Prof. Xu Pan and Dr. Jiajiu Ye from the Institute of Solid-State Physics (ISSP), Hefei Institutes of Physical Science (HIPS), Chinese Academy of Sciences and their cooperators Prof. Park Nam Gyu from the Sungkyunkwan University and Prof. Songyuan Dai from North China Electric Power University, investigated the non-uniformity of perovskite thin films along the vertical direction and analyzed the cause for this non-uniformity and its potential impact on the perovskite solar cells device.