SBIR Phase I: Dry Epitaxial Lift-off for High Efficiency Solar Cells

这个小企业创新研究第一阶段项目开发了一种方法，将外延生长的高效率（30%）三结III-V型太阳能电池从锗或砷化镓晶圆上提升到聚酰亚胺衬底上。高热膨胀系数（CTE）聚酰亚胺晶圆在冷却至室温以下时，由于热膨胀系数之间的不匹配，在外接层/晶圆界面处产生平行于表面的裂纹。升空只需几分之一秒，而且不需要昂贵的离子注入或缓慢的化学蚀刻牺牲层。外延层附着在具有25至100微米厚度的低成本柔性聚酰亚胺衬底上，该衬底作为太阳能电池的永久载体。倒置的和非倒置的细胞都可以用这种技术取出来。基材可以重复使用以生长另一层外延层，并重复此循环。对于这些器件，衬底材料的成本约为成品电池成本的40%。这一过程将节省原材料、研磨和蚀刻成本，最多可节省电池成本的30%。该项目更广泛的影响/商业潜力将是开发一种方法，将外延生长的器件层从半导体晶圆转移到廉价的聚合物衬底上，以创建高性能的柔性电路。这项技术的应用超出了光伏（PV）。当这一过程被整合到现有供应商的制造流程中时，太空级和地面级的高效光伏电池和模块可以变得更轻、更灵活、更便宜。此外，当变薄的电池转移到金属衬底时，减少的厚度提高了地面聚光光伏系统的性能。一旦这种方法得到证实，我们将利用我们与主要高效太阳能电池制造商的关系，就该技术的应用许可进行谈判。

This Small Business Innovation Research Phase I project develops a method of lifting-off an epitaxially grown high-efficiency ( 30%) triple-junction III-V solar cell from a Ge or GaAs wafer onto a polyimide substrate. A high-coefficient of thermal expansion (CTE) polyimide wafer is used to induce a crack that propagates parallel to the surface at the epi/wafer interface, due to the mismatch between the coefficients of thermal expansion, as the wafer is cooled down below room temperature. The lift-off happens in a fraction of a second and no expensive ion implantation or slow chemical etching of a sacrificial layer is needed. The epi-layer is attached to a low-cost flexible polyimide substrate having a thickness between 25 and 100 microns which serves as the permanent carrier of the solar cell. Inverted and non-inverted cells can be lifted off using this technique. The base substrate can be reused to grow another epi-layer and the cycle repeated. For these devices, the cost of substrate materials is about 40% of the cost of the finished cell. This process will result in savings of raw materials and grinding and etching costs, up to a total savings of 30% of the cost of the cell. The broader impact/commercial potential of this project will be to develop a method to transfer epitaxially-grown device layers from semiconductor wafers to inexpensive polymeric substrates to create high-performance flexible circuits. The application of this technology goes beyond photovoltaics (PV). Space-grade as well as terrestrial high-efficiency PV cells and modules can be made lighter, flexible, and less expensive when this process is integrated into the manufacturing sequence of established suppliers. Additionally, when the thinned cell is transferred to a metallic substrate, the reduced thickness improves performance of terrestrial concentrating PV systems. Once this method is demonstrated, we will leverage our relationships with major high-efficiency solar cell manufacturers to negotiate licensing of the technology for their applications.