Regensburg 2025 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 27: Molecular Electronics and Excited State Properties II

CPP 27.4: Talk

Wednesday, March 19, 2025, 12:15–12:30, H38

Enhancing excitonic properties in organic semiconductors by aqueous ions — •Filip Podjaski — Department of Chemistry and Centre for Processable Electronics, Imperial College London, UK

While organics semiconductors (OSC) promise tailorable structure-function relationships for enhanced solar energy conversion abilities, advancement is often hindered by limiting knowledge of interwoven photo-physical processes and properties that lead to recombination losses on ultrafast time scales.[1] Herein, I discuss possibilities to measure and modify functionalized OSC' exciton behaviour, to address their recombination. For photocatalysis, interactions with aqueous ions, which are also relevant for enabling sea water use, are typically disregarded. Our time-resolved optical spectroscopy study on suspended polymer nanoparticles in presence of different salts shows how they can improve stabilization of excitons. We further introduce Terahertz permittivity measurements as convenient tool to probe the complex permittivity / dielectric properties of OSCs on ps-time scales. The permittivity defines exciton binding energy and is hence relevant for charge carrier photogeneration and transport. But its highly frequency dependent values are commonly extracted orders magnitude off the ps-regime. Our study focussing on carbon nitrides now reveals dielectric screening and transport properties at the early time scales of solar energy conversion process chains, and illustrates environmental enhancements enabled by ions.[2]

References: [1] Nat. Rev. Mater. 6, 168-190 (2021). [2] R. Jahangir, F. Podjaski et al., submitted, arxiv.org/abs/2411.06226

Keywords: Excitonic properties; Organic semiconductors; Time-resolved optical spectroscopy; Solar energy; Terahertz spectroscopy