Instilling Defect-Tolerance in ABZ2 Photovoltaic Materials

该项目旨在为光伏（pv）开发一种新型半导体，这种半导体可以容忍缺陷，从而在低资本强度和可扩展的方法下实现高效率。光伏发电从阳光中产生清洁电力，它们在英国的部署需要加快一个数量级以上，这样我们才能在2050年实现二氧化碳净零排放的立法目标。迫切需要新型薄膜光伏材料。薄膜pv可用于串联器件结构，其中它们沉积在硅pv（主导市场）或更小带隙薄膜pv的顶部。这些串联装置将太阳光谱的更大一部分转换为电能，并且可以实现超过最佳单结装置的效率，这对于加速公用事业规模的光伏部署至关重要。薄膜光伏也可以用作能量收集的屋顶瓦片、窗户或包层，以实现可持续的碳中和建筑。但在所有的应用中，重要的是，当用低成本的制造方法制造时，材料是高效的。限制因素是点缺陷的有害作用，如空位。在传统的半导体中，这些点缺陷在带隙深处引入能级，并造成不可逆转的能量损失。最小化这些缺陷的密度通常需要昂贵的制造路线。耐缺陷半导体通过形成靠近带边缘的缺陷水平（即，浅）来规避这些限制，在那里它们的危害较小。在最近偶然发现卤化铅钙钛矿之前，这种材料一直很罕见。这些多晶硅材料通过溶液法廉价生长，其缺陷是硅的100多万倍，但在pv中已经比多晶硅效率更高。一个关键的问题是，是否可以在没有卤化物钙钛矿的毒性负担的其他类别的材料中发现缺陷耐受性。这项工作旨在制定一套设计规则，以确定无铅耐缺陷半导体，并系统地将这些材料开发成可在太瓦规模上部署的高效、稳定的pv。重点研究的材料是ABZ2化合物，其中A是一价阳离子，B是二价阳离子，Z是二价阴离子。这些材料已经显示出良好的耐缺陷迹象。我的方法借鉴了我在复杂薄膜控制方面的实验优势。我假设形成浅阱的材料可以通过它们的晶体结构、带边轨道组成和正负离子轨道重叠程度来识别。我将通过实验来阐明每个属性的作用，通过调整一小组ABZ2材料的组成来每次改变一个属性。缺陷容限将通过有意诱导空位和测量其对载流子寿命和电子结构的影响来测量。这些设计规则将应用于确定最有前途的ABZ2材料，这些材料将通过可扩展的溶液和基于蒸汽的方法生长。我将使用快速实验反馈回路优化它们的生长，以获得具有前景的太阳能吸收体体积特性的材料。这些材料将被开发成pv，利用我在设备工程方面的技能和经验。这项工作非常及时，将使耐缺陷半导体的新兴领域远离有毒的钙钛矿。这种新材料最终可以成为串联或建筑集成光伏的商业竞争者，从而影响1200亿英镑的光伏产业。这些新材料还可以产生更广泛的影响，例如，作为清洁太阳能燃料生产或生物传感器的廉价但高效的材料。这个项目为实现这些令人兴奋的可能性奠定了关键的基础，并使我能够用一个前沿的项目来建立我的团队。

This project aims to develop a new class of semiconductors for photovoltaics (PVs) that can tolerate defects to achieve high efficiencies when manufactured by low capital-intensity and scalable methods. PVs produce clean electricity from sunlight, and their deployment in the UK needs to accelerated by over an order of magnitude so that we can meet our legislated net-zero CO2 emissions target by 2050. New thin film PV materials are urgently needed. Thin film PVs can be used in tandem device structures, in which they are deposited on top of silicon PVs (which dominate the market) or smaller-bandgap thin film PVs. These tandem devices convert a larger fraction of the solar spectrum into electrical energy and can achieve efficiencies surpassing the best single-junction devices, which will be vital for accelerating utility-scale PV deployment. Thin film PVs can also be used as energy-harvesting roof-tiles, windows or cladding to enable sustainable carbon-neutral buildings. But across all applications, it is essential that the materials are efficient when made with by low cost manufacturing methods. The limiting factor is the deleterious role of point defects, such as vacancies. In traditional semiconductors, these point defects introduce energy levels deep within the bandgap and cause irreversible losses in energy. Minimising the density of these defects often requires expensive manufacturing routes. Defect-tolerant semiconductors circumvent these limitations by forming defect levels close to the band-edges (i.e., shallow), where they are less harmful. Such materials were rare until the recent serendipitous discovery of the lead-halide perovskites. Grown cheaply by solution-processing, these polycrystalline materials have over a million times more defects than silicon but are already more efficient in PVs than multi-crystalline silicon. A critical question is whether defect-tolerance can be found in other classes of materials that are free from the toxicity burden of the halide perovskites. This work aims to develop a set of design rules to pinpoint lead-free defect-tolerant semiconductors, and systematically develop these materials into efficient, stable PVs that can be deployed on the terawatt scale. The materials focussed on are ABZ2 compounds, where A is a monovalent cation, B a divalent cation and Z a divalent anion. These materials already show promising signs hinting at defect-tolerance. My approach draws off my experimental strengths in the control of complex thin films. I hypothesise that materials forming shallow traps can be identified through their crystal structure, band-edge orbital composition and degree of cation-anion orbital overlap. I will experimentally elucidate the role of each property by tuning the composition of a small set of ABZ2 materials to vary one property at a time. Defect tolerance will be measured by intentionally inducing vacancies and measuring their effect on charge-carrier lifetime and electronic structure. These design rules will be applied to identify the most promising ABZ2 materials, which will be grown by scalable solution- and vapour-based methods. I will optimise their growth using a fast experimental feedback loop to achieve materials with promising bulk properties for solar absorbers. Such materials will be developed into PVs, drawing off my skills and experience in device engineering. This work is extremely timely and will lead the emerging area of defect-tolerant semiconductors away from toxic perovskites. The new materials can ultimately become commercial contenders for tandem or building-integrated PVs, and therefore impact on the £120B PV industry. These new materials can also have much broader impact and be used, for example, as cheap but efficient materials for clean solar fuel production or biosensors. This project sets the key foundations for achieving these exciting possibilities and will enable me to set-up my group with a cutting-edge programme.