Interfacial Engineering of Solution-Processed Thin-Film Photovoltaic Devices

英国已经设定了一个具有法律约束力的目标，即到2050年在经济的各个方面实现净零碳排放，而提供可持续和绿色的太阳能发电将是这一转型的关键。晶体硅目前主导着太阳能产业，约占目前销售的太阳能组件的95%。然而，由于其低光子吸收系数和间接带隙，需要高达350 m的厚度，这使得晶体Si不适合薄膜应用。柔性基板上的薄膜光伏（PV）材料将允许将太阳能转换集成到城市环境中的建筑物和基础设施中，这是扩大太阳能以满足所需环境目标的关键领域。Cu2ZnSn(S,Se)4 （CZTSSe）是一种无毒的无机薄膜材料，在AM1.5G照明下，其直接带隙可调谐在1.0 - 1.5 eV之间，理论功率转换效率（PCE）为20%，具有理想的光伏性能。然而，CZTSSe目前受到严重电压损失的限制，这与结构紊乱有关，包括反位缺陷、二次相和点缺陷簇，阻碍了PCE。该博士学位是英国布里斯托尔大学、诺森比亚大学和拉夫堡大学在SolPV项目上的合作的一部分，该项目由EPSRC与过程创新中心、庄信万、BAE系统和M-Solv的工业合作伙伴共同资助。本博士的主要目的是在CZTSSe吸收层和缓冲层之间进行p-n结的界面工程，使用原子层沉积，以实现大于15%的破纪录效率。作为最先进的CuInxGa1-x(S,Se)2 （CIGS）技术的缓冲材料，CdS已被广泛用作CZTSSe太阳能器件的缓冲层。虽然Cd在CZTSSe和CIGS中都是有效的缓冲层，但Cd是有毒的，不能释放到环境中，因此需要合适的替代品。铟基和锌基硫化氧替代品将作为可能的替代品进行研究。该项目的另一个目标是通过优化制造方法来控制吸收材料的结晶和组成，减少有害缺陷、深锡阱状态和碳杂质的形成。薄膜的体积和表面组成和结构将通过电子显微镜技术，拉曼显微镜和能量过滤光发射电子显微镜（EF-PEEM）进行检查。EF-PEEM可以在吸收-缓冲连接处提供局部有效功函数的表面电子映射，允许独特和重要的电子信息。这项研究的重点将是确认CZTSSe太阳能电池的PCE将超过15%，同时也使用可扩展的制造路线，以确保顺利过渡到工业应用。该项目属于EPSRC的“太阳能技术”研究领域。

The UK has set a legally binding target of net carbon zero by 2050 in every aspect of the economy and delivering sustainable and green solar electricity generation will be crucial in this transformation. Crystalline Si currently dominates the solar industry, representing approximately 95 % of the solar modules sold today. However, due to its low photon absorption coefficient and indirect bandgap, thicknesses up to 350 m are needed, making crystalline Si unsuitable for thin-film applications. Thin-film photovoltaic (PV) materials on flexible substrates will allow for the integration of solar energy conversion in buildings and infrastructure in urban environments, which is a key area of expansion in solar energy to meet required environmental targets. Cu2ZnSn(S,Se)4 (CZTSSe) is a non-toxic, inorganic thin-film material with desirable PV properties due to its tuneable direct bandgap between 1.0 - 1.5 eV and 20 % theoretical power conversion efficiency (PCE) under AM1.5G illumination. However, CZTSSe is currently limited by significant voltage losses, which have been linked to structural disorder including antisites defects, secondary phases, and point defect clusters, hindering the PCE. This PhD is part of a collaboration between the universities of Bristol, Northumbria and Loughborough on the SolPV project, funded by EPSRC, and industrial partners of Centre of Process Innovation, Johnson Matthey, BAE systems and M-Solv. The main purpose of this PhD is to perform interfacial engineering of the p-n junction between the CZTSSe absorber layer and buffer layer, using atomic layer deposition, to achieve record breaking efficiencies of greater than 15 %. CdS has been extensively used as a buffer layer for CZTSSe solar devices as it is an established buffer material for the most advanced technology of CuInxGa1-x(S,Se)2 (CIGS). Although CdS has worked as an efficient buffer layer in both CZTSSe and CIGS, Cd is toxic and cannot be released into the environment, therefore, a suitable replacement is required. In- and Zn-based oxysulfide alternatives will be investigated as possible replacements. Another aim of the project is to control crystallisation and composition of the absorber material and reduce the formation of detrimental defects, deep Sn trap states and carbon impurities by optimising the fabrication methodology. Bulk and surface composition and structure of the thin-films will be examined by electron microscopy techniques, Raman microscopy and Energy-Filtered Photoemission electron microscopy (EF-PEEM). EF-PEEM can provide surface electronic mapping of local effective work functions at the absorber-buffer junction, allowing for unique and vital electronic information. The focus of this research will be to confirm the PCE of CZTSSe solar cells will go beyond 15 %, while also using scalable manufacturing routes to ensure a smooth transition into industrial applications. This project falls within the EPSRC 'Solar Technology' research area.