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: 2015
• 资助国家: 加拿大
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=587388
• 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力。 SI太阳能电池在1-Sun（平面格式）和III-V基于III-V的多式单元中使用，并与浓度光学和跟踪系统结合使用。作为单个连接设备，SI细胞理论上的效率约为30％，其实际限制约为25％。在本十年的浓度下，多肺技术可能会产生超过50％效率的细胞。但是，禁止将细胞成本高于1-Sun应用。因此，在SI细胞技术中，最重要的是降低成本，同时保持高效率。还有一个巨大的机会来开发一种多功能细胞技术，该技术具有足够的成本效益，可以在1-SUN应用中实施。根据最近的研究结果，我们在这两个方向上都取得了重大进展，并且持续的研究工作可能会产生突破。 由于SI材料是细胞成本的很大一部分，因此使用比电流〜180 µm的稀波有很大的动机。但是，当今使用的SI Wawver具有双重目的。它为摇动处理提供了机械支持，并且由于SI是一种较差的光学吸收剂，其厚度是最佳吸收所需的。但是，使用先进的光捕获策略可以将光路长度至少增加50倍，从而实现与常规厚细胞相当的效率，同时实际上消除了材料成本。我们已经制造了10 µm厚的单晶Si-Membrane太阳能电池，并结合了简单的光捕获方法，产生了〜10％的设备效率。设计（通过数值模拟），制造（通过低成本方法），光学表征（佐证设计）和更先进的光捕获策略的实施，预计将产生厚度在2-10 µm范围内的细胞，效率超过20％。具有先进设计的薄Si细胞有可能在保持效率的同时大大降低成本。 在多期太阳能电池中，每个子细胞均设计为从太阳能光谱的一部分中最佳捕获能量。 GE底物的另一种方法是为底部细胞使用较便宜的Si基板，利用SI细胞技术的巨大基础设施。这种方法有两种障碍，首先，SI细胞成为三重连接装置的当前限制单元，从而损害了顶部细胞的能量转换，其次，没有证明可以具有足够高质量的SI基板上的材料。在我们最近的工作中，我们发现了解决这两个问题的解决方案，并发明了Areal电流匹配，以使Si细胞的电流与顶部细胞与顶部细胞的电流以及晶状键合法的发展，以在混合整合方法中分别优化的SI和III-V细胞，以25.8％的效率产生SI基于SI基于SI的多期多个单元的世界记录。我们认为，使用这种方法可以实现效率超过30％的细胞。 但是，我们的长期目标是制造多功的单元，这些细胞足够便宜地用于1-Sun应用，同时超过了常规1-SUN细胞的当前限制。我们建议使用比当前使用的MOCVD工艺要便宜得多的工艺来制作高质量的III-V太阳能电池，并通过晶圆粘结和面积电流匹配将它们与SI底部细胞结合在一起。这种雄心勃勃的方法将具有变革性，为细胞提供的效率明显高于当前可用的效率，适合于宽度部署。