低温生长Cu(InGa)Se_2薄膜吸收层的掺钠工艺研究

Research on sodium incorporation methods of growing Cu(In-Ga)Se_2 thin film by low-temperature deposition

在柔性聚酰亚胺衬底上低温制备Cu(In,Ga)Se_2薄膜太阳能电池,Na的掺入会改善电池特性,但不同的掺Na工艺对Cu(In,Ga)Se_2薄膜和器件特性的改善机理不同.本实验通过对比前掺NaF和后掺NaF工艺发现,在前掺Na工艺下,由于Na始终存在于Cu(In,Ga)Se_2薄膜生长过程中,Na存在于多晶Cu(In,Ga)Se_2薄膜晶界处,起到了扩散势垒的作用,导致晶粒细碎、加剧两相分离,同时减小了施主缺陷的形成概率;而在后掺Na工艺下,掺入的Na对薄膜的结构及生长不产生影响,仅仅起到了钝化施主缺陷、改善薄膜缺陷态的作用.同时,研究表明,后掺Na工艺中,NaF必须依靠外界能量辅助才能扩散进Cu(In,Ga)Se_2内部,实验结果证实,只有衬底温度达到350℃以上时,掺入的NaF才能较好地改善薄膜特性.最终经掺Na工艺的优化,得到低温工艺制备的柔性聚酰亚胺衬底器件效率达10.4%.

Sodium is proved to be able to improve the performance of Cu（In,Ga）Se2 solar cell grown on flexible polyimide substrate by a low-temperature deposition. Different sodium incorporation methods affect the film in different ways. Comparing the deposition of a NaF precursor with post deposition NaF treatment, different mechanisms can be found. In NaF precursor approach, Na is available during the Cu（In,Ga）Se2 growth and acts as a surfactant at the grain boundary which adds up an energy barrier for adatom to across. Thus, a small grain size as well as double-peak reflection pattern can be observed and the formation probability of donor defects is reduced. In post deposition NaF treatment, incorporation of NaF does not affect the growth and microstructure but passivates donor defects in the Cu（In,Ga）Se2 film. Moreover, according to the experimental results, external energy assistance is necessary during NaF incorporation through post deposition treatment. It is verified that Na incorporation is able to improve the properties of the film effectively when substrate temperature reaches above 350 ℃. Finally, the conversion efficiency of flexible Cu（In,Ga）Se2 thin film solar cell on polyimide substrate is achieved to be 10.4% by optimizing the sodium incorporation.