Materials World Network: Nano-Structured InGaN Solar Cells Program

全世界都在努力通过太阳能电池增加发电量，以实现减少温室气体的目标。一个要求是高效多结太阳能电池（MJSC）从聚光太阳能发电（CSP）厂提取电力，这有望成为向国家和超级电网系统输送太阳能的核心。目前，这样的MJSC必须联合收割机结合不同的材料系统，并且通常受限于使各个电池晶格匹配以避免由于缺陷而导致的效率损失的要求。这项工作旨在通过研究基于InxGa 1-xN的太阳能电池来规避这些问题，InxGa 1-xN具有0.7-3.4 eV的直接带隙，跨越了大部分可见光谱，因此有希望从单一材料系统获得MJSC。为了避免晶格失配和材料质量的问题，这些问题将基于InxGa 1-xN外延层的原型太阳能电池限制在低x（x0.3），研究人员以纳米棒的形式生长InxGa 1-xN，使用已经开发的方法合并纳米棒以提供太阳能电池模板。这个团队集合了增长和设备制造方面的互补专业知识（美国）。诺丁汉）、结构表征（U.布里斯托）和纳米级光学和电学表征（亚利桑那州立大学）。和太阳能电池设计和表征（与NREL合作），旨在探索InxGa 1-xN单结电池在整个成分范围（0x 1）的特性，英国参与者获得英国工程和物理科学理事会的支持。该团队研究了InxGa 1-xN纳米棒的关键基本特性，使用透射和扫描电子显微镜来确定生长无缺陷InxGa 1-xN纳米棒阵列的材料要求，并克服晶格失配的问题。这项工作还研究了InxGa 1-xN纳米棒的电子特性，使用新的阴极发光和电子全息研究，以及时间分辨的光致发光。单结太阳能电池将被制造和表征为具有低和高In含量的InxGa 1-xN纳米棒，并且探索性工作将被进行到包括隧道结的新型双结纳米棒电池中，从而建立对InxGa 1-xN MJSC器件的未来发展的要求。这项工作的目的是建立InGaN作为基础（a）在整个可见光谱和（B）CSP工厂所需的高效率MJSC，通过使用一种新的纳米棒几何形状，以克服影响连续InGaN外延层的材料限制。该团队汇集了具有独特专业知识和技术组合的领导小组，旨在澄清关键材料问题，包括纳米棒和原型太阳能电池的基本特性。由于公众科学素养对制定健全的政策至关重要，项目教育/推广工作包括为亚利桑那州州立大学的“科学是有趣的”计划做出贡献，以开发适合4年级至12年级学生的45-60分钟课程。 其目的是（i）提高学生对科学和工程的兴趣，并鼓励在相关技术领域追求高等教育，以及（ii）阐明智力创新如何影响未来可再生能源的有效利用，并帮助亚利桑那州开发高科技产业的人力基础设施。 亚利桑那州立大学还开发了一门关于纳米结构光伏器件材料的新课程，将其纳入新设立的纳米科学硕士课程。

There is a worldwide effort to increase power generation through solar cells, to meet targets in reducing greenhouse gases. One requirement is for high efficiency multijunction solar cells (MJSCs) to extract power from concentrated solar power (CSP) plants, which are expected to become central to the delivery of solar power to national and super-grid systems. At present, such MJSCs must combine different materials systems and are usually limited by the requirement to lattice-match the individual cells to avoid efficiency losses due to defects. This effort aims to circumvent these problems by investigating solar cells based on InxGa1-xN, which has a direct band gap of 0.7-3.4 eV, spanning most of the visible spectrum, thus promising MJSCs from a single materials system. To avoid the problems of lattice mismatch and of material quality, which limit prototype solar cells based on InxGa1-xN epilayers to low x (x0.3), the investigators grow the InxGa1-xN in nanorod form, merging the nanorods using methods already developed to provide a solar cell template. The team assembled, which combines complementary expertise in growth and device fabrication (U. Nottingham), structural characterization (U. Bristol), and nanoscale optical and electrical characterization (Arizona State U.) and solar cell design and characterization (in collaboration with NREL), aims to explore the properties of InxGa1-xN single junction cells over the full composition range (0x1), with the UK participants receiving support from the Engineering and Physical Sciences Council of the UK. The team examines key fundamental properties of InxGa1-xN nanorods, using transmission and scanning electron microscopy to determine the materials requirements for growing defect-free InxGa1-xN nanorod arrays, and overcoming the problem of lattice mismatch. The work also examines the electronic properties of InxGa1-xN nanorods using novel cathodoluminescence and electron holography studies, and time-resolved photoluminescence. Single junction solar cells will be fabricated and characterized for InxGa1-xN nanorods with low and high In content, and exploratory work will be carried out into a novel two-junction nanorod cell including a tunnel junction, thus establishing the requirements for the future development of InxGa1-xN MJSC devices. The work aims to establish InGaN as a basis for (a) photovoltaics across the entire visible spectrum and (b) high efficiency MJSCs needed for CSP plants, by using a novel nanorod geometry to overcome the materials limitations that affect continuous InGaN epilayers. The team assembled brings together leading groups with a unique combination of expertise and techniques designed to clarify the key materials issues, including the fundamental properties of the nanorods and of prototype solar cells. As public science literacy is critical to the development of sound policy, project education/outreach efforts include contributions to the Arizona State University's "Science is Fun" program to develop a 45-60 minute lesson suitable for students in grades 4th through 12th. The objective is to (i) increase student interest in science and engineering and encourage the pursuit of advanced education in related technical fields, and (ii) elucidate how intellectual innovations can impact future efficient use of renewable energy, and help develop human infrastructure for the high-technology industry in Arizona. A new course on materials for nano-structured photovoltaic devices is also developed at Arizona State University to be included in the curriculum of the newly established Science Master's in Nanoscience program.