前驱体混合比例对CH3NH3PbI3钙钛矿薄膜微观结构及光伏器件性能的影响

Influences of precursor ratio on microstructure of perovskite CH_3NH_3PbI_3 film and photoelectric conversion properties of perovskite solar cell

有机-无机杂化钙钛矿太阳能电池具有优异的光电性质、简单的制备工艺等优点,短短几年内其最高光电转换效率已超过21%,成为高效太阳能电池非常有前景的研发热点。一步溶液旋涂法是目前CH_3NH_3PbI_3等钙钛矿材料使用最广泛、最简便的制备方法。在制备中前驱体混合比例尤为关键,在一定程度上决定着薄膜结晶质量、表面形貌以及表面化学成分,并对最终器件效率产生重要影响。利用同步辐射掠入射X射线衍射(Grazing incidence X-ray diffraction,GIXRD)、扫描电子显微镜(Scanning electron microscopy,SEM)和X射线光电子能谱(X-ray photoelectron spectroscopy,XPS)系统地研究了不同前驱体混合比例对CH3NH3Pb I3薄膜的结晶机理、表面形貌及化学组分的影响。研究结果表明,增加CH_3NH_3I的混合比例虽然会增强钙钛矿晶体的织构现象、提升钙钛矿薄膜表面覆盖率,但器件效率大幅下降。XPS结果表明,钙钛矿薄膜中前驱体碘甲胺和碘化铅反应不充分,残余驱体聚集在薄膜表面,这将导致器件载流子传输层/钙钛矿薄膜界面处载流子收集能力的降低,进而导致器件性能的降低。研究结果将为深入理解前驱体比例对高质量钙钛矿薄膜制备以及钙钛矿太阳能电池的光电转换性能和稳定性的影响机制提供必要的实验依据和指导。

Background： Organometal perovskite solar cells （PSCs） have attracted widespread consideration due to their conversion efficiency exceeding 20%. Because their outstanding photoelectric properties and their preparation process are often simple, among which one-step process has been most widely used. Purpose： This study aims to determine whether the mixing ratio of the precursor CH3NHaI and PbI2 is particularly critical for the preparation of CH3NHaPbI3 film, and thus influences the performance of PSCs. Methods： Synchrotron-based grazing incidenceX-ray diffraction （GIXRD）, scanning electron microscopy （SEM）, and X-ray photoelectron spectroscopy （XPS） were employed to study the microstructure, surface morphology, chemical compositions of CH3NH3PbI3 film prepared using one-step process with different precursor （CH3NH3I and PbI2） ratios. Results： Results of GIXRD showed that the increase of CH3NH3I portion would reduce the degree of perovskite crystallinity with CH3NH3I and few PbI2 residue but enhance their preferential orientation along the out-of-plane direction, especially that of the perovskite （110） plane. In addition, a higher proportion of precursor CH3NH3I improved the surface morphology of the perovskite film with a better coverage as revealed by SEM. On the other hand, XPS results demonstrated that the increasing CH3NH3I portion caused Pb and I to enrich on the surface. Conclusion： The present study explored the influence of the mixing ratios of the precursors on the microstructure, surface morphology of perovskite films, as well as the device performance, which would provide experimental basis and guidance for preparing perovskite films for high performance perovskite solar cells with improved stability.