Automated determination of ionization energy and electron affinity from UPS and LEIPS spectra based on piecewise polynomial fitting

Precise determination of ionization energy (IE) and electron affinity (EA) is essential for elucidating the electronic structure of semiconductors. In the solid state, these quantities are most accurately obtained from the spectral onsets of ultraviolet photoelectron spectroscopy (UPS) and low-energy inverse photoelectron spectroscopy (LEIPS), respectively. Conventional onset determination relies on manual fitting, which is time-consuming and requires experience. For future automated measurements, automated data analysis will be indispensable. Here, we propose an automated analysis approach that combines piecewise polynomial fitting with tangent intersection to extract IE and EA from UPS and LEIPS spectra. Applied to various organic semiconductors and polymer samples, the automated results exhibit excellent agreement with manual analysis, achieving accuracies of ±0.002 eV for UPS and ±0.02 eV for LEIPS—well below the commonly assumed uncertainties and instrumental resolutions of these techniques. The method demonstrates robust performance even for spectra with low signal-to-noise ratios or unclear onset, with no outliers exceeding 0.1 eV. This framework offers a reliable solution for automated spectral analysis, paving the way for large-scale database development and data-driven materials discovery. • Automated method extracts IE and EA from UPS and LEIPS spectra accurately. • Piecewise polynomial fitting with tangent intersection ensures robust onset detection. • Achieves ±0.002 eV for UPS and ±0.02 eV for LEIPS, closely matching manual analysis. • Works reliably for spectra with low S/N ratios or gradual onsets without outliers. • Enables integration with automated systems for large-scale materials informatics.