Extracting local carrier dynamics from KPFM surface potential maps Maryam Pourmahdavi [1,2] , Mauricio Schieda [1] , Ragle Raudsepp [1] , Steffen Fengler [1] , Jiri Kollmann [1] , Yvonne Pieper [1] , Thomas Dittrich [3] , Thomas Klassen [2,4] , Francesca M. Toma [1,2,5] [1] Institute of Functional Materials for Sustainability, Helmholtz-Zentrum Hereon, Teltow, Germany, [2] Faculty of Mechanical and Civil Engineering, Helmut Schmidt University, Hamburg, Germany, [3] Nanoscale Solid-Liquid Interfaces, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany, [4] Institute of Hydrogen Technology, Helmholtz-Zentrum Hereon, Geesthacht, Germany, [5] Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA Photoelectrochemical cells are sunlight-driven energy conversion electrochemical devices, which could provide a sustainable and energy efficient route to the generation of valuable chemicals, for instance by the reduction of carbon dioxide (CO 2 ), a potent greenhouse gas. The performance and stability of these devices is highly influenced by the microenvironments at the photoelectrode-electrolyte interface, in particular the local charge carrier distribution and dynamics at the nanoscale. However, few characterization methods are available to expose the intricacies of carrier generation and transport in microscopic detail. Here we implement a methodology for analysis Kelvin Probe Force Microscopy (KPFM), that can be used to track the dynamics of photogenerated carriers on the surface of photoelectrodes with nanometer resolution. We apply the method to a model system: thin films of TiO 2 , deposited by atomic layer deposition (ALD), a material commonly used for protection of photoelectrode surfaces from corrosion. When these films are synthesized with partial crystallinity, their morphology is characterized by crystalline inclusions within an amorphous matrix, resulting in a range of few-hundred nanometer sized domains with significantly different carrier dynamics on the surface of the sample. The local photovoltage on electrode surfaces with such complex compositions can be evidenced using KPFM, by subtracting potential maps under illumination and in dark conditions. We demonstrate a method to obtain photovoltage transients , by algorithmically identifying regions of interest (ROI) based on the photovoltage maps, and tracking the potential evolution for every pixel within the ROIs, across a series of consecutive KPFM images under varying illumination conditions. This allows the extraction of time constants for local carrier dynamic processes, and the discrimination between slow and fast carrier relaxation processes within the nanometer-sized crystalline and amorphous domains. This methodology is a powerful tool that can help understand the microscopic origins of photoelectrode performance limitations, showing pathways for the optimization of light-driven materials and devices. References 1. Pourmahdavi, M. et al. Correlating Local Morphology and Charge Dynamics via Kelvin Probe Force Microscopy to Explain Photoelectrode Performance. PRX Energy 4 , 023010 (2025).
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© The Author(s), 2025
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