聚合物薄膜/硅界面钝化机制及其在光伏技术中的应用

The power conversion efficiency of crystalline silicon (c-Si) solar cell is being close to its theoretical limit. Further research work will focus on reducing the costs of device fabrication while maintaining its high efficiency. A passivation scheme for the suppression of surface/interface recombination is the core of high-efficiency c-Si solar cells. The conventional passivation schemes, such as SiO2, Al2O3 and hydrogenated amorphous silicon (a-Si:H), have been developed very maturely. However, they require high-vacuum and/or high-temperature process, which hinders efforts to further reduce the costs of device fabrication.. Organic materials and their fabrication process possess potential low-cost advantage. In the applicant’s previous work, a polystyrene sulfonic acid (PSS) polymer thin film, which was fabricated at a low-temperature and vacuum-free condition, was found to achieve an excellent passivation effect. In the present project, a physical mechanism for PSS/Si interface passivation properties and its application in the photovoltaic device, will be deeply investigated, including: 1) aberration-corrected transmission electron microscopy (ACTEM) is employed to obtain the grafting process of PSS molecule on Si surface, and the interfacial micrograph of PSS/Si heterojunction, while the first-principle calculations is employed to unveil the origin of passivation together; 2) the energy band lineup and carrier transport properties of organic-inorganic hybrid heterojunction will be studied and the evolution of the passivation over time will be revealed; 3) this polymer passivation technology and its operating mechanism are to be introduced into interdigitated back contact (IBC) solar cells; the internal connection between passivation mechanisms of the PSS/c-Si interface and photovoltaic properties of the solar cell device, will be studied. It is of great significance to achieve the present project for boosting the development of the new low-cost passivation technology in the near future.

硅太阳电池能量转换效率的发展已接近理论极限，下一步的研究焦点将逐渐集中在如何以低成本实现高效率。其核心技术—表/界面钝化材料(如氧化硅、氧化铝和非晶硅薄膜)的制备，需要高温工艺或高真空装备，严重阻碍了器件成本的降低。申请人前期工作发现聚苯乙烯磺酸(PSS)薄膜可以在低温非真空条件下实现高质量的钝化效果。本项目拟进一步研究PSS薄膜的钝化机制及其在光伏器件中的应用：①采用球差校正透射电子显微镜获取PSS/Si界面原子结合情况、界面微观图像等信息，并结合第一性原理计算揭示钝化的物理本源；②分析聚合物薄膜/硅异质结能带结构和载流子输运特性，研究钝化效果的时间演变规律；③将聚合物钝化应用到叉指背接触(IBC)太阳电池前表面，研究带有聚合物钝化层的IBC电池的光伏特性，探讨这种钝化技术在太阳电池器件中的运行机理和性能调控机制。本项目的完成对促进未来新型低成本钝化技术的发展具有重要意义。

硅太阳电池能量转换效率的发展已接近理论极限，下一步的研究焦点将逐渐集中在如何以低成本实现高效率。其核心技术—表/界面钝化材料(如氧化硅、氧化铝和非晶硅薄膜)的制备，需要高温工艺或高真空装备，严重阻碍了器件成本的降低。申请人前期工作发现聚苯乙烯磺酸(PSS)薄膜可以在低温非真空条件下实现高质量的钝化效果。. 围绕这一新发现的非真空钝化技术，本项目进一步研究了聚合物PSS薄膜/硅界面钝化的深层次物理机制，包括界面处有机分子与硅表面原子的嫁接机制、有机-无机异质结能带结构与载流子的输运特性等问题；并将其应用到叉指背接触(IBC)太阳电池前表面，研究了带有聚合物钝化层的IBC电池的光伏特性，探讨了这种钝化技术在太阳电池器件中的运行机理和性能调控机制。取得主要结果及结论如下：. 1. 精准地获得了界面微观图像、原子价态、嫁接方式等结果，弄清了新型钝化技术的物理机制，在两种非铁电材料(聚合物薄膜PSS和单晶硅Si)的界面发现了可翻转的界面偶极子和有机-无机界面铁电现象，确立了“电化学铁电钝化”的新型钝化机制。. 2. 研究了钝化的功能本源，发现该技术的材料体系为磺酸基薄膜材料。. 3. 掌握了聚合物薄膜/硅异质结能带结构和载流子输运特性，发明了“导电钝化接触”的新型光伏器件构造，采用这一构造，不再像传统太阳电池那样需要真空介电薄膜和高温掺杂两种以上的材料才能实现钝化和载流子选择传输的双重功能，而是仅用单层复合薄膜就可以同时实现两种物理效果。这为简化硅太阳电池制程、降低制造成本提供了全新的技术思路。该成果入选能源领域顶级刊物《Adv. Energy Mater.》封面文章，被刊登在基金委主办期刊《Science Foundation in China》(Vol. 28, No. 2, 2020)。. 4. 掌握了聚合物钝化在太阳电池器件中的运行机理、性能调控机制以及效率损失途径，获得了22.4%的电池效率。