Proceedings of 13th Conference on Hybrid and Organic Photovoltaics (HOPV21)
Publication date: 11th May 2021
A precise control over the layer thickness and the composition is a prerequisite for the fabrication of perovskite solar cells. Researchers often use reference samples and a plethora of characterization methods for that purpose [1, 2, 3, 4, 5]. In this study, we show that information on thickness and stoichiometry of the absorber layer are accessible using only reflection measurements of perovskite solar cells, even if only limited optical reference data is at hand. This is useful e.g. for the retrospective analysis of perovskite solar cells for which no reference samples exist, or if resources for additional samples or measurements are scarce. Additionally, some steps during cell processing can influence the perovskite layer, such that the usage of reference samples is not always feasible.
From interferences in the lower wavelength region, in the case of our solar cells from 300 to 500 nm, we can deduct the thickness of the TCO and the contact layers of the front side of the solar cell by fitting a simple optical model to the reflection data. The higher wavelength interferences from 500 to 800 nm serve to determine the thickness of the perovskite and back contact layers. A higher than expected reflection in this wavelength regime is indicative of a non-stoichiometric (e.g. with excess PbI2) or phase-separated/non-converted perovskite layer. To quantitatively describe the amount of excess material or phase-separation/non-conversion we use an effective medium layer consisting of both perovskite and the excess material. This allows to quantify the severity of either phase-separation/non-conversion or non-stoichiometry and can be used to optimize the perovskite layer.
Since only a solar cell reflection measurement is needed, this procedure allows for a fast analysis of several important parameters of a perovskite solar cell, without employing an extensive set of measurement tools.
The authors would like to thank Verena Barnscheidt, Yevgeniya Larionova, Tobias Neubert, David Sylla, Verena Steckenreiter, Jessica Strey and Mircea Turcu for sample processing and measurements.
Funding for this work was provided by the German Federal Ministry for Economic Affairs and Energy under grant numbers 03EE1017B and 03EE1056A (projects P3T and 27+6) as well as by the Federal State of Lower Saxony.
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