UNS: Defect Engineering in Zinc-Blende-Type Absorbers

太阳代表着地球上最丰富的潜在可持续能源。用于发电的太阳能电池需要吸收太阳能量并将其光子转化为电子的材料，这一过程被称为光伏发电。虽然由晶体硅制成的太阳能电池目前占全球太阳能光伏市场的90%左右，但由地壳中丰富的非常薄的非硅材料层制成的替代太阳能电池具有许多优点。这包括大幅降低材料消耗和低成本制造，以及灵活或可折叠、重量超轻、能够轻松集成到建筑结构中的新形状因素。不幸的是，基于地壳中丰富元素的新材料无法与刚性晶体硅基材料的太阳能到电力的转换效率相匹配，因此目前没有竞争力。该项目旨在从根本上了解一种基于锌混合物的有前途的薄膜光伏材料的能量转换性能，这种材料是由地壳中丰富的无毒元素的混合物制成的，而且相对便宜。这项研究将集中于控制这些材料中的原子水平紊乱，最终为低成本、可扩展、高性能的太阳能光伏发电提供一条可行的途径。这项研究还将在可持续能源材料发展的重要领域吸引和培养新一代的本科生、研究生和博士后科学家。研究结果也将被纳入杜克大学本科和研究生水平的材料科学课程。目前商业用途的薄膜太阳能光伏材料，包括CIGS和Cd-Te基材料，含有在地壳中昂贵或稀有的元素（如铟、碲）或存在毒性问题（如镉）。这些可持续性问题可能会限制未来的成本降低和市场份额。最近，由（Cu）2-ZnSn-(S,Se)4-(CZTSSe)制成的kesteri基薄膜太阳能电池，其中CIGS-Se材料中的铟/镓被更容易获得且成本更低的元素锌/锡取代，其转换效率高达12.6%。然而，这种效率仍然只有最好的晶体硅或薄膜商业太阳能光伏材料的一半左右。本研究假设当前锌-闪锌矿材料基体（如Cu on Zn， Zn on Cu）的反位结构紊乱导致电势能波动和带尾，有效地限制了开路电压。本研究的总体目标是了解硫族铜基锌-闪锌矿太阳能光伏材料的反位无序性质，并通过合理的计算和实验材料设计方法相结合，设计出可以控制和降低反位无序水平的新型闪锌矿材料。研究计划有三个目标。第一个目标是计算评估PV吸收器的潜在锌掺杂相关材料，重点是确定导致更良性的基于重组的缺陷和晶界的材料特征。第二个目标是设计和合成稳定的CZTSSe类似物，具有较低的反位点紊乱和带尾倾向。最后，第三个目标是研究不同数量的反位无序对材料及其器件性能的影响。项目目标的实现将为理解复杂能量收集材料的缺陷控制提供一个框架，并为新型可扩展和高效的太阳能光伏设备提供一条途径。

PI: David MitziProposal Number: 1511737The 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. While solar cells made from crystalline silicon currently have about 90 percent of the worldwide solar photovoltaics (PV) market, alternative solar cells made from very thin layers of non-silicon materials abundant in the earth's crust offer a number of advantages. These include dramatically reduced materials consumption and low-cost fabrication, as well as new form factors that are flexible or foldable, ultralight in weight, and enable facile integration into building structures. Unfortunately, new materials based on elements abundant in the earth's crust cannot match the sunlight-to-electric power conversion efficiency of rigid crystalline silicon-based materials, and so are presently not competitive. This project seeks to gain fundamental understanding of the power conversion performance one promising class of thin-film photovoltaic materials based on zinc blends, which are made from a mixture of nontoxic elements abundant in the earth's crust and are relatively inexpensive. The research will focus on controlling the atomic level disorder within these materials to ultimately provide a viable pathway to low-cost, scalable, high-performance solar photovoltaics. The research will also engage and train a new generation of undergraduate, graduate and postdoctoral scientists in the important area of sustainable energy materials development. Results from the research will also be incorporated into undergraduate and graduate level materials science courses at Duke University. Current thin film solar photovoltaic materials in commercial use, including CIGS and Cd-Te based materials, contain elements that are either costly or rare in the earth's crust (e.g., indium, tellurium) or present toxicity issues (e.g., cadmium). These sustainability issues potentially impose limits on future cost reduction and market share. Recently, kesterite-based thin-film solar cells made of (Cu)2-ZnSn-(S,Se)4-(CZTSSe), in which indium/gallium in CIGS-Se materials are replaced by more readily available and lower-cost elements zinc/tin, have achieved conversion efficiencies of up to 12.6%. However, this efficiency is still only about one-half that of the best crystalline silicon or thin-film commercial solar PV materials. The proposed research is based on the hypothesis that anti-site structural disorder in current zinc-blende material matrices (e.g., Cu on Zn, Zn on Cu) lead to electrical potential energy fluctuations and band tailing that effectively limits the open-circuit voltage. The overall goals of this research are to understand the nature of anti-site disorder in copper chalcogenide based zinc-blende materials for solar PV, and to design new blende materials in which the level of anti-site disorder can be controlled and reduced through a combination of rational computational and experimental materials design approaches. The research plan has three objectives. The first objective is to computationally evaluate prospective zinc-blende-related materials for PV absorbers, focusing on identifying the materials features that lead to more benign recombination-based defects and grain boundaries. The second objective is to design and synthesize stable CZTSSe analogs that have a lower propensity towards anti-site disorder and band tailing. Finally, the third objective is to study the impact of varying amounts of anti-site disorder on materials and their device properties. Achievement of the project goals will provide a framework for understanding defect control in complex energy harvesting materials and offer one pathway to new scalable and high-efficiency solar PV devices.