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阳光转化为电能：使用 1 太阳（平板形式）的硅太阳能电池和与聚光光学器件和跟踪系统结合使用的基于 III-V 族的多结电池。作为单结器件，硅电池的效率理论上限制在约 30%，但已达到约 25% 的实际限制。多结技术可能会在本十年内生产出浓度超过 50% 的电池效率；然而，用于 1-sun 应用的电池成本非常高。因此，硅电池技术的当务之急是降低成本，同时保持高效率。还有一个巨大的机会来开发多结电池技术，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，我们在这两个方向都取得了重大进展，继续研究努力可能会取得突破。 由于硅材料占电池成本的很大一部分，因此有很大的动力使用比目前约 180 µm 更薄的晶圆。然而，当今使用的硅晶片有双重用途。它为晶圆处理提供机械支撑，并且由于硅是一种较差的光学吸收体，因此需要其厚度才能实现最佳吸收。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，同时几乎消除材料成本。我们制造了 10 µm 厚的单晶硅膜太阳能电池，采用简单的光捕获方法，器件效率约为 10%。设计（通过数值模拟）、制造（通过低成本方法）、光学表征（验证设计）和更先进的光捕获策略的实施预计将产生厚度在 2-10 µm 范围内且效率超过 20% 的电池。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，每个子电池都设计用于从太阳光谱的一部分中最佳地捕获能量。 Ge 衬底的另一种方法是使用更便宜的 Si 衬底作为底部电池，利用硅电池技术的巨大基础设施。这种方法有两个障碍，首先，硅电池成为三结器件的限流电池，损害了顶部电池的能量转换；其次，尚未证明可以在硅衬底上生长足够高质量的材料。在我们最近的工作中，我们找到了这两个问题的解决方案，发明了面积电流匹配技术以将硅电池的电流与顶部电池相匹配，并开发了晶圆键合方法，以混合集成方法将单独优化的硅和III-V电池连接起来，生产出效率为25.8%的电池，这是硅基多结太阳能电池的世界纪录。我们相信通过这种方法可以实现电池效率超过30%。 然而，我们的长期目标是制造足够便宜的多结电池，用于 1 太阳应用，同时超过传统 1 太阳电池目前的限制。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，并通过晶圆键合和面积电流匹配将它们与硅底部电池结合起来。这种雄心勃勃的方法将具有变革性，为电池提供比目前可用的效率更高的电池，适合广泛部署。