  Transient photovoltage (TPV) is a technique frequently used to determine
charge carrier lifetimes in thin-film solar cells such as organic, dye
sensitized and perovskite solar cells. As this lifetime is often incident light
intensity dependent, its relevance to understanding the intrinsic properties of
a photoactive material system as a material or device figure of merit has been
questioned. To extract complete information on recombination dynamics, the TPV
measurements are often performed in conjunction with charge extraction (CE)
measurements, employed to determine the photo-generated charge carrier density
and thereby the recombination rate constant and its order. In this
communication, the underlying theory of TPV and CE is reviewed and expanded.
Our theoretical findings are further solidified by numerical simulations and
experiments on organic solar cells. We identify regimes of the open-circuit
voltage within which accurate lifetimes and carrier densities can be determined
with TPV and CE experiments. A wide range of steady-state light intensities is
required in performing these experiments in order to identify their 'working
dynamic range' from which the recombination kinetics in thin-film solar cells
can be determined.
