高效率柔性CIGS薄膜太阳电池生长机理研究

CIGS thin film solar cell on polyimide (PI) foils with high efficiency beyond 20% has been achievement by the co-evaporation process in low substrate temperature. However, the mechanism contributed to the improved performance of CIGS films and solar cell has not been made clear completely. In this study, the growth mechanism of CIGS films on PI foils deposited by co-evaporation process on low temperature will be investigated systematically. It is developed from two aspects, i.e. the chemical reaction path and the physical process during the growth periode of CIGS film. Firstly, the physical process of the growth of CIGS films, like the change of crystalline state and the diffusion mechanism, will be investigated by analyse the character of the films.The chemical reaction path of the growth of CIGS films is confirmed basing on the study of those compounds and thermodynamics theory and calculation results. Secondly, the influence of K-doping on the structrual properties and compostion of CIGS film surface, and the electral properties such as minority carrier liftime, formation of defects, is study in detail. At last, the model of the growth of CIGS films will be established. This research will be contribute to gain the key technique for depositing CIGS films with high quality by the co-evaporation process on low temperature, and provide experiment and theory foundation for developing the high efficiency CIGS thin film solar cells on PI foils.

目前，采用低温蒸发工艺在聚酰亚胺衬底（PI）上制备CIGS薄膜太阳电池的光电转换效率已超过20%。然而，显著改善CIGS吸收层性质和电池性能的根本原因还有待研究。本项目从CIGS薄膜形成的化学反应路径和物理过程两方面，对低温蒸发工艺沉积CIGS薄膜的生长机理进行研究。在此基础上，研究K原子改善CIGS薄膜电学特性的作用机理。首先，通过分析不同工艺条件下硒化物薄膜性质的变化，研究薄膜结晶过程，元素扩散机制等物理过程，并结合化学反应热力学理论，研究CIGS薄膜形成的化学反应路径。然后，通过分析后掺入Na和K后，吸收层表面结构和元素分布，以及少子寿命、缺陷形成及分布的影响。在此基础上建立低温蒸发工艺制备CIGS薄膜的生长模型。本项目的开展将有助于从薄膜生长机理层面上认识低温蒸发工艺，掌握在PI衬底上获得高质量CIGS吸收层的关键技术，为我国研发高效率PI衬底CIGS薄膜太阳电池提供理论和实验基础

柔性CIGS薄膜太阳电池，因为其具有高光电转换效率、高质量比功率、适合大规模卷对卷批产等优点，未来在建筑光伏一体化、空间飞行器、飞艇等方面具有广泛应用前景。本项目从CIGS薄膜形成的化学反应路径和物理过程两方面，对低温蒸发工艺沉积CIGS薄膜的生长机理进行了研究，并研究了K原子改善CIGS薄膜及电池的作用机理。研究发现，生长温度和Cu、In、Ga的蒸发顺序对薄膜生长过程具有重要影响，Tsub=450℃对CIGS薄膜生长反应路径是一个关键温度转折点，它决定了形成CIGS薄膜的不同反应路径和Ga、In的互扩散机制。采用顺序蒸发Ga-In-Cu工艺，生长温度在450-500℃，在足够的Se饱和蒸汽压下，R19与R23形成链式反应，在此过程中，Ga、In借助化学反应动力学过程完成互扩散，得到结晶质量很好的、具有合适带隙梯度的CIGS薄膜。在此基础上通过系统研究，得到适合低温生长（450℃-500℃）高质量CIGS吸收层的反应路径为（R1、R10）—（R9、R17、R19）—（R21、R23）—R24—R25，并建立的低温生长CIGS吸收层的五步生长模型。在CIGS薄膜中掺入KF，K对于Se颗粒具有再裂解作用，相当于提高了反应过程中Se的化学反应活性，提高了生长CIGS薄膜的相关化学反应的速率或是部分改变了反应路径。但是共蒸发过程中掺入KF也会影响CIGS薄膜生长的动力学过程，引入深能级缺陷，导致电池性能降低。后掺杂KF并经过退火工艺，K主要作用是钝化CIGS表面和异质结界面，降低界面复合速率，提高薄膜的有效p型掺杂，达到提高电池性能的效果。基于上述研究，对柔性CIGS薄膜太阳电池工艺进行了优化，研制出面积250cm2的PI衬底CIGS薄膜太阳电池组件效率达到11.3%。