Instilling Defect-Tolerance in ABZ2 Photovoltaic Materials

该项目旨在开发一种新型的用于光伏(PV)的半导体，这种半导体可以容忍缺陷，从而在以低资本密集型和可扩展的方法制造时实现高效率。PVS利用阳光产生清洁电力，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年实现立法规定的二氧化碳净零排放目标。迫切需要新的薄膜光伏材料。薄膜PV可用于串联器件结构，在这种结构中，它们被沉积在主导市场的硅PV或较小带隙的薄膜PV的顶部。这些串联设备将更大比例的太阳能光谱转换为电能，可以实现超过最好的单结设备的效率，这对于加快公用事业规模的光伏部署至关重要。薄膜PVs还可以用作收集能量的屋顶瓦片、窗户或覆层，以实现可持续的碳中性建筑。但在所有应用中，使用低成本制造方法制造材料时，高效是至关重要的。限制因素是点缺陷的有害作用，如空位。在传统半导体中，这些点缺陷在带隙深处引入能级，造成不可逆转的能量损失。要将这些缺陷的密度降至最低，通常需要昂贵的制造工艺。缺陷容限半导体通过在接近带边(即，浅)的地方形成缺陷能级，从而绕过这些限制，在那里它们的危害性较小。在最近偶然发现卤化铅钙钛矿之前，这种材料一直很少见。这些多晶材料通过溶液处理以低成本生长，其缺陷比硅多100万倍，但在PV中已经比多晶硅更有效。一个关键的问题是，是否可以在其他类别的材料中找到缺陷容忍度，这些材料没有卤化物钙钛矿的毒性负担。这项工作旨在开发一套精确定位无铅耐缺陷半导体的设计规则，并系统地将这些材料开发成可部署在太瓦级的高效、稳定的PV。所研究的材料为ABZ2化合物，其中A为一价阳离子，B为二价阳离子，Z为二价阴离子。这些材料已经显示出有希望的迹象，暗示了缺陷容忍度。我的方法利用了我在控制复杂薄膜方面的实验优势。我假设，形成浅陷阱的物质可以通过它们的晶体结构、带边轨道组成和阳离子-阴离子轨道重叠程度来识别。我将通过调整一小组ABZ2材料的组成来实验地阐明每种属性的作用，以一次改变一种属性。缺陷容忍度将通过故意诱导空位并测量它们对电荷载流子寿命和电子结构的影响来衡量。这些设计规则将被应用于确定最有希望的ABZ2材料，这些材料将通过可扩展的溶液和蒸气方法生长。我将使用快速的实验反馈循环来优化它们的生长，以获得具有良好的太阳能吸收器整体性能的材料。这种材料将被开发成PV，吸取我在设备工程方面的技能和经验。这项工作非常及时，将使容错半导体这一新兴领域远离有毒的钙钛矿。这些新材料最终可能成为串联式或建筑集成式PV的商业竞争者，从而对GB 120B光伏行业产生影响。这些新材料还可以产生更广泛的影响，并被用作廉价但高效的材料，用于清洁太阳能燃料生产或生物传感器。这个项目为实现这些令人兴奋的可能性奠定了关键基础，并将使我能够用一个尖端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.