Understanding Excitons for Lead-Free Perovskite Photovoltaics

太阳代表着地球上最丰富的潜在的无污染能源。用于发电的太阳能电池需要吸收太阳的材料。并将其光子转化为电子，这一过程被称为光伏发电。寻找最好的光伏材料是太阳能电池研究的一个活跃领域。最近，一种令人兴奋的新型光伏材料——有机金属钙钛矿出现了。这些材料具有生产成本低、使用地球上丰富的元素和材料等优点。目前拥有超过15%的太阳能转换效率。需要进一步的研究来调整这些材料的光学特性，以提高光吸收，将效率提高到20%以上，与硅太阳能电池竞争，并从材料基体中去除有毒的铅。该项目的目标是获得对有机金属钙钛矿有益的电子和光学性质的基本理解，以解决这两个问题。先进的计算方法将用于在原子水平上预测有机金属钙钛矿的电子和光学性质，以研究量子力学如何在太阳能光伏应用中这些材料的性能中发挥作用。将进行模型模拟，以确定铅的替代品，保持理想的太阳能吸收特性。科学成果将以博客形式更新向公众提供，并将向科学界提供一个数据库，以确认这些发现并利用这些信息。此外，该项目将为材料科学研究生和本科生提供先进超级计算机技术方面的培训，为这一国家劳动力需求的关键领域提供训练有素的科学家。最近，有机金属钙钛矿，特别是那些基于铅的，已经成为一种令人兴奋的新型地球丰富的光伏材料，太阳能转换效率超过15%，并且具有低制造成本的潜力。该项目的目标是通过先进的计算模型获得对有机金属钙钛矿的激子和光学性质的基本理解，然后使用这种方法确定材料基质中铅的替代品。钙钛矿材料体系通过替换不同的组成原子，为改进提供了较大的相空间。然而，为了有针对性的发展，需要对电子相关性，特别是控制激子和电荷输运性质的物理学有一个基本的了解。在这方面，在具有光学和激子性质的钙钛矿晶体结构体系中，自由载流子之间的相互作用是未知的。基于多体摄动理论的理论光谱学技术将被用于对具有不同成分离子的钙钛矿卤化物材料中的光物质相互作用的基本理解。基于赫丁的第一性原理技术？s近似值和精确计算量子力学、电子-电子和电子-空穴相互作用的Bethe-Salpeter方程将用于预测带隙、有效载流子质量和光学吸收光谱。通过考虑准粒子能量、激子效应以及与自由载流子的相互作用，该方法将为钙钛矿的光学吸收过程提供机理见解。该项目还将研究不同成分，特别是含和不含铅离子的系统对这些光学吸收过程的影响。研究成果将以博客形式向公众发布，计算结果将提供给科学界继续验证。此外，本项目将为材料科学研究生和本科生提供超级计算平台上先进原子建模技术的培训。

Principal Investigator: André SchleifeNumber: 1437230Nontechnical DescriptionThe sun represents the most abundant potential source of pollution-free 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. The search for the best photovoltaic material is an active area of solar cell research. Recently, an exciting new class of photovoltaic materials called organo-metal perovskites has emerged. These materials are promising because they have low production cost, use elements and materials abundant in the earth?s crust, and currently possess solar energy conversion efficiencies of over 15%. Further research is needed to tune the optical properties of these materials to improve light absorption needed to push the efficiencies over 20% to be competitive with silicon solar cells, and to remove lead, which is toxic, from the material matrix. The goal of this project is to gain a fundamental understanding of the beneficial electronic and optical properties of organo-metal perovskites to address these two issues. Advanced computational approaches will be used to predict electronic and optical properties of organo-metal perovskites at the atomic level to study how quantum mechanics plays a role in the performance of these materials for solar photovoltaic applications. Model simulations will be performed to identify replacements for lead that maintain desirable solar energy absorption characteristics. Scientific results will be made available to the public in blog-style updates, and a database will be provided to the scientific community to confirm the findings and make use of this information. In addition, in this project will provide training of material science graduate and undergraduate students in advanced supercomputer techniques needed to provide a pipeline of trained scientists in this critical area of national workforce need. Technical DescriptionRecently, organo-metal perovskites, especially those based on lead, have emerged as an exciting new class of earth-abundant photovoltaic materials with solar energy conversion efficiencies exceeding 15% and potential for low manufacturing cost. The goal of this project is to gain a fundamental understanding of the excitonic and optical properties of organo-metal perovskites through advanced computational models, and then use this approach to identify replacements for lead in the material matrix. The perovskite material system offers a large phase space for improvement by replacing different constituent atoms. However, for targeted development, a fundamental understanding of electronic correlations, particularly the physics that governs the excitonic and charge-transport properties, is needed. In this regard, the interplay between free carriers in systems with perovskite crystal structures that possess optical and excitonic properties is unknown. Theoretical spectroscopy techniques based on many-body perturbation theory will be used to achieve a fundamental understanding of light-matter interaction in perovskite-halide materials with different constituent ions. First-principles techniques based on Hedin?s approximation and the Bethe-Salpeter equation, which accurately computes quantum-mechanical, electron-electron, and electron-hole interactions, will be used to predict band gaps, effective carrier masses, and optical absorption spectra. By taking into account quasi-particle energies, excitonic effects, and the interplay with free carriers, this approach will provide mechanistic insights into the optical absorption process in perovskites. This project will also investigate the influence of different constituents, particularly systems with and without lead ions, on these optical absorption processes. The research outcomes will be made available to the public in blog-style updates, and the computational results will be provided to the scientific community for continued validation. In addition, in this project will provide training of material science graduate and undergraduate students in advanced atomistic modeling techniques on supercomputing platforms.