H太阳电池的μc-Si:H p型材料应具备的条件.     

弱硼掺杂补偿对氢化微晶硅薄膜制备与特性的影响

研究了弱硼掺杂补偿对甚高频等离子体增强化学气相沉积方法生长氢化微晶硅薄膜(μc-Si:H)及材料特性的影响.实验发现,随着弱硼补偿剂量的增大,μc-Si:H薄膜的沉积速率先减小后增加,变化范围约为0.7～0.8nm/s.相比较而言,材料的结晶度以及晶粒的平均颗粒尺寸则呈现出先增后减的变化,且变化的幅度较大,当弱硼补偿剂量大于2.5ppm时,过度的弱硼补偿将导致μc-Si:H薄膜的结晶状况恶化.此外,光敏性、暗电导及电导激活能的测量结果进一步表明,弱硼补偿显著影响μc-Si:H薄膜的光电特性,弱硼补偿剂量为2.5ppm左右时,材料的光电特性最为理想.因此,优化弱硼补偿剂量是获得器件级质量μc-Si:H材料的有效途径.     

1nm/s高速率微晶硅薄膜的制备及其在太阳能电池中的应用

采用甚高频等离子体增强化学气相沉积技术,在相对较高气压和较高功率条件下,制备了不同硅烷浓度的微晶硅材料.材料沉积速率随硅烷浓度的增加而增大,通过对材料的电学特性和结构特性的分析得知:获得了沉积速率超过1 nm/s高速率器件质量级微晶硅薄膜,并且也初步获得了效率达6.3%的高沉积速率微晶硅太阳电池.     

VHF-PECVD制备不同衬底温度微晶硅薄膜结构研究

采用微区拉曼散射、傅立叶变换红外吸收和光热偏转谱对VHF-PECVD制备的不同衬底温度硅薄膜进行了微结构分析.结果表明:随衬底温度的升高,薄膜逐渐由非晶向微晶过渡,晶化率(Xc)逐渐增大,样品中的氢含量逐渐降低.在200~250℃条件下制备的微晶硅薄膜具有低的缺陷密度.通过优化工艺条件制备出了效率达7.1%的单结微晶硅太阳电池,电池厚度仅为1.2μm,且没有ZnO背反射电极.     

掺杂室沉积本征微晶硅材料及其在太阳能电池中的应用

在掺杂P室采用甚高频等离子体增强化学气相沉积（VHF—PECVD）技术,制备了不同硅烷浓度条件下的本征微晶硅薄膜．对薄膜电学特性和结构特性的测试结果分析表明：随硅烷浓度的增加,材料的光敏性先略微降低后提高,而晶化率的变化趋势与之相反;X射线衍射（xRD）测试表明材料具有（220）择优晶向．在P腔室中用VHF—PECVD方法制备单结微晶硅太阳能电池的i层和p层,其光电转换效率为4．7％,非晶硅／微晶硅叠层电池（底电池的p层和i层在P室沉积）的效率达8．5％．     

Effects of modulation frequency on the structure and electrical characteristics of μc-Si:H films prepared by pulsed VHF-PECVD

Modulation frequency and pulse duty cycle are two key parameters of pulsed VHF-PECVD technology. An experimental study on the mierocrystalline silicon materials prepared by pulsed VHF-PECVD technology in high deposition rate is presented. And combining the diagnosis of plasma process with optical emission spectroscopy （OES）, the dependence of microstructure and electrical properties of thin films on the pulse modulation frequency is discussed in detail.     

