Dresden 2026 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 83: Organic molecules on inorganic substrates: electronic, optical and other properties III

O 83.9: Vortrag

Donnerstag, 12. März 2026, 17:00–17:15, HSZ/0201

Exciton Dynamics and Charge Transfer at Prototype Organic/Organic Interfaces Studied with LEEM and 2P-PEEM — Franz Niklas Knoop, •Klaus Stallberg, and Winfried Daum — Institute of Energy Research and Physical Technologies, TU Clausthal, Germany

Organic semiconductor (OSC) films deposited on weakly interacting substrates, such as natively oxidized silicon, often suffer from poor structural order. Using low-energy electron microscopy (LEEM), we show that para-sexiphenyl (p-6P) molecules on SiO₂ serve as a wetting layer, promoting the growth of microcrystalline phthalocyanine (Pc) thin films, which renders Pc/p-6P/SiO₂ a structurally well-defined model for an organic heterojunction. Using two-photon photoemission (2PPE), we study the exciton dynamics in both CuPc and F₁₆CuPc films on p-6P/SiO₂. For F₁₆CuPc/SiO₂, i.e., in absence of p-6P, the S₁ exciton is observed with a lifetime of 50 ps, indicating negligible influence of the substrate on the exciton dynamics. In contrast, for F₁₆CuPc/p-6P/SiO₂, the S₁ exciton is quenched. Moreover, laser-induced changes in electron reflectivity reveal a surface potential shift for F₁₆CuPc/p-6P/SiO₂, which points to the formation of surface dipoles upon optical excitation of F₁₆CuPc. Accordingly, we attribute the S₁ exciton quenching to formation of charge transfer (CT) excitons, which is compatible with the type II energy level alignment at the F₁₆CuPc / p-6P interface. In contrast, at the CuPc/p-6P type I heterojunction no charge transfer takes place. Accordingly, neither exciton quenching nor significant surface potential shifts are observed.

Keywords: LEEM; PEEM; photoemission; organic semiconductor