Dresden 2026 – scientific programme

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O: Fachverband Oberflächenphysik

O 82: Focus Session: Unoccupied States by Inverse Photoemission III

O 82.1: Invited Talk

Thursday, March 12, 2026, 10:30–11:00, WILL/A317

Low-energy inverse photoelectron spectroscopy (LEIPS): probing unoccupied states and conduction band structure in functional materials — •Hiroyuki Yoshida — Chiba University, Chiba, Japan

We developed low-energy inverse photoelectron spectroscopy (LEIPS) in 2012 [1] to enable damage-free probing of functional materials such as organic semiconductors, polymers and hybrid perovskites. By reducing the incident electron energy below the damage threshold (about 5 eV), LEIPS allows damage-free measurements while simplifying operation and improving energy resolution. By incorporating an electron energy analyzer [2], we achieved an energy resolution of 98 meV. LEIPS enables determination of electron affinity with an uncertainty of 0.1 eV. These precise values provide access to key parameters including band gaps, exciton binding energies, polarization energies, and electron injection barriers. The technique has been commercialized, and more than 100 systems are now in operation worldwide. We further developed angle-resolved LEIPS (AR-LEIPS) [3], enabling for the first time direct observation of conduction band structure in organic semiconductors [4]. The measured band structures yield insight into electron-phonon coupling and polaron formation relevant to carrier transport. [1] Chem. Phys. Lett. 539-540, 180 (2012). [2] Rev. Sci. Instrum. 94, 043908 (2023). [3] Rev. Sci. Instrum. 94, 063903 (2023). [4] Nat. Mater. 21, 910 (2022).

Keywords: Low-energy inverse photoelectron spectroscopy; Unoccupied electronic states; Organic semiconductors; Electron affinity; Conduction band structure