Improved micromorph solar cells by means of mixed‐phase n‐doped silicon oxide layers

A good light trapping scheme is necessary to improve the performance of amorphous/microcrystalline silicon tandem cells. This is generally achieved by using a highly reflective transparent conducting oxide/metal back contact plus an intermediate reflector between the component cells. In this work, the use of doped silicon oxide as alternative n‐layer in micromorph solar cells is proposed as a means to obtain high current values using a simple Ag back contact and no extra reflector between the component cells n‐doped silicon oxide layers with a wide range of optical and electrical properties have been prepared. The influence of different deposition regimes on the material properties has been studied. The main findings are the following: (i) when carbon dioxide is added to the gas mixture, sufficiently high hydrogen dilution is necessary to widen the transition region from highly conductive microcrystalline‐like films to amorphous material characterized by low electrical conductivity; (ii) lower refractive index values are found with lower deposition pressure. Optimal n‐doped silicon oxide layers have been used in both component cells of micromorph devices, adopting a simple Ag back contact. Higher current values for both cells are obtained in comparison with the values obtained using standard n‐doped microcrystalline silicon, whereas similar values of fill factor and open circuit voltage are measured. The current enhancement is particularly evident for the bottom cell, as revealed by the increased spectral response in the red/infrared region. The results prove the high potential of n‐doped silicon oxide as ideal reflector for thin‐film silicon solar cells. Copyright © 2011 John Wiley & Sons, Ltd.     

本征微晶硅薄膜的结构演变及其对太阳电池光伏性能的影响

采用高压射频等离子体增强化学气相沉积(RF-PECVD)方法制备本征硅薄膜和n-i-P结构太阳电池,研究了氢稀释率对本征硅薄膜的电学特性和结构特性的影响.采用光发射谱(OES)和喇曼(Raman)散射光谱研究了处于过渡区的本征硅薄膜的纵向结构演变过程.结果表明:光发射谱和喇曼散射光谱可以作为研究硅薄膜的纵向结构演变有效手段.随着氢稀释率的增加,硅薄膜从非晶相向微晶相过渡时,其纵向结构的改变会严重影响硅薄膜太阳电池的光伏性能.     

Use of seed layers for structure,optical, and electronic transport measurements on microcrystalline silicon on glass

A detailed structural analysis is provided by which the benefits of thin undoped ‘seed layers’ for the preparation of microcrystalline silicon on glass for material characterization are demonstrated. Raman spectroscopy and photothermal deflection spectroscopy (PDS) results reveal that ‘seed layers’ are not only effective for the growth of structurally homogenous films and for an extension of the range of deposition parameters in which highly crystalline material is grown, but also allow for preparing material on glass with properties very close to that of functional layers in thin film solar cells. Films which have successfully been tailored in this way are characterized with respect to electrical conductivity and optical absorption. Regarding conductivity, hydrogenated microcrystalline silicon material grown on a ‘seed layer’ exhibits a structure‐dependent behaviour which is very similar to that observed for material grown on bare glass. Regarding optical absorption spectra, residual interference fringes, which indicate structural non‐uniformities, can be successfully removed by means of ‘seed layers’. As a result, more information is obtainable from PDS, and the data gained in this way are in good agreement with Raman spectroscopy results. Copyright © 2011 John Wiley & Sons, Ltd.     

A New View of Microcrystalline Silicon: The Role of Plasma Processing in Achieving a Dense and Stable Absorber Material for Photovoltaic Applications

To further lower production costs and increase conversion efficiency of thin‐film silicon solar modules, challenges are the deposition of high‐quality microcrystalline silicon (μc‐Si:H) at an increased rate and on textured substrates that guarantee efficient light trapping. A qualitative model that explains how plasma processes act on the properties of μc‐Si:H and on the related solar cell performance is presented, evidencing the growth of two different material phases. The first phase, which gives signature for bulk defect density, can be obtained at high quality over a wide range of plasma process parameters and dominates cell performance on flat substrates. The second phase, which consists of nanoporous 2D regions, typically appears when the material is grown on substrates with inappropriate roughness, and alters or even dominates the electrical performance of the device. The formation of this second material phase is shown to be highly sensitive to deposition conditions and substrate geometry, especially at high deposition rates. This porous material phase is more prone to the incorporation of contaminants present in the plasma during film deposition and is reported to lead to solar cells with instabilities with respect to humidity exposure and post‐deposition oxidation. It is demonstrated how defective zones influence can be mitigated by the choice of suitable plasma processes and silicon sub‐oxide doped layers, for reaching high efficiency stable thin film silicon solar cells.