Abstract
The development of organic-inorganic lead halide perovskites with very large efficiency requires us to understand the operation of the solar cell. This class of semiconductors presents remarkable bulk electronic and optical properties, but the contacts to the device are a key aspect of the operation and show important dynamic interactions. We provide an interpretation of capacitances as a function of frequency both in dark and under light, and we discuss the meaning of resistances and how they are primarily related to the operation of contacts in many cases. The capacitance reveals a very large charge accumulation at the electron contact, which has a great impact in the cell measurements, both in photovoltage decays, recombination, and hysteresis. We present the surface polarization model that gives insight and quantitative description of current-voltage dynamic hysteresis and impedance spectroscopy loops. We develop a global view of the formation of photovoltage and the kinetic processes governing the operation of the solar cell, providing a suitable unified explanation to the many strange observations reported in the last few years.