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Band gap engineering in blended organic semiconductor films based on dielectric interactions

Abstract

Blending organic molecules to tune their energy levels is currently being investigated as an approach to engineer the bulk and interfacial optoelectronic properties of organic semiconductors. It has been proven that the ionization energy and electron affinity can be equally shifted in the same direction by electrostatic effects controlled by blending similar halogenated derivatives with different energetics. Here we show that the energy gap of organic semiconductors can also be tuned by blending. We use oligothiophenes with different numbers of thiophene rings as an example and investigate their structure and electronic properties. Photoelectron spectroscopy and inverse photoelectron spectroscopy show tunability of the single-particle gap, with the optical gaps showing similar, but smaller, effects. Theoretical analysis shows that this tuning is mainly caused by a change in the dielectric constant with blend ratio. Further studies will explore the practical impact of this energy-level engineering strategy for optoelectronic devices.

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Fig. 1: Overview over the molecules used.
Fig. 2: Two-dimensional GIWAXS plots of neat films and blends.
Fig. 3: Comparison of the 3T dimer and 6T monomer.
Fig. 4: Results of the photoelectron spectroscopy measurements.
Fig. 5: Comparison of the simulated and experimental changes in the IE and the single-particle gap.

Data availability

The data that support the findings of this study are available from https://archive.materialscloud.org/deposit/records/832.

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Acknowledgements

K.O., J.K. and K.L acknowledge financial support by the German Research Foundation (DFG) (project LE 747/60-1) and the Graduate Academy of TU Dresden and thank Heliatek GmbH (Dresden) for providing additional materials. S.H. would like to thank Studentenwerk Dresden for funding through the Saxony State Scholarship programme. Additionally, the authors would like to acknowledge support by the German Excellence Initiative via the Cluster of Excellence EXC 1056 ‘Center for Advancing Electronics Dresden’ (cfaed). J.B. acknowledges the DFG project VA 1035/5-1 (Photogen) and the Sächsische Aufbaubank through project number 100325708 (InfraKart). The GIWAXS experiments were performed at the BL11 NCD-SWEET beamline at ALBA Synchrotron with the collaboration of ALBA staff. The authors would like to thank E. Solano for help with setting up the GIWAXS measurements. We acknowledge Elettra Sincrotrone Trieste for providing access to its synchrotron radiation facilities and we thank L. Barba for assistance in using beamline XRD-1. The research leading to this result has been supported by the project CALIPSOplus under Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Moreover, F.O. would like to thank the DFG for funding through projects OR 349/1 and OR 349/3, the Cluster of Excellence e-conversion (grant number EXC2089) and the Zentrum für Informationsdienste und Hochleistungsrechnen of TU Dresden (ZIH) for grants of computing time.

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K.O., M.H., K.T., B.W., J.B., J.K. and F.T. carried out the experiments and data analysis. S.H., S.S. and F.O. performed the calculations. A.V. and P.B. synthesized the 6T molecules. K.O., K.L., S.H. and F.O. wrote the paper. All authors contributed to the discussion and commented on the manuscript.

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Correspondence to Frank Ortmann or Karl Leo.

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Supplementary Figs. 1–9, Table 1, Sections 1–5.

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Ortstein, K., Hutsch, S., Hambsch, M. et al. Band gap engineering in blended organic semiconductor films based on dielectric interactions. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-01025-z

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