UNS: Collaborative Research: 30%-Efficient III-V/Silicon Tandem Solar Cells

PI: Minjoo Larry Lee / Zachary C. holman提案编号：1509687/ 1509864太阳代表着地球上最丰富的潜在可持续能源。目前，基于晶体硅材料的太阳能电池在太阳能发电市场占据主导地位，因为它们以最低的制造成本提供最高的太阳能转换效率。然而，为了加速太阳能在可再生电力市场的渗透，硅基太阳能电池的太阳能转换效率最终必须提高到24%以上的实际极限。该项目的目标是开发一种硅基太阳能电池，其中包含元素周期表中的III族和V族元素，这些元素分层排列，有可能将太阳能转换效率提高到30%。III-V/硅串联电池性能的基础科学将用于开发最终制造的最佳策略。作为该项目的教育活动的一部分，主要研究人员将积极参与外展计划，通过将太阳能研究作为参与退伍军人会议和西班牙裔专业工程师协会会议的技术和职业发展会议的平台，寻求扩大工程界代表性不足群体的参与。包含多个pn结的光伏器件是目前实现太阳能转换效率超过Shockley-Queisser单pn结极限的唯一途径，该极限限制了目前商业使用的晶体硅太阳能电池的理论性能。本研究的总体目标是通过控制III-V族元素在硅上的生长，对双端串联太阳能电池的性能有一个基本的了解。该制造策略以基础研究为指导，旨在优化材料和器件架构，实现30%的太阳能转换效率，超越单结晶体硅太阳能电池24%的实用极限。为此，选择用于研究的模型III-V组材料是GaAsP，因为它具有直接和可调的带隙，并且可以在GaP/Si模板上的透明，成分渐变的缓冲液上生长。串联装置的底部电池将基于非晶硅/晶体硅异质结太阳能电池，其中前部非晶硅层将被顶部电池生长的GaP模板层所取代。研究计划有三个目标。第一个目标是了解和控制GaAsP吸收器中螺纹位错的形成，并为顶部电池开发优化的窗口和后表面场层，这既可以增加GaAsP吸收器的透射率，又可以减少表面复合。第二个目标是了解和改进硅上GaP的钝化和电子在导带偏移上的输运。第三个目标是通过设计单面光捕获纹理和电介质/金属后反射器来最大化红外光在底层电池中的电流转换，然后调整III-V支撑层的厚度、掺杂密度和带隙，以形成亚电池之间的复合结并匹配它们的电流。研究成果将促进对多结太阳能电池性能的基础科学理解，同时开发制造策略，使可扩展的工业制造设备能够提供30%的太阳能转换效率。主要研究人员还将利用研究成果加强耶鲁大学和亚利桑那州立大学光伏课程的教学材料。

PI: Minjoo Larry Lee / Zachary C. HolmanProposal Number: 1509687/ 1509864The sun represents the most abundant potential source of sustainable energy on earth. Currently, solar cells based on crystalline silicon materials dominate the photovoltaics market for production of electricity from the sun because they offer the highest solar energy conversion efficiency at the lowest manufacturing cost. However, to accelerate the penetration of solar energy in the renewable electricity market, the solar energy conversion efficiency of silicon-based solar cells must ultimately increase beyond its practical limit of 24%. The goal of this project is develop a silicon-based solar cell which contains Group III and V elements from the Periodic Table, arranged in layers which have the potential to increase the solar energy conversion efficiency to 30%. The fundamental science underlying the performance of this the III-V/silicon tandem cell will be used to develop the best strategy for eventual manufacture. As part of the educational activities of this project, the principal investigators will be actively involved in an outreach program that seeks to broaden the participation of under-represented groups in engineering by using solar research as a platform for involvement in both technical and career-development sessions at Veterans meetings and the Society of Hispanic Professional Engineers conference.Photovoltaic devices that contain multiple p-n junctions are currently the only route to achieve solar energy conversion efficiencies that exceed the Shockley-Queisser single p-n junction limit that caps the theoretical performance of crystalline silicon solar cells currently in commercial use. The overall goal of this proposed research is to develop a fundamental understanding of two-terminal tandem solar cell performance through controlled growth of Group III-V elements on silicon. The fabrication strategy is guided by fundamental studies and is designed to optimize the material and device architecture to achieve 30% solar energy conversion efficiency, which is beyond the 24% practical limit of single-junction crystalline silicon solar cells. Towards this end, the model Group III-V material selected for study is GaAsP, since it has a direct and tunable bandgap, and can be grown on a transparent, compositionally graded buffer on a GaP/Si template. The bottom cell of the tandem device will be based on an amorphous silicon/crystalline silicon heterojunction solar cell, where the front amorphous silicon layers will be replaced with the GaP template layer upon which the top cell is grown. The research plan has three objectives. The first objective is to understand and control the formation of threading dislocations in the GaAsP absorber, and to develop optimized window and back-surface field layers for the top cell that will both increase transmission into the GaAsP absorber and reduce surface recombination. The second objective is to understand and improve the passivation of GaP on silicon and the transport of electrons across the conduction band offset. The third objective is to maximize the conversion of infrared light into current in the bottom cell by designing single-side light-trapping textures and dielectric/metal rear reflectors, and then tune the thicknesses, doping densities, and bandgaps of the III-V supporting layers to both form a recombination junction between the sub-cells and match their currents. The research outcomes will advance fundamental scientific understanding of multi-junction solar cell performance while developing fabrication strategies that will enable for scalable industrial manufacture of devices potentially capable of delivering 30% solar energy conversion efficiency. The principal investigators will also use the research outcomes to enhance instructional materials in photovoltaics course offerings at Yale University and Arizona State University.