Abstract：
Polyvinyl pyrrolidone is blended in PbI2 with varied concentration, so as to study the coarsening dynamics of perovskite during the two-step growth method. It is observed that polyvinyl pyrrolidone hinders the crystallization of PbI2 and helps to form a more amorphous PbI2 matrix, which then improves perovskite crystallization. As the blending concentration increases from 0 to 2 mM, average crystallite/grain size of perovskite increases from 40.29 nm/0.79 µm to 84.35 nm/1.02 µm while surface fluctuation decreases slightly from 25.64 to 23.96 nm. The observations are caused by the \"confinement effect\" brought by polyvinyl pyrrolidone on PbI2 . Elevating blending concentration of polyvinyl pyrrolidone results in smaller PbI2 crystallites and more amorphous PbI2 matrix, thus reducing the diffusion/reaction barrier between PbI2 and organic salt and favoring perovskite crystallization. As blending concentration increases from 0 to 2 mM, the device efficiency rises from 19.76 (± 0.60) % to 20.50 (± 0.89) %, with the optimized value up to 22.05%, which is further improved to 24.48% after n-Octylammonium iodide (OAI)-basing surface modification. The study enlarges the scope of \"confinement effect\" brought by polymer molecules, which is beneficial for efficient and stable perovskite solar cell fabrication.
摘要：
聚乙烯吡咯烷酮混合在不同浓度的PbI2中，从而研究两步生长法过程中钙钛矿的粗化动力学。观察到聚乙烯吡咯烷酮阻碍了PbI2的结晶，并有助于形成更无定形的PbI2基质，然后改善钙钛矿结晶。随着混合浓度从0增加到2mM，钙钛矿的平均微晶/晶粒尺寸从40.29nm/0.79µm增加到84.35nm/1.02µm，而表面波动从25.64nm略微减小到23.96nm。观察结果是由聚乙烯吡咯烷酮对PbI2带来的“限制效应”引起的。提高聚乙烯吡咯烷酮的混合浓度导致更小的PbI2微晶和更无定形的PbI2基质，因此减少了PbI2和有机盐之间的扩散/反应障碍，有利于钙钛矿结晶。随着混合浓度从0增加到2mM，器件效率从19.76(±0.60)%上升到20.50(±0.89)%,优化值高达22.05%，经过正辛基碘化铵（OAI）的表面改性，进一步提高到24.48％。该研究扩大了聚合物分子带来的“约束效应”的范围，有利于高效稳定的钙钛矿太阳能电池的制造。
