氧化钛/晶体硅钝化接触结构的制备及其在非掺杂电荷选择性异质结太阳电池中的应用研究

Dopant-free carriers-selective crystalline silicon (c-Si) heterojunction solar cells have become an important alternative technology for high-efficiency and low-cost silicon solar cells, due to its simple process and large potential for efficiency improvement. Also, the nature of the low temperature process prevents the warping phenomena of the thin c-Si wafers in production, consistent with the trends of using thinner wafers. This project fabricates TiOx thin films with high electron selectivity, high performance of passivation and low contact resistance, using a relatively simple oxidation process from thin Ti films. The structures/defects and properties of TiOx and c-Si/ TiOx heterocontact are investigated comprehensively and the correlation among the TiOx process, TiOx structures/properties, c-Si/ TiOx heterocontacts and solar cells are established. Also, the Si surface is chemically treated to modify the interface properties, which will influence the band bending of n-Si/ TiOx heterocontact and the carrier separation and collection. In addition, the conductivity and work function of TiOx is manipulated by doping of metals with low work function to achieve more effective carrier collection and higher built-in electrical field for the devices. From the efforts stated above, a general empirical principle that could help to improve the interface quality, built-in electrical field intensity and carrier collection efficiency of the “dopant-free high electron selectivity Si-based heterocontacts” will be eventually developed, which will give a sufficient guidance to the Si heterojunction solar cells with higher performance and lower cost, even the development of the carrier-selective interface layers in the Si based dual junction solar cells.

非掺杂电荷选择性晶体硅异质结太阳电池摒弃了传统的高温扩散掺杂工艺，凭借其制备工艺简单，转换效率提升空间大等优点，成为晶硅电池高效化和低成本化的一个重要的技术路线。另外，其低温工艺不会导致薄膜硅片翘曲，与产业的硅片薄膜化趋势也兼容。本项目提出采用简单的新型金属薄膜低温氧化法制备工艺，制备出具有高电子选择性且具有良好界面钝化和接触性能的TiOx功能薄膜，研究制备工艺对TiOx结构/缺陷，和性能的影响，考察影响异质结钝化接触特性和器件性能的物理规律。进一步，利用界面修饰处理、TiOx杂质掺杂等措施改善n-Si/TiOx异质结的综合性能。通过上述的研究，归纳出对n-Si/TiOx异质结内建电场、界面质量、电荷提取这三方面同步提升的界面设计准则，指导非掺杂电荷选择性硅异质结太阳能电池的研究和开发。另外，本研究的顺利开展对硅基双结太阳电池中的电荷选择传输层的开发也具有借鉴意义。

非掺杂电荷选择性晶体硅异质结太阳电池摒弃了传统的高温扩散掺杂工艺，凭借其制备工艺简单，转换效率提升空间大等优点，成为晶硅电池高效化和低成本化的一个重要的技术路线。另外，其低温工艺不会导致薄膜硅片翘曲，与产业的硅片薄膜化趋势也兼容。本项目采用低温工艺制备氧化钛薄膜，通过在TiOx与n-Si接触界面形成高质量Ti-O-Si键来实现化学钝化的作用，制备出效率为18.8%的非掺杂异质结晶硅电池；通过氟掺杂技术，提升氧化钛电子选择性钝化层钝化和接触质量，使表面复合速度降至～10 cm/s和接触电阻率降至～20 mΩ·cm2。进一步通过IBC结构，制备出效率超过20%的器件。通过本项目的执行，将有助于加深对这种新型非掺杂异质结太阳能电池的工作机制的理解和认识，明确材料改性、界面修饰、器件结构设计、能带调控等优化方向，推动非掺杂电荷选择传输器件效率的大幅提升。同时，这些针对异质结电池界面接触特性的共性研究成果，为构建高效的非掺杂异质结电池积累经验，为课题组TOPCon等项目开发，奠定了坚实的基础。