Collaborative Research: SusChEM: Air-stable, high-lifetime bismuth compounds as solar absorbers with perovskite-like band structures

合作研究：SusChEM：空气稳定、长寿命的铋化合物作为具有类钙钛矿能带结构的太阳能吸收剂

• 批准号: 1605495
• 负责人: Vladan Stevanovic
• 金额: $ 21.24万
• 依托单位: Colorado School of Mines
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1605495&HistoricalAwards=false
• 关键词: Collaborative; Research; SusChEM; Air; stable

The sun represents the most abundant potential source of sustainable energy on earth. Solar cells for producing electricity require materials that absorb the sun's energy and convert its photons to electrons, a process called photovoltaics. Recently, materials based on inorganic-organic halide perovskite materials have achieved promising solar energy power conversion efficiency approaching that of silicon solar cells, and can be made from earth-abundant elements using lower-cost, solution based fabrication methods. However, these perovskite materials contain lead, which is toxic, and they also degrade in the presence of moisture, which prevents their commercial use. To address these limitations, this project will develop new solar perovskite-like solar materials based on the element bismuth, which is both abundant and has low toxicity. This unexplored class of materials was identified through theoretical and computational techniques, and the research will use these theoretical insights to make and test the performance of this potentially exciting new class of materials for photovoltaic applications. The experimental findings, in combination with theoretical analysis, will feed back to the materials design criteria to help identify promising new materials for continued study. The educational activities associated with this project include laboratory internships offered in coordination with minority-serving organizations, hands-on learning modules, and the continued development of a semester-long solar photovoltaics course.Bismuth (Bi) compounds with perovskite-like band structures, including ternary bismuth halides and bismuth chalcohalides, are promising absorption materials for solar photovoltaic applications that go beyond conventional perovskite materials in three ways. First, their electronic structure and strong spin-orbit coupling can enable tolerance to intrinsic defects in a way that is similar to methylammonium lead iodide perovskite materials, but do not contain lead. Second, the bismuth cation has a large Born effective charge to provide high dielectric constants and screening of charged defects. And third, lead-free methylammonium bismuth iodide materials can be phase stable in the presence of water vapor due to the preferential formation of protective oxide layers. Given these potential advantages over lead-based organic metal halide perovskite materials, the overall goal of this research is to gain a fundamental understanding of the photovoltaic performance of bismuth-containing compounds as perovskite-like solar PV materials through theoretical and experimental investigation. Towards this end, the research has three objectives. The first objective is to investigate the importance of symmetry for favorable transport properties by investigating the alkali metal metathiobismuthites, one of the few classes of Bi-based materials that are not layered. The second objective is to develop models to determine the recombination processes and recombination rate in materials from time-resolved photoluminescence measurements. The third objective is to develop strategies for growing the new Bi-compounds with higher purity and correlate impurity content with minority carrier lifetime. Density functional theory will be used to determine the electronic structure, dielectric constant, and charge carrier effective masses. Experimental studies will establish the materials design criteria for efficient solar absorption, focusing on determining the role of intra-granular structural defects, molecular cations, and crystal symmetry on transport diffusion length, optical properties, and overall device performance. The diffusion length of the thin films will be obtained through time-resolved photoluminescence measurements as well as single photon and two-photon spectroscopy for depth-resolved lifetime measurements that decouple the effects of surface recombination.

太阳是地球上最丰富的可持续能源的潜在来源。 用于发电的太阳能电池需要吸收太阳能并将其光子转化为电子的材料，这一过程称为光电子学。 最近，基于无机-有机卤化物钙钛矿材料的材料已经实现了接近硅太阳能电池的有前景的太阳能功率转换效率，并且可以使用低成本的基于溶液的制造方法由地球丰富的元素制成。 然而，这些钙钛矿材料含有有毒的铅，并且它们在水分存在下也会降解，这阻碍了它们的商业用途。 为了解决这些局限性，该项目将开发基于元素铋的新型太阳能钙钛矿太阳能材料，这种材料既丰富又具有低毒性。 这类未经探索的材料是通过理论和计算技术确定的，研究将使用这些理论见解来制造和测试这类潜在的令人兴奋的新材料的性能，用于光伏应用。 实验结果与理论分析相结合，将反馈到材料设计标准，以帮助确定有前途的新材料，以继续研究。 与这一项目有关的教育活动包括与少数群体服务组织协调提供的实验室实习、动手学习模块以及继续开发一个学期的太阳能光电学课程。具有类钙钛矿能带结构的铋（Bi）化合物，包括三元卤化铋和硫代卤化铋，是有前途的太阳能光伏应用吸收材料，超越传统的钙钛矿材料在三个方面。 首先，它们的电子结构和强自旋轨道耦合可以以类似于甲基铵碘化铅钙钛矿材料的方式实现对本征缺陷的耐受性，但不含铅。 第二，铋阳离子具有大的玻恩有效电荷以提供高介电常数和带电缺陷的屏蔽。第三，无铅甲基碘化铋铵材料由于优先形成保护性氧化物层而在水蒸气存在下可以是相稳定的。 鉴于铅基有机金属卤化物钙钛矿材料的这些潜在优势，本研究的总体目标是通过理论和实验研究，对含铋化合物作为类钙钛矿太阳能光伏材料的光伏性能进行基本了解。 为此，研究有三个目标。 第一个目标是通过研究碱金属偏硫铋矿（少数几类不分层的Bi基材料之一）来研究对称性对良好输运性质的重要性。 第二个目标是开发模型，以确定复合过程和复合率的材料从时间分辨的光致发光测量。 第三个目标是发展策略，用于生长具有更高纯度的新Bi化合物，并将杂质含量与少数载流子寿命相关联。 密度泛函理论将用于确定电子结构、介电常数和电荷载流子有效质量。实验研究将建立有效吸收太阳能的材料设计标准，重点是确定颗粒内结构缺陷，分子阳离子和晶体对称性对传输扩散长度，光学特性和整体器件性能的作用。 薄膜的扩散长度将通过时间分辨的光致发光测量以及单光子和双光子光谱深度分辨的寿命测量，去耦的表面复合的影响。