Role of Small Angle Grain Boundaries in CdTe Solar Cell Performance

摘要标题：非技术描述：太阳能发电是解决全球能源需求增长的重要途径，因为它是可再生能源，对环境的影响小，成本低。 在薄膜太阳能技术中，功率是从器件的微米薄半导体有源层中吸收的入射光产生的，在支撑衬底上的其他薄膜层的堆叠中，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，工业化大规模生产，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取决于在大规模工艺中生产高电子质量材料。 CdTe活性层的工业沉积时间约为30秒。然而，额外的CdCl 2化学处理，需要提高材料的电子质量和器件性能，增加了约30分钟的处理时间。 CdTe膜可以被认为是具有影响器件性能的两种性质的有序晶粒和晶界材料的复合物。 将研究晶界结构对CdTe电子性质的作用，最终目的是确定沉积结构，从而减少或消除耗时的CdCl 2工艺以降低成本。通过结合先进的材料沉积来控制CdTe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层特性和太阳能电池器件性能之间的联系。这项工作对能源和其他国家感兴趣的技术应用有影响。PI和博士候选人将参与外联活动，这将有助于当地K-12学生和教师，公众和行业的教育。技术说明：CdCl 2处理通过促进晶粒生长、减少缺陷的影响以及通过用Cl取代~50%的边界Te来改变晶界化学来改性CdTe。 将研究晶界结构对CdTe电子特性的作用，最终目的是确定沉积的微结构，从而减少或消除耗时的CdCl 2工艺，以降低成本。 CdTe薄膜将被溅射沉积，其中衬底法线相对于沉积通量成斜角，从而产生具有可控晶粒取向和小角度晶界的材料。 原位真实的时间光谱椭圆偏振法将用于监测，研究和控制这些薄膜的生长演变。将进行密度泛函理论计算，以确定微晶取向和晶界的能量。 受控取向的CdTe将被并入单结太阳能电池中，作为正入射溅射或近空间升华的CdTe的全部或部分替代层。 将确定CdCl 2处理和处理时间对具有受控取向CdTe的器件性能的影响。 将评估晶粒结构和器件性能之间的基本联系，确定晶界结构能够减少CdCl 2处理时间

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