Analysis and Quantification of Ionic Charge Carriers in Perovskite Solar Cells
Andreas Schiller a b, Sandra Jenatsch a, Stijn Lammar c, Renàn Escalante d, Balthasar Blülle a, Antonio J. Riquelme d, Gerko Oskam d, Juan A. Anta d, Beat Ruhstaller a b
a Fluxim AG, 8400 Winterthur, Switzerland
b ZHAW – Institute of Computational Physics, 8401 Winterthur, Switzerland
c Imec, imo-imomec, Thin Film PV Technology – partner in Solliance, Thor Park 8320, 3600 Genk, Belgium
d Department of Physical, Chemical and Natural Systems, (Univ. Pablo de Olavide), Sevilla, Spain
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP23)
Kobe, Japan, 2023 January 22nd - 24th
Organizers: Seigo Ito, Hideo Ohkita and Atsushi Wakamiya
Oral, Sandra Jenatsch, presentation 019
Publication date: 21st November 2022

Several short and long-term effects in perovskite solar cells, such as the hysteresis in the current-voltage (IV) curve,[1] partial performance recovery during interrupted operation[2] and permanent cell degradation are assigned to the presence of mobile ionic charge carriers. Their characterization in full devices is therefore of outmost importance to improve this type of solar cell.

In this study, we first discuss the characteristics of formamidinium-based perovskite solar cells with non-stochiometric compositions. It is found that a 1-1.5% excess of formamidinium precursor (FAI) leads to an improved stabilized device performance while further increasing the FAI excess detrimentally affects the fill factor. Through electrical impedance spectroscopy measurements, it is revealed that the increased FAI excess leads to a higher ionic conductivity. In order to further distinguish between the density and mobility of the ions, we simulate IV and impedance data with the simulation software Setfos.[3] The experimental trends with increasing FAI excess can only be reproduced with an increased density of ions in the simulation.[4]

In general, one would like to distinguish directly between ionic mobility and density in a single solar cell. A method that has been introduced decades ago[5] and was applied recently to perovskite solar cells is the transient ion drift measurement.[6] The analytical model describing the capacitance over time is based on several assumptions that are not necessarily fulfilled in a perovskite devices. We use drift-diffusion simulations in Setfos to model the transient ion drift experiment and thereby confirm the limitations of the analytical model. We further show that those limitations can be overcome by combining measurement and simulations, allowing the application of the method to a broader set of devices.

This work was supported by the SOLAR-ERA.NET Cofund 2 786483, project SCALEUP (Swiss Federal Office of Energy: SI/501958-01 and Spanish Ministry of Science: PCI2019-111839-2)

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