Plugging the 1 eV band gap gap: GaAsBiN as a highly mismatched alloy for multi-junction photovoltaics.

在这个项目中，将对GaAsBiN的生长物理进行研究，最终展示这种材料在高效光伏领域的潜力。研究人员正在努力实现太阳能电池效率超过50%，并提出了更多深奥的器件设计来推动效率极限。成熟的多结器件设计(在不同的子电池中获取不同区域的太阳光谱)理论上的效率极限远远超过50%。然而，目前的世界纪录效率只有46%。缺乏高质量的亚电池材料阻碍了这些器件的发展。一个好的候选材料将吸收太阳光谱的适当区域，并结合到现有的多结设计中，而不会在结构中造成应变，从而降低太阳能电池的性能。本研究中提出的合金--砷化镓双胺氮化物(GaAsBiN)是一种理想的候选材料。铋和氮对砷化镓电子结构的巨大影响使得合金的光学吸收轮廓可以很容易地定制；铋原子的大尺寸平衡了氮原子的小尺寸，也使得合金可以无应变地融入现有的器件设计中。然而，合成GaAsBiN的技术挑战限制了其发展。As、Bi和N之间的尺寸差异使GaAsBiN晶体生长成为问题，需要非标准的生长条件和技术。世界上很少有实验室报道GaAsBiN的生长，只有一个实验室展示了包含这种材料的器件。该项目将分三个工作包完成：该项目的第一个工作包将包括初步生长研究，旨在生产简单的GaAsN、GaAsBiN和GaAsBiN测试样品。从之前公布的生长参数开始，材料质量将通过生长条件调查进行优化。在第二个工作包中，从工作包一中获得的生长参数将用于生产几个GaAsBiN器件，这些器件将使用标准电子技术进行表征。同时，选定的生长参数将用于生长GaAsBiN薄层，这将在谢菲尔德大学以原子分辨率成像，并将在哈德斯菲尔德大学以原子层分辨率测量其铋分布。通过仔细分析表面图像和铋分布，并将这些结果与相应的电子器件性能进行比较，将确定生长条件对材料成分和质量的影响。工作封装三将利用WP2中开发的生长条件了解来生产一系列GaAsBiN器件，并对其进行表征，以确定其光电性能和对多结太阳能电池的适用性。

In this project, the growth physics of GaAsBiN will be investigated, culminating in a demonstration of the potential of this material for high efficiency photovoltaics.Researchers are striving to achieve solar cell efficiencies over 50 %, with ever more esoteric device designs being proposed to push efficiency limits. The well-established multi-junction device design (which harvests different regions of the solar spectrum in different sub-cells) has a theoretical efficiency limit well in excess of 50 %. However, the current world record efficiency is only 46 %. A lack of high quality sub-cell materials is hindering the development of these devices. A good candidate material will absorb an appropriate region of the solar spectrum and incorporate into existing multi-junction designs without causing strain in the structure, which degrades solar cell performance.The alloy proposed in this research, gallium arsenide bismide nitride (GaAsBiN), is an ideal candidate material. The dramatic impacts of Bi and N on the GaAs electronic structure allow the optical absorption profile of the alloy to be easily tailored; the large size of the Bi atom balancing the small size of the N atom also allows the alloy to be incorporated into existing device designs strain-free. However, the technical challenge of synthesising GaAsBiN has limited its development to date. The size differences between As, Bi and N make GaAsBiN crystal growth problematic, necessitating non-standard growth conditions and techniques. Very few laboratories around the world have reported GaAsBiN growth and only one has demonstrated a device comprising this material.The project will be completed in three work packages:The first work package of this project will involve preliminary growth studies aimed at producing simple GaAsN, GaAsBi, and GaAsBiN test samples. Starting with previously published growth parameters, the material quality will be optimised through a growth condition investigation.In the second work package, the growth parameters derived in work package one will be used to produce several GaAsBiN devices, which will be characterised using standard electronic techniques. In parallel, selected growth parameters will be used to grow thin GaAsBiN layers, which will be imaged with atomic resolution at the University of Sheffield and will have their Bi profiles measured with atomic layer resolution at the University of Huddersfield. Through careful analysis of the surface images and Bi profiles, and comparison of these results with the corresponding electronic device performances, the impact of growth conditions on material composition and quality will be determined.Work package three will use the growth condition understanding developed in WP2 to produce a series of GaAsBiN devices, which will be characterised to determine their opto-electronic performance and applicability for multi-junction solar cells.