Collaborative Research: High Efficiency Tandem Perovskite-Copper Indium Selenide Solar Cell

摘要：非技术：太阳能光伏（PV）能源转换是低成本发电替代煤电的重要技术。这对于为世界上目前缺乏电网的一半人口提供电力也非常重要。为了经济地生产光伏发电，太阳能电池的效率是一个非常重要的考虑因素，因为与面积相关的成本，如封装、布线和结构，随着电池效率的提高而成比例地降低。该领域最近的一个发展是发现了一种新的薄膜材料，即有机-无机金属卤化物基钙钛矿的杂化，可用于产生光伏发电，转换效率约为20%。这种新材料比常用的薄膜材料（如铜铟镓硒化物（CIGS））具有更大的带隙，因此可以用作具有CIGS的单片串联太阳能电池排列中的高带隙第一电池。计算预测，这种串联串联电池结构可以将薄膜CIGS太阳能电池的效率从目前的20%提高到30%，提高了50%。本课题旨在进行基础材料和器件的研究，以实现这种高效率的串联电池结构。人们希望这种结构将导致进一步的发展，从而显著降低太阳能发电的成本。本项目将有一名研究生参与，新教材将被纳入太阳能转换课程。技术：该方案的重点是设计和制造一种单片串联电池结构，将高间隙钙钛矿电池沉积在高效CIGS电池的顶部。这两个细胞通过新型隧道连接在一起。为了实现这一概念，需要开发一些新的材料、工艺和设备结构。其中包括：一种钙钛矿材料，其带隙在1.7-1.8 eV范围内，而不是目前的1.57 eV材料。为了使CIGS底电池高效串联电池，需要更高的带隙。我们将开发高效的Pb（I-Br）钙钛矿来增加带隙。-钙钛矿材料，在较高温度下物理稳定，因此可以在设备上沉积透明触点，使光线从电池顶部入射。我们将使用新的有机前体，如碘化甲脒和氢碘化尿素来获得热稳定的钙钛矿。-在更高温度下沉积钙钛矿的新真空工艺，避免了溶液生长过程的不稳定性。-利用无机异质结层进行电子和空穴提取，从而避免了不稳定的有机异质结层。-ITO/ZnO隧道结连接两个电池。-通过采用带隙分级策略以及更大的晶粒生长和故意掺杂Na或K，实现了1.1至1.15 eV范围内的高效CIGS电池。该项目包括全面的材料和器件分析任务，以了解器件的物理特性。

Abstract:Non-technical:Solar photovoltaic (PV) energy conversion is an important technology for generating low-cost electricity to replace coal-generated power. It is also very important for providing electricity to half of the people in the world who currently lack grid-connected power. For economical generation of PV power, efficiency of solar cells is a very important consideration, since area-related costs such as encapsulation, wiring and structure decrease proportionately as the efficiency of the cell increases. A very recent development in this field has been the discovery that a new thin film material, hybrid organic-inorganic metal halide based perovskites, can be used to generate PV power with a conversion efficiency of ~20%. This new material has a larger bandgap than commonly used thin film materials such as copper-indium-gallium selenide (CIGS), and therefore, can be used as a higher bandgap first cell in a monolithic tandem solar cell arrangement with CIGS. Calculations predict that such a series-connected tandem cell structures can increase the efficiency of thin film CIGS solar cells to 30% from the current value of 20%, a 50% increase. This proposal is aimed towards fundamental material and device research to achieve such high efficiency tandem cell structures. It is hoped that such a structure will lead to further developments which result in a significant decrease in the cost of solar-electric power. A graduate student will participate in this project and new teaching materials will be incorporated into courses dealing with solar energy conversion.Technical:The proposal is focused on designing and fabricating a monolithic tandem cell structure with a high gap perovskite cell deposited on top of a high efficiency CIGS cell. The two cells are connected using novel tunnel junctions. Several new materials, processes and device structures need to be developed for the concept to work. Among these are:-A perovskite material with a bandgap in the 1.7-1.8 eV range as opposed to the current 1.57 eV material. The higher bandgap is needed to make efficient tandem cells with a CIGS bottom cell. We will develop efficient Pb(I-Br) perovskites to increase the bandgap.-A perovskite material which is physically stable at higher temperatures so that transparent contacts can be deposited on the device to allow light to be incident form the top of the cell. We will use novel organic precursors such as formamidinium iodide and urea hydroiodide to achieve thermally stable perovskites.-A new vacuum process for depositing perovskites at higher temperatures which avoids the instability of the solution growth process.-The use of inorganic heterojunction layers for electron and hole extraction , thus avoiding unstable organic heterojunction layers.-ITO/ZnO tunnel junctions to connect the two cells.-Innovative CIGS cells in1.1 to1.15 eV range with high efficiency achieved by using bandgap grading strategies along with larger grain growth and deliberate Na or K doping.The project includes comprehensive material and device analysis tasks so as to understand the physics of the device.