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首页> 外文学位 >Understanding and development of dielectric passivated high efficiency silicon solar cells using spin-on solutions.
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Understanding and development of dielectric passivated high efficiency silicon solar cells using spin-on solutions.

机译：使用旋转解决方案来理解和开发介电钝化的高效硅太阳能电池。

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This thesis successfully demonstrated the use of spin-on solutions in the fabrication of high efficiency cells. A diffusion process was designed using in-house developed Phosphoric acid dopant solutions and optimized to produce emitters with high surface concentration and optimal emitter profile. Optimal gas-flow was identified as an important factor for uniform emitter formation. In addition, the process was modified to include a short pre-oxidation step after wafer loading that resulted in emitters with higher uniformity of diffusion and lower emitter saturation current density (< 100 fA/cm 2). This modified diffusion process was also more reproducible as it was insensitive to ambient humidity, unlike earlier processes using spin-on dopants. This emitter was first used to fabricate full Al BSF conventional cells (4 cm2) with screen printed contacts, which led to cell efficiencies > 19.0%. This represents the highest efficiency for a screen printed full BSF cells. Further analysis and characterization showed that a high quality in-situ oxide passivation of the emitter along with very good screen printed contacts contributed to this high efficiency.;This high quality emitter was then used with a spin-on dielectric for the fabrication of a local BSF cell structure in which more than 95% of the rear surface was passivated by a dielectric with local contacts and back- surface field over the remaining area. Fabrication of such a device would generally require multiple high temperature steps. A simple streamlined process was designed that produced a diffused and passivated device in just a single high temperature step. Phosphoric acid based spin-on dopant sources were used for emitter diffusion and a spin-on dielectric was used for rear passivation. This process, called Delta-STAR, resulted in diffusion of phosphorous only on the emitter side of the wafe. An in-situ oxidation step was also performed immediately after diffusion, which resulted in improved emitter passivation and anneal of the rear passivating dielectric.;A screen-printed etching process was used first to define the local vias through the dielectric but was found to be non-uniform, resulting in inconsistent solar cell performance. However, it did produce 20% efficient cells in the best case. This non-uniformities in the etching process resulted in formation of parasitic current paths between the rear contacts and inverted silicon underneath the rear dielectric. An alternate processing route was required to ensure improved reproducibility of this technology and insensitivity to substrate thickness, dielectric thickness and surface quality. Several laser candidates were investigated in this work for replacing the screen-printed method of via definition. High efficiency local BSF cells were fabricated using a UV laser for selective rear dielectric removal. The performance of the cells fabricated by UV laser ablation and screen-printed