大气环境中溶剂添加剂对制备钙钛矿薄膜的影响

Solvent engineering during the preparation of perovskite thin films in air

钙钛矿太阳能电池中有机-无机杂化钙钛矿薄膜的品质很大程度上决定了其器件效率。作为简单有效的制备方法,近几年一步溶液旋涂法不断改进工艺,迅速广泛应用于高质量钙钛矿薄膜的制备,其中在前驱体溶液中添加二甲基亚砜(Dimethyl sulfoxide,DMSO)以及旋涂过程中滴加反溶剂被普遍认为是行之有效的手段,可以大幅提升钙钛矿的结晶质量,获得均匀致密的薄膜。本文通过控制钙钛矿薄膜制备过程中前驱体溶液DMSO和旋涂过程中反溶剂乙醚的添加与否,在大气环境制备了4种不同的薄膜样品,结合扫描电子显微镜、同步辐射掠入射X射线衍射以及器件效率测试等研究了薄膜的表面形貌、结晶性与基于它们制备的器件性能的差异,探究了DMSO和乙醚两种添加剂对钙钛矿成膜的影响、机制及其构效关系。同时,进一步采用同步辐射掠入射X射线衍射研究4种薄膜样品在空气环境下原位加热过程中钙钛矿结晶、退化以及期间晶格结构的演变,发现前驱体溶液中加入DMSO对于钙钛矿结构形成具有延迟作用,而反溶剂乙醚的滴加则对薄膜形貌、结晶、晶面取向乃至器件光电转换效率具有显著的提升,并且其钙钛矿结构具有较好热稳定性。本文的发现将为改善钙钛矿薄膜制备工艺以进一步提升其器件光电转换效率与稳定性提供一定的实验依据。

[Background] The quality of the organolead halide layers in perovskite solar cells （PSCs） largely determines the performances of their device such as power conversion efficiency （PCE）. Among a variety of preparation methods developed, one step solution spin coating is currently the most popular but a simple and effective preparation technique to fabricate high quality perovskite thin films. [Purpose] The quality of the perovskite films depends strongly on the detailed preparation procedures. This paper aims to study the influence of solvent engineering during the preparation of the perovskite thin films especially on their crystallinity and thermal degradation. [Methods] There were four different perovskite films prepared in this study： one without any solvent engineering, one with dimethyl sulphoxide （DMSO） added in the precursor solution, one with antisolvent treatment by using ether, and one with both DMSO added and antisolvent treatment. The morphology and crystallinity of the thin films were studied by scanning electron microscopy （SEM） and synchrotron-based grazing incidence X-ray diffraction （GIXRD）, respectively. The PSC performances were characterized by current density-voltage test. Moreover, the evolutions of crystallinity of the fabricated perovskite films during an in-situ heating experiment were monitored by GIXRD in air to study their crystallization and degradation. [Results] DMSO has little effects on the surface morphology and device performance, but postpones the perovskite crystallization process. The antisolvent promotes forming uniform dense films leading to high performance PSC and improves thermal structural stability. [Conclusion] In one step spin coating, high quality thin films can be obtained quickly and effectively by an antisolvent treatment.