以PECVD制备的应用在免掺杂钝化接触光伏电池中的Nb2O5的钝化和电子选择性的研究

The key to further development of silicon-based passivated contact photovoltaic cells lies in the search of novel dopant-free passivation and carrier selective materials. Unfortunately, no material that can simultaneously provide sufficient passivation and electron selectivity on silicon substrate is ever reported. Although Nb2O5 has an ideal energy band structure and passivation quality to fulfil the above-mentioned role, in-depth study on silicon substrate is still lacking, and the reported properties are far from optimum. So far, no application in functional dopant-free passivated contact solar cell is ever demonstrated. This project intends to develop a preparation method for novel Nb2O5 material on n-type silicon substrate using plasma-enhanced chemical vapor deposition technique. Material morphology and stoichiometry will be controlled through the selection of suitable deposition precursors and the adjustment of deposition parameters. Silicon sub-oxide layer grown on wafer surface as a result of post-deposition annealing will be studied for its passivation and electron transport mechanisms. Through the investigation of interface fixed charge originated from different oxygen vacancy and Nb coordination conditions, the trade off between chemical and field effect passivation, as well as the influence of interfacial p++ inversion layer on electron selectivity will be discussed. Electron conductivity will be optimized through the control and study of localized traps near Nb2O5 conduction band. This project will establish PECVD preparation technique for novel high-quality Nb2O5 film and optimize its key passivation and electron selective properties, thus providing strong material support for the development of dopant-free passivated contact solar cells.

进一步发展硅基钝化接触光伏电池的核心在于寻找新型免掺杂钝化载流子选择材料。目前报道过的材料并没有一种可以同时满足在硅衬底上的钝化和电子选择性。Nb2O5的能带结构和钝化性质虽然适合作为上述用途，但在硅基衬底上尚未被深入研究，性能也未达到最佳，在免掺杂钝化接触电池中的应用更是空白。本项目拟研发以PECVD在n型硅基衬底上制备该新型材料的技术，选择合适的反应前驱物，并通过调整制备参数控制材料的晶态和化学计量；通过研究退火后在硅表面形成的氧化硅明确化学钝化以及界面电子传输的机制；通过研究不同氧缺位和Nb配位情况下的界面固定电荷探讨场效应和化学钝化的相互制约以及界面p++反转层对电子选择性的影响；通过控制并研究导带能级附近的局部陷阱优化材料的导电性。本项目将建立高质量新型Nb2O5的PECVD制备技术，优化关键钝化和电子选择性质，为免掺杂钝化接触电池的发展提供有力的材料支持。

本项目研究了五氧化二铌（Nb2O5）在高效异质结光伏电池上的钝化和电子传输性能并做了一定的优化。研究首先针对传统异质结电池作了制备流程上的优化，即使用氢等离子体刻蚀（HPE）工艺代替了传统的氢氟酸（HF）清洗去除制绒硅片表面的本征氧化物，并在器件上实现了光电转换效率接近1%abs的提升；其次，我们利用PECVD工艺制备了Nb2O5用以替代传统电池上的非晶硅钝化层和n型多晶硅电子传输层，该替换虽然在一定程度上降低了电池效率，但由于将原先的钝化/电场层变为了单一的免掺杂钝化导电层，因此在简化电池的制备工艺，同时保持较高的转换效率方面做出了贡献。