etching paste was very similar. Observation of the laser ablated vias under an optical microscope and SEM indicated that the vias formed using lasers had some amount of surface damage, but compensated by the formation of a good uniform BSF. Further cell characterization and analysis indicated that the overall quality of the rear passivation was maintained, which was also supported by SEM analysis and PC1D modeling.;To improve the manufacturability of these local BSF devices, they had to be fabricated on more inexpensive commercial substrates. Modeling was performed to understand the impact of substrate thickness and bulk lifetime on local BSF cell efficiency. Since the development work involved polished FZ wafers, first the effect of surface finish on these devices was investigated. Surface roughness was tailored using KOH solution based treatments. Local BSF cells fabricated on double side textured wafers failed and it was found that reduced surface roughness was very critical for rear passivation and cell performance. KOH planarized rear surface with an RMS surface roughness of ∼0.75 microm was found to be adequate and produced cell results comparable to those on polished FZ substrates. Using such surfaces cell efficiencies of ∼20% on 180 microm mCz and ∼19.4% on 150 microm Cz substrates were achieved. PC1D modeling was used to study the effect of substrate resistivity on LBSF cell efficiencies. Based on experimental data on surface passivation structures and device modeling, it was concluded that Cz substrate resistivities of 1-3 ohm.cm were optimum for local BSF solar cell performance after LID. (Abstract shortened by UMI.).
机译：本论文成功地证明了旋涂解决方案在高效电池制造中的应用。使用内部开发的磷酸掺杂剂溶液设计了扩散工艺，并对其进行了优化，以生产具有高表面浓度和最佳发射器轮廓的发射器。最佳的气流被确定为均匀的发射极形成的重要因素。另外，对该工艺进行了修改，使其包括在晶片加载后的短预氧化步骤，从而使发射极具有更高的扩散均匀性和更低的发射极饱和电流密度（<100 fA / cm 2）。与早期使用旋涂掺杂剂的工艺不同，这种改良的扩散工艺由于对环境湿度不敏感，因此具有更高的重现性。该发射极首先用于制造带有丝网印刷触点的完整Al BSF常规电池（4 cm2），从而导致电池效率> 19.0％。对于丝网印刷的完​​整BSF电池，这代表了最高效率。进一步的分析和表征表明，发射极的高质量原位氧化物钝化以及非常好的丝网印刷触点有助于实现这种高效率。然后将该高质量的发射极与旋涂电介质一起用于局部制造BSF电池结构，其中超过95％的背面被电介质钝化，该电介质在其余区域上具有局部接触和背面电场。这种装置的制造通常将需要多个高温步骤。设计了一种简单的流线型工艺，仅在一个高温步骤中即可产生扩散和钝化的器件。基于磷酸的旋涂掺杂剂源用于发射极扩散，旋涂电介质用于背面钝化。此过程称为Delta-STAR，导致磷仅在wafe的发射器侧扩散。扩散后还立即执行原位氧化步骤，从而改善了发射极钝化和后钝化电介质的退火。;首先使用丝网印刷蚀刻工艺来定义穿过电介质的局部过孔，但发现是不一致，导致太阳能电池性能不一致。但是，在最佳情况下，它确实能产生20％的有效电池。蚀刻过程中的这种不均匀性导致在后触点和后电介质下方的倒置硅之间形成寄生电流路径。需要一条替代的加工路线，以确保提高该技术的可重复性以及对基板厚度，电介质厚度和表面质量不敏感。在这项工作中研究了几种激光候选物，以代替通孔定义的丝网印刷方法。使用紫外激光制造高效率的局部BSF电池，以选择性去除背面电介质。通过紫外线激光烧蚀和丝网印刷的蚀刻膏制成的电池的性能非常相似。在光学显微镜和SEM下观察激光烧蚀的通孔，发现使用激光形成的通孔具有一定程度的表面损伤，但是可以通过形成良好的均匀BSF来补偿。进一步的电池表征和分析表明，后钝化的总体质量得以保持，这也得到了SEM分析和PC1D建模的支持。为了提高这些本地BSF器件的可制造性，必须在更便宜的商业基板上制造它们。进行建模以了解衬底厚度和本体寿命对局部BSF电池效率的影响。由于开发工作涉及抛光的FZ晶片，因此首先研究了表面光洁度对这些器件的影响。使用基于KOH溶液的处理来定制表面粗糙度。在双面纹理化晶片上制造的本地BSF电池失效，并且发现降低的表面粗糙度对于背面钝化和电池性能至关重要。发现RMS表面粗糙度约为0.75微米的KOH平坦化后表面是足够的，所产生的像元结果与抛光的FZ基板上的结果相当。使用这样的表面，在180 microm mCz上的电池效率约为20％，在150 microm Cz的基板上的电池效率约为19.4％。 PC1D建模用于研究底物电阻率对LBSF细胞效率的影响。根据表面钝化结构的实验数据和器件建模，可以得出结论，LID后1-3 ohm.cm的Cz衬底电阻率对于局部BSF太阳能电池性能是最佳的。 （摘要由UMI缩短。）。

著录项

  • 作者

    Ramanathan, Saptharishi.;

  • 作者单位

    Georgia Institute of Technology.;

  • 授予单位 Georgia Institute of Technology.;
  • 学科 Engineering Electronics and Electrical.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 204 p.
  • 总页数 204
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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