Proceedings of MATSUS Spring 2025 Conference (MATSUSSpring25)
DOI: https://doi.org/10.29363/nanoge.matsusspring.2025.418
Publication date: 16th December 2024
Electrochemical impedance spectroscopy measurements of perovskite solar cells (PSCs) show characteristic features at low frequencies, such as a large illumination-dependent capacitance [1,2]. While this effect is well known, the debate on its origin persists [3,4]. An illumination-dependent increase in the conductivity of ionic charge carriers was suggested early on [2]. However, experiments to elucidate the presence of such a photo-conductive effect require special devices or measurement techniques and neglect possible influences of the enhanced electronic charge concentrations. Thus, only a few studies investigated this effect in detail.
Using drift-diffusion simulations and two novel techniques to analyze the simulation results, we show how the illumination-dependent part of the capacitance originates from electronic currents that are amplified due to the screening of the alternating electric field by the ions [5]. This is inherently caused by the mixed electronic-ionic interaction. Counter-intuitively, an illumination-dependent ion conductivity even reduces the magnitude of the capacitance increase.
As the presence and magnitude of a low-frequency capacitance increase by itself are unsuited to assess the presence of illumination-dependent ion conductivity, we propose a novel characterization technique based solely on capacitance measurements at short-circuit on fully integrated devices. The frequency shift of the onset in capacitance is extracted at varying illumination intensity. This quantity shows a distinct qualitative difference depending on whether the ion conductivity depends on illumination or is constant. As these measurements can be performed on unaltered, fully integrated devices and with standard equipment, the method is well suited for widespread investigation of a photo-conductive effect in different materials and devices or in response to degradation.
The method is applied to a range of perovskite solar cells with different active layer materials. Remarkably, all measured samples show a clear signature of photoenhanced ion conductivity, posing fundamental questions on the underlying nature of the photosensitive mechanism.
The authors thank Solaronix SA and Prof. Chenyi Yi from Tsinghua University for fabricating and providing PSCs. This work has been partially funded through the Swiss National Science Foundation (SNF) project ”RADICALS” (Project No. 216647), the European Union’s Horizon 2020 research and innovation programme (Marie Skłodowska-Curie grant No. 945363, ERC StGrt No. 851676), as well as the Innosuisse project ”AIPV” (Grant No. 58054.1 IP-EE).
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