Quantification of electron accumulation at grain boundaries in perovskite polycrystalline films by correlative infrared-spectroscopic nanoimaging and Kelvin probe force microscopy oleh Ting-Xiao Qin, En-Ming You, Mao-Xin Zhang, Peng Zheng, Xiao-Feng Huang, Song-Yuan Ding, Bing-Wei Mao, Zhong-Qun Tian