Advanced characterization of charge carrier dynamics in perovskite solar cells using impedance spectroscopy

Date

2025-3

Author

Şahiner, Mehmet Cem

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The emerging field of organic–inorganic hybrid perovskite materials presents a promising alternative for low-cost, solution-processable optoelectronic devices. While the efficiency of perovskite photovoltaic cells has advanced rapidly, a substantial gap remains between the understanding of device physics and the practical competence in fabrication techniques. To help bridge this gap, this study focuses on elucidating the fundamental charge carrier dynamics in perovskite solar cells using impedance spectroscopy—an informative characterization technique applicable across a wide range of operating conditions. Carrier recombination and transport dynamics were investigated using impedance spectroscopy, complemented by drift-diffusion simulations, electroluminescence measurements, and intensity-modulated small perturbation methods. Novel approaches to both measurement and simulation techniques were developed and validated across various cell architectures and configurations. A detailed analysis of perovskite bulk composition and surface passivation strategies was conducted. By decoupling the effects of voltage bias and light intensity on impedance response, the stoichiometric balance between lead iodide and formamidinium iodide was optimized. Lead iodide-rich compositions reduced recombination loss, while increased formamidinium content enhanced transport properties. Further improvements in charge carrier mobility were achieved by incorporating cesium and bromide ions. Effective surface passivation of nickel oxide layers via self-assembled monolayers demonstrated cells exhibiting over 20% power conversion efficiency with 0.1 V photovoltage increase, attributed to the mitigation of Fermi-level pinning. Additionally, the insertion of a two-dimensional perovskite nanolayer between the bulk perovskite and spiro-OMeTAD hole transport layer was shown to both passivate the interface and electronically shield the cell from metal contact deterioration.

Subject Keywords

Perovskite solar cells, Impedance spectroscopy, Drift-diffusion simulations, Electroluminescence efficiency, Recombination dynamics

URI

https://hdl.handle.net/11511/114088

Collections

Graduate School of Natural and Applied Sciences, Thesis