Lower Cost and Higher Efficiency Solar Cells for 1-sun Applications

适用于 1 太阳应用的成本更低、效率更高的太阳能电池

• 批准号: RGPIN-2014-03736
• 负责人: Kleiman, Rafael
• 金额: $ 3.06万
• 依托单位: McMaster University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=610620
• 关键词: Lower; Cost; Higher; Efficiency; Solar

There are currently two broad technologies used for converting sunlight to electricity; Si solar cells used at 1-sun (in a flat panel format) and III-V based multijunction cells used in conjunction with concentration optics and tracking systems. As single junction devices, Si cells are limited theoretically to ~30% efficiency and have reached their practical limit of ~25%. Multijunction technology is likely to produce cells exceeding 50% efficiency under concentration this decade; however the cell costs are prohibitively high to be used in 1-sun applications. Therefore, the greatest imperative in Si cell technology is to reduce the cost, while maintaining high efficiency. There is also a tremendous opportunity to develop a multijunction cell technology that is sufficiently cost effective to be implemented in 1-sun applications. Based on recent research results, we have made significant progress in both directions and continued research efforts are likely to yield breakthroughs. Since the Si material is a significant fraction of the cell cost, there is substantial incentive to use thinner wafers than the current ~180 µm. However, the Si wafer in use today serves a dual purpose. It provides mechanical support for wafer handling and since Si is a poor optical absorber its thickness is required for optimal absorption. However, the optical path length can be increased by at least a factor of 50 using advanced light trapping strategies, with the potential to achieve efficiencies comparable to conventional thick cells, while virtually eliminating the material cost. We have fabricated 10 µm thick single-crystal Si-membrane solar cells, incorporating simple light trapping methods, yielding a device efficiency of ~10%. The design (via numerical simulation), fabrication (via low cost methods), optical characterization (corroborating designs) and implementation of more advanced light trapping strategies are expected to yield cells with thicknesses in the range of 2-10 µm and efficiencies exceeding 20%. Thin Si cells with advanced designs have the potential to dramatically reduce cost, while maintaining efficiency. In multijunction solar cells, each sub-cell is designed to optimally capture energy from a portion of the solar spectrum. An alternate approach to Ge substrates is to use much less expensive Si substrates for the bottom cell, leveraging the tremendous infrastructure of Si cell technology. There are two impediments with this approach, firstly that the Si cell becomes the current limiting cell for the triple junction device, compromising the energy conversion from the top cells and secondly that it has not proven possible to grow materials on Si substrates with sufficiently high quality. In our recent work, we have found solutions to both problems, with the invention of areal current matching to match the current of the Si cell to the top cells and the development of wafer bonding methods to join separately optimized Si and III-V cells in a hybrid integration approach, yielding cells with 25.8% efficiency, a world record for a Si-based multijunction solar cell. We believe that cells with efficiency in excess of 30% can be achieved with this method. However, our long term objective is to make multijunction cells that are sufficiently inexpensive for use in 1-sun applications, while exceeding the present limits of conventional 1-sun cells. We propose to make high quality III-V solar cells using a much less expensive process than the MOCVD process currently used and combine them with Si bottom cells via wafer bonding and areal current matching. This ambitious approach would be transformative, providing cells with significantly higher efficiencies than currently available, suitable for widespread deployment.

目前有两种广泛的技术用于将太阳光转换为电能：用于1个太阳的硅太阳能电池(平板形式)，以及与聚光光学和跟踪系统结合使用的基于III-V的多结电池。作为单结器件，硅电池的效率在理论上被限制在~30%，而在实际应用中已经达到了25%的极限。多结技术很可能在本十年内生产出效率超过50%的电池；然而，用于一太阳应用的电池成本高得令人望而却步。因此，硅电池技术的最大当务之急是在保持高效率的同时降低成本。也有一个巨大的机会来开发一种多结电池技术，该技术具有足够的成本效益，可以在1-SUN应用中实施。根据最近的研究成果，我们在两个方向上都取得了重大进展，继续研究努力很可能会取得突破。 由于硅材料占电池成本的很大一部分，因此有很大的动机使用比目前~180微米更薄的晶片。然而，今天使用的硅晶片具有双重用途。它为晶片搬运提供了机械支持，由于硅是一种很差的光吸收材料，其厚度是实现最佳吸收所必需的。然而，使用先进的光捕获策略，光路长度可以增加至少50倍，有可能实现与传统厚电池相当的效率，同时几乎消除了材料成本。我们制作了10微米厚的单晶硅薄膜太阳电池，结合简单的光捕获方法，产生了约10%的器件效率。设计(通过数值模拟)、制造(通过低成本方法)、光学表征(确证设计)和实施更先进的光捕获策略预计将产生厚度在2-10微米范围内的电池，效率超过20%。具有先进设计的薄硅电池有可能在保持效率的同时大幅降低成本。 在多结太阳能电池中，每个子电池被设计为最佳地从太阳光谱的一部分捕获能量。使用Ge衬底的另一种方法是使用成本低得多的Si衬底作为底部单元，利用硅单元技术的巨大基础设施。这种方法有两个障碍，一是硅单元成为三结器件的限流单元，影响了顶层单元的能量转换；二是还没有证明在硅衬底上生长足够高质量的材料是可能的。在我们最近的工作中，我们已经找到了这两个问题的解决方案，发明了面积电流匹配以匹配硅电池与顶部电池的电流，并开发了晶片键合方法以混合集成方法连接单独优化的硅和III-V电池，产生了效率为25.8%的电池，这是硅基多结太阳能电池的世界纪录。我们相信，用这种方法可以获得效率超过30%的电池。 然而，我们的长期目标是制造足够便宜的多结电池，用于1-SUN应用，同时超过目前传统1-SUN电池的限制。我们建议使用比目前使用的MOCVD工艺便宜得多的工艺来制造高质量的III-V太阳能电池，并通过晶片键合和面电流匹配将它们与硅底电池结合起来。这一雄心勃勃的方法将是变革性的，提供比目前可用的效率高得多的电池，适合广泛部署。