柔性III-V多结太阳电池大尺寸制备的关键问题研究

The flexible solar cell offers excellent characteristics of high power to weight ratio and flexibility. These characteristics make flexible solar cells strong candidates for implementation in unmanned aerial vehicle, distributed photovoltaic power station and portable solar energy. Due to the high efficiency and high reliability of III-V multi-junction solar cell, developing the fabrication of flexible III-V photovoltaic device has attracted a broad attention around the world. The target of this project is to develop a kind of high efficiency flexible III-V solar cell by the epitaxial Lift-Off technique and thin film transfer. By adjusting the hetero-junction band structure, current-matched solar cell structure is grown by molecular beam epitaxy (MBE) using the approach of inverted metamorphic growth. Hetero-junctions like GaInP/AlInP are ultilized as Etching stop layer. The selective wet etching and epitaxial Lift-Off technique is combined to realize a rapid substrate removal. The thin film solar cell removed from their growth substrate is transferred to a copper handling and support foil by electroplating Cu. We will investigate the influence of device fabrication process on the performance of flexible III-V solar cell by comparing the efficiency of flexible solar cell with substrate based solar cell with the same structure. The investigation of flexible III-V solar cell with high efficiency and reliability will provide a powerful support for the energy demand in special area.

柔性III-V太阳电池由于其高效稳定特性在无人机、便携式、可穿戴电子产品的能源供给等诸多领域有着巨大需求。本项目针对柔性多结电池大尺寸制备的高效、稳定性等关键问题，利用分子束外延方法，基于双异质结构的腐蚀阻挡层设计，生长光电流匹配的倒置结构多结电池；将选择性湿法刻蚀技术和传统外延剥离技术结合，实现衬底快速腐蚀和剥离；基于电镀工艺，以柔性金属铜作为背支撑，实现大尺寸柔性电池的稳定制备；发展纳米尺度界面表征方法，研究柔性支撑与电池界面的微观缺陷、界面强度、串联电阻、载流子扩散等对电池效率的影响，实现太阳电池结构的综合设计提高。柔性、高效、稳定的大尺寸的III-V太阳电池的研发必将为未来能源需求提供必要的保障。

柔性Ⅲ-Ⅴ多结太阳电池因其高效、轻柔、稳定等优点，有望广泛应用于高空飞艇、临近空间大型无人机、商业航天等空间应用装置，以及新能源汽车、智能可穿戴装备等地面移动能源系统。本项目针对柔性高效III-V多结太阳电池制备中存在的大尺寸外延材料的剥离及转移、柔性衬底制备等技术难题展开研究，同时对多结太阳电池光电互易关系、失效机制等器件物理问题进行了系统分析。主要研究成果如下：.1. 分析了GaAs衬底失配生长的GaInP/GaAs/InGaAs三结太阳电池，表面原子力显微镜和横截面透射电子显微镜测试显示外延晶体质量良好。此外在三结太阳电池外延的基础上获得了1.96/1.55/1.17/0.83 eV AlGaInP/AlGaAs/InGaAs/InGaAs四结太阳电池，其中AlInGaAs组分步进缓冲层几乎将全部失配位错限制在内部界面使其不会穿透到有源区，两结InGaAs子电池的失配应力已基本弛豫。.2. 突破常规的柔性太阳电池制备方案，创新性地提出了电镀与低温键合相结合的薄膜外延层转移方案，使得柔性太阳电池的制备工艺缩减一半，柔性衬底和外延材料之间的残余应力大大降低，且电池更轻柔、良品率更高、更适合批量生产。采用该技术成功制备了4寸柔性三结太阳电池，光电转换效率达到34.68%，重量面密度为169 g/m2。该技术路线不受晶圆的尺寸限制，可以制备6寸、8寸甚至更大尺寸的晶圆，普遍适用于III-V多结太阳电池，有望以低成本实现大尺寸柔性多结太阳电池的量产。.3. 针对倒装直接生长的四结太阳电池存在的低短路电流密度但开路电压正常的这一关键问题，进行了四结太阳电池的失效分析。通过改用高纯三甲基铝源优化AlGaInP子电池材料的外延生长，获得了光电转换效率为34.9％、开路电压为3.53 V的四结太阳电池。针对多结叠层太阳电池的子电池电流密度-电压曲线无法直接测量的难点，采用外量子效率与不同注入电流密度电致发光之间的光电互易关系，计算了多结太阳电池的子电池电流密度-电压特性曲线。