基于掺硼直拉单晶硅片的Al-BSF和PERC太阳电池光衰及其抑制的基础研究

The development of Al-BSF and PERC solar cells based on boron-doped Czochralski silicon (Cz-Si) wafers has been greatly limited by their LID (light induced degradation) problems, which is to a large extent related to some basic scientific issues about LID of these two solar cells being unsolved until now, for example, what are the factors that induce the LID of these two solar cells? And what is the proportion of their respective contribution to the LID of these two solar cells? To solve these two scientific problems, we will use the latest-developed regeneration technology to eliminate boron-oxygen defects induced LID, and use atomic layer deposition (ALD) of Al2O3 and subsequent annealing to eliminate the transition metal impurities in Cz-Si wafers and the related LID, and decouple these LID factors and their respective contributions to the LID of these two solar cells by skillfully designing the experiment according to the characteristics of various possible LID factors. On this basis, find a method to fully eliminate the LID of these two solar cells. It is expected that the research results will be of great reference value to deepen the knowledge and find a permanent solution to the LID problems of Al-BSF and PERC solar cells based on boron-doped Cz-Si wafers.

由掺硼直拉单晶硅片制备的铝背场（Al-BSF）电池和PERC （Passivated Emitter and Rear Cell）电池的光衰（LID）问题极大地限制了它们的发展，这与与此有关的一些基础科学问题仍未得到很好的解决有关，譬如引起这两种电池LID的因素有哪些？它们对电池LID贡献的比例是多少？针对这两个科学问题，本项目将利用最新发展出的复原（regeneration）技术来消除硼-氧缺陷引起的LID，利用原子层沉积（ALD）Al2O3并退火来除去硅片内的过渡金属杂质进而消除金属杂质引起的LID。根据可能存在的各种光衰的特点，通过巧妙设计实验来分离引起这两种电池LID的因素及其对电池LID贡献的比例。在此基础上，寻求彻底消除这两种电池LID的方法。预计本项目研究成果对于进一步认识和寻求基于掺硼直拉单晶硅片的Al-BSF 电池和PERC 电池的LID问题的彻底解决具有重要的参考价值。

通过研究一根产业化太阳能级掺硼直拉单晶硅（Cz-Si）棒上不同位置硅片制备的产业化Al-BSF电池和PERC电池的原位光衰以及复原规律，基本澄清了硅片内不同杂质在两种电池上引起的光衰及贡献的比例。无论是Al-BSF电池还是PERC电池，电池的光衰都是由B-O缺陷起主导作用，Fe-B对的分解起次要作用，而太阳能级Cz-Si中铜和镍的含量较低，且本身为快扩散杂质，能够很好地被磷扩散吸杂去除，即使不能完全去除，与铜和镍有关的复合中心也能够被带有含氢钝化膜（PECVD-SiNx:H）的烧结过程很好地氢钝化，几乎不会对电池的光衰产生影响。在45℃、1sun、12h的光衰条件下，B-O缺陷和Fe-B对的分解总共能够在未经抗光衰处理的PERC电池和Al-BSF电池上引起的效率衰减率分别为4.43%—5.56%（相对值）之间和2.75%—3.8%（相对值）之间，其中Fe-B对的分解单独在两种电池上引起的效率衰减率分别为0.33%—1.75%（相对值）和0.42% —1.23%（相对值）之间。在45℃、1sun的光衰条件下，Fe-B对的分解引起的光衰在3h内可达到饱和，而B-O缺陷引起的光衰则需要9-12h才能达到饱和。PERC电池光衰到底和复原达到饱和所需的时间均短于Al-BSF电池，前者所需的时间分别为9h和18h左右，而后者所需的时间分别为12h和20h左右。100℃、1sun、24h的复原处理基本可以完全钝化两种电池内部的B-O缺陷，但不能钝化与Fe有关的缺陷。在我们的光衰（45℃、1sun、12h）和复原（100℃、1sun、24h）实验条件下，两种电池都不存在LeTID现象。