A Theoretical Perspective on Transient Photovoltage and Charge Extraction Techniques

TL;DR

This paper reviews and extends the theory of transient photovoltage and charge extraction techniques, demonstrating their application in accurately determining recombination dynamics and carrier properties in thin-film solar cells through simulations and experiments.

Contribution

It provides a theoretical framework for TPV and CE, identifying regimes for accurate measurements and emphasizing the importance of varied light intensities for reliable recombination analysis.

Findings

Identified regimes for accurate lifetime and carrier density determination.

Demonstrated the necessity of wide steady-state light intensity range.

Validated theoretical insights with simulations and experiments.

Abstract

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.