Role of Small Angle Grain Boundaries in CdTe Solar Cell Performance

摘要标题：晶界在碲化镉太阳能电池性能中的作用非技术描述：太阳能因其可再生、低环境影响和潜在的低成本而引起人们的兴趣，以解决日益增长的全球能源需求。在薄膜太阳能技术中，入射光被吸收在器件的微米薄半导体有源层中，在支撑基板上堆叠其他薄膜层以完成器件。碲化镉（CdTe）太阳能电池是目前价格最低的薄膜技术，工业化量产，与传统的不可再生电力相比具有成本竞争力。这项技术的成功部分依赖于大规模工艺生产高电子质量的材料。CdTe活性层的工业沉积时间为~ 30秒。然而，为了提高材料的电子质量和器件性能，需要额外的CdCl2化学处理，这将增加约30分钟的处理时间。碲化镉薄膜可以被认为是一种由有序晶粒和晶界材料组成的复合材料，两者都具有影响器件性能的特性。我们将研究晶界结构对CdTe电子性能的影响，最终目的是确定沉积结构，从而减少或消除耗时的CdCl2过程，从而降低成本。通过结合先进的材料沉积来控制CdTe的晶界特性，这些晶界结构的理论建模，以及全CdTe太阳能电池的制造和加工，将揭示CdTe层特性与太阳能电池器件性能之间的联系。这项工作对国家利益的能源和其他技术应用有影响。pi和博士候选人将参与外展活动，为当地K-12学生和教师、公众和行业的教育做出贡献。技术描述：CdCl2处理通过促进晶体晶粒生长，减少缺陷的影响，并通过用Cl取代~50%的晶界Te来改变晶界化学来修饰CdTe。我们将研究晶界结构对CdTe电子性能的影响，最终目的是确定沉积态微结构，从而减少或消除耗时的CdCl2过程，从而降低成本。CdTe薄膜将以相对于沉积通量的斜角法向溅射沉积，制备出晶粒取向可控、晶界角小的材料。现场实时光谱椭偏仪将用于监测、研究和控制这些薄膜的生长演变。密度泛函理论计算将执行，以确定晶体取向和晶界的能量学。可控取向CdTe将被整合到单结太阳能电池中，作为正常入射溅射或近空间升华CdTe的全部或部分替代层。对于定向可控的CdTe器件，将确定CdCl2处理和处理时间对性能的影响。晶粒结构和器件性能之间的基本联系将被评估，晶粒边界结构能够减少CdCl2的加工时间

Abstract Title: Role of Grain Boundaries in CdTe Solar Cell Performance Non-Technical Description: Solar power is of interest to address the growing global energy demand as it is renewable, low environmental impact, and potentially low cost. Within thin film solar technology, power is generated from incident light absorbed in a microns-thin semiconducting active layer of the device, among a stack of other thin film layers on a supportive substrate to complete the device. Cadmium telluride (CdTe) solar cells are the current lowest price thin film technology, industrially mass-produced, and cost-competitive with traditional non-renewable electric power. Part of the success of this technology relies on producing high electronic quality material in large-scale processes. Industrial deposition time of the CdTe active layer is ~ 30 seconds. However, additional CdCl2 chemical treatment, required to improve material electronic quality and device performance, adds ~ 30 minutes processing time. CdTe films can be considered a composite of well-ordered crystalline grains and grain boundary materials with properties of both impacting device performance. The role grain boundary structure plays on the electronic properties of CdTe will be studied with the ultimate intention of identifying as-deposited structures that enable reduction or elimination of the time-consuming CdCl2 process to lower cost. By combining advanced material deposition to control CdTe grain boundary characteristics, theoretical modeling of these grain boundary structures, and fabrication and processing of full CdTe solar cells links between CdTe layer characteristics and solar cell device performance will be uncovered. The work has implications for energy and other technological applications of national interest. The PIs and the PhD candidates will engage in outreach activities that will contribute to the education of local K-12 students and teachers, the general public, and industry. Technical Description: CdCl2 treatment modifies CdTe by promoting crystalline grain growth, reducing the impact of defects, and changing grain boundary chemistry by replacing ~50% of the boundary Te with Cl. The role grain boundary structure plays on the electronic properties of CdTe will be studied with the ultimate intention of identifying as-deposited microstructures that enable reduction or elimination of the time-consuming CdCl2 process to lower cost. CdTe films will be sputter deposited with the substrate normal at an oblique angle relative to the deposition flux, producing material with controllable grain orientation and small angle grain boundaries. In situ real time spectroscopic ellipsometry will be used to monitor, study, and control the growth evolution of these films. Density functional theory calculations will be performed to identify energetics of crystallite orientations and grain boundaries. Controlled orientation CdTe will be incorporated into single junction solar cells as either full or partial replacement layers for normal incidence sputtered or close space sublimated CdTe. Impact of CdCl2 treatment and processing time on performance will be identified for devices with controlled orientation CdTe. Fundamental connections between grain structure and device performance will be evaluated, with grain boundary structure enabling reduced CdCl2 processing times identified