Insights into the hole transport properties of LiTFSI-doped spiro-OMeTAD films through impedance spectroscopy. - Li, Bixin; Zhang, Shiyang; Xia, Fei; Huang, Yongliang; Ran, Xueqin; Xia, Yingdong; Chen, Yonghua; Huang, Wei (Journal of Applied Physics, 2020)