The electronic-ionic mixed conducting nature of organometal halide perovskites (OHPs) necessitates the investigation of ion migration for complete understanding of the operation principle in OHP-based photovoltaic devices. Herein, the origins affecting the temporal transient of photovoltage/current profiles in (FAPbI3)0.83(MAPbBr3)0.17-based solar cells and their Cs-doped counterparts will be discussed (with FA standing for (NH2)2CH+, and MA for CH3NH3+, respectively). Rapid crystallization of OHPs by conventional antisolvent method has long been one of the most successful approach, but there are still room for the investigation of the impacts of thermal annealing on the OHPs’ characteristics: the microstructural evolution (and microstructure-related optical properties), mobile ionic species altering the energy landscape, and concomitant change of photocarrier kinetics in OHPs-based devices.[2,3] Frequency and time-dependent analyses, such as impedance spectroscopy and transient voltage/current measurements under controlled light/bias conditions, are used to understand the influence of ion migration on the photocarrier recombination in various timescales. Conductive atomic force microscopy further elaborates the effect of mobile ions on the electronic traps and the related photocurrent behaviours. These findings, all combined, will provide clues on the critical factors enabling the efficient and long-term stable OHP solar cells.
 R. A. Belisle, W. H. Nguyen, A. R. Bowring, P. Calado, X. Li, S. J. C. Irvine, M. D. McGehee, P. R. F. Barnes, and B. C. O’Regan, Energy Environ. Sci. 2017, 10, 192.
 T. Hwang, B. Lee, J. Kim, S. Lee, B. Gil, A. J. Yun, and B. Park, Adv. Mater. (accepted).
 T. Matsui, J.-Y. Seo, M. Saliba, S. M. Zakeeruddin, and M. Grätzel, Adv. Mater. 2017, 29, 1606258.