Improving the Understanding of CZTS-Se as a Solar Absorber Material through Single Crystals Formed Using Phase Diagram Analysis

通过相图分析形成的单晶提高对 CZTS-Se 作为太阳能吸收材料的理解

• 批准号: 1796442
• 金额: --
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1796442
• 关键词: Improving; Understanding; CZTS; Se; Solar

The aim of this project is examine the electronic and structural characteristics of the low-cost quaternary semiconductor CZTS-Se (chemical formula Cu2ZnSn(S,Se)4). This is intended to inform the use of CZTS-Se for thin-film solar photovoltaic applications. The project aims to gain a deeper understanding of the phase diagram structure and crystallisation processes of CZTS-Se in different solvents, along with the resultant effect on electronic properties. Central to this analysis is the fabrication of large, single crystals of CZTS-Se which would allow characterisation of the material's bulk properties in the absence of surface effects. This is in order to inform solution processing methods of CZTS-Se solar cell fabrication to reach higher efficiencies than the current record.The motivation for this study is the fact that CZTS-Se devices can be fabricated from cheap, abundant and non-toxic elements. The low price of raw materials coupled with a low disposal cost due to non-toxicity means CZTS-Se devices have the potential to form very cheap solar-power modules. Another advantage to these devices is that as a solid, polycrystalline semiconductor, CZTS-Se does not suffer from the instability issues that limit the viability of organic and perovskite devices at present. This makes it more feasible to create modules that last long enough to provide the necessary returns. Due to these desirable features, if CZTS-Se modules were able to enter the energy market they could significantly reduce the price of solar power around the world. However, despite being a direct-gap semiconductor with a band-gap that is close to optimal, the current record of efficiency for a CZTS-Se solar device is only 12.6%, compared to just over 25% for the champion silicon modules. This low efficiency means that the rate-of-return for CZTS-Se devices is currently too low for them to be economical.Device efficiency in photovoltaic devices can be understood as a dependence upon 3 parameters: the short circuit current, JSC; the open-circuit voltage, VOC; and the fill factor, FF. CZTS-Se devices have already been able to demonstrate similar values of JSC to devices made of CIGS, an already-established quaternary semiconductor, but the VOC for CZTS-Se is significantly below the equivalent level for CIGS. Addressing the 'VOC- deficit' in CZTS-Se is therefore a major aim of this project. The presence of charge-carrier recombination centres is thought to contribute to the VOC- deficit, where potential sites for recombination include crystal grain boundaries and/or defects in the bulk material. Another factor found to contribute to poor device performance is the formation of secondary compositional and/or structural phases.As a result, this project is focussed upon removing grain-boundaries altogether by forming a large, single crystal of CZTS-Se. Single crystal growth for CZTS has been successfully demonstrated in the past. Therefore our aim is to develop a process to grow single crystals and measure their photovoltaic properties. These properties can then be compared with polycrystalline CZTS-Se to assess the effect of grain boundaries. A single crystal of CZTS-Se will also allow the effects of bulk defects and secondary phases to be investigated, separate from surface effects. Variations in the elemental composition and fabrication conditions to reduce detrimental bulk defects and secondary phases can then be explored.Production and characterisation of single crystals requires a deep understanding of the solutions formed from CZTS-Se with a range of solvents. Therefore much of the work of this project will be to characterise phase diagrams of CZTS-Se/solvent systems across a range of temperatures and compositional ratios.The primary concern of this project is the fundamental analysis of CZTS-Se as a material. However we intend that the insights from this project will be applied to the production of high-quality CZTS-Se absorber layers.

本项目的目的是研究低成本的四元半导体CZTS-Se(化学式为Cu2ZnSnO(S，Se)4)的电子和结构特性。这旨在告知CZTS-Se在薄膜太阳能光伏应用中的使用情况。该项目旨在更深入地了解CZTS-Se在不同溶剂中的相图结构和结晶过程，以及由此产生的对电子性质的影响。这种分析的核心是CZTS-Se大单晶的制造，这将允许在没有表面效应的情况下表征材料的整体性质。这是为了给CZTS-Se太阳能电池制造的溶液处理方法提供参考，以达到比当前记录更高的效率。这项研究的动机是这样一个事实，即CZTS-Se器件可以由廉价、丰富和无毒的元素制造而成。原材料的低价格加上无毒的低处理成本意味着CZTS-Se器件有可能形成非常便宜的太阳能组件。这些器件的另一个优点是，作为一种固体多晶半导体，CZTS-Se目前不存在限制有机和钙钛矿型器件生存能力的不稳定性问题。这使得创建持续足够长的模块来提供必要的回报变得更加可行。由于这些令人向往的功能，如果CZTS-Se组件能够进入能源市场，它们可以显著降低世界各地的太阳能电价。然而，尽管CZTS-Se是一种直接带隙半导体，其带隙接近最佳，但目前CZTS-Se太阳能器件的效率纪录仅为12.6%，而冠军硅模块的效率仅略高于25%。这种低效率意味着CZTS-Se器件目前的回报率太低而不经济。光伏器件中的器件效率可以理解为依赖于三个参数：短路电流JSC、开路电压VOC和填充系数Ff。CZTS-Se器件已经能够展示出与由CIGS制成的器件相似的JSC值，但CZTS-Se的VOC明显低于CIGS的同等水平。因此，解决CZTS-Se的VOC赤字问题是本项目的一个主要目标。电荷-载流子复合中心的存在被认为是造成VOC亏损的原因，其中潜在的复合位置包括晶体晶界和/或块体材料中的缺陷。另一个导致器件性能不佳的因素是二次成分和/或结构相的形成。因此，这个项目的重点是通过形成大的CZTS-Se单晶来完全消除晶界。CZTS单晶生长已经在过去得到了成功的证明。因此，我们的目标是开发一种生长单晶并测量其光伏性能的工艺。然后可以将这些特性与多晶CZTS-Se进行比较，以评估晶界的影响。CZTS-Se的单晶也将允许研究体缺陷和第二相的影响，而不是表面效应。然后，可以探索元素组成和制备条件的变化，以减少有害的体缺陷和第二相。单晶的生产和表征需要对CZTS-Se与一系列溶剂形成的溶液有深入的了解。因此，本项目的大部分工作将是在一定的温度和组成比范围内表征CZTS-Se/溶剂体系的相图。本项目主要关注的是CZTS-Se作为材料的基本分析。然而，我们打算将该项目的见解应用于高质量CZTS-Se吸收器层的生产。