Effects of Frequency Dependence of the External Quantum Efficiency of Perovskite Solar Cells Sandheep Ravishankar, 1* Clara Aranda, 1 Pablo. P. Boix, 2 Juan A. Anta, 3 Juan Bisquert* 1 and Germà Garcia-Belmonte 1* 1 Institute of Advanced Materials (INAM), Universitat Jaume I, 12006 Castelló, Spain 2 Instituto de Ciencia Molecular (ICMol), Universitat de València, Catedrático José Beltrán, 2, 46980 Paterna, Spain 3 Department of Physical, Chemical and Natural Systems, University Pablo de Olavide, 41013, Sevilla, Spain Email: ravishan@uji.es, bisquert@uji.es , garciag@uji.es Abstract Perovskite solar cells are known to show very long response timescales, in the order of milliseconds to seconds. This generates considerable doubt over the validity of the measured external quantum efficiency and consequently the estimation of the short circuit current density. We observe a variation as high as 10% in the values of the EQE of perovskite solar cells for different optical chopper frequencies between 10 – 500 Hz, indicating a need to establish well-defined protocols of external quantum efficiency measurement. We also corroborate these values and obtain new insights regarding the working mechanisms of perovskite solar cells from intensity modulated photocurrent spectroscopy measurements, identifying the evolution of the external quantum efficiency over a range of frequencies, displaying a singular reduction at very low frequencies. This reduction in external quantum efficiency is ascribed to additional resistive contributions hindering charge extraction in the perovskite solar cell at short circuit conditions, which are delayed because of the concomitant large low-frequency capacitance.