Hole-phonon coupling effect on the band dispersion of organic molecular semiconductors

F Bussolotti,K Tanaka,K Yonezawa,J Yang,K Sato,S Kera,T Yamaguchi,N Ueno,M Matsunami,H Ishii,Y Nakayama

doi:10.1038/s41467-017-00241-z

Abstract

The dynamic interaction between the traveling charges and the molecular vibrations is critical for the charge transport in organic semiconductors. However, a direct evidence of the expected impact of the charge-phonon coupling on the band dispersion of organic semiconductors is yet to be provided. Here, we report on the electronic properties of rubrene single crystal as investigated by angle resolved ultraviolet photoelectron spectroscopy. A gap opening and kink-like features in the rubrene electronic band dispersion are observed. In particular, the latter results in a large enhancement of the hole effective mass (> 1.4), well above the limit of the theoretical estimations. The results are consistent with the expected modifications of the band structures in organic semiconductors as introduced by hole-phonon coupling effects and represent an important experimental step toward the understanding of the charge localization phenomena in organic materials.

Highlights

The dynamic interaction between the traveling charges and the molecular vibrations is critical for the charge transport in organic semiconductors
Local change in the band curvature was predicted to appear in the band dispersion of organic semiconductors, originating from the charge coupling with molecular vibrations[11]
We report on the angle resolved ultraviolet photoemission spectroscopy (ARUPS) investigation of the band dispersion of rubrene single crystal

Summary

Introduction

The dynamic interaction between the traveling charges and the molecular vibrations is critical for the charge transport in organic semiconductors. The hole/electron coupling with intermolecular vibrations was discussed as a possible origin of charge localization, as related to the continuous modulation of the spatial overlap between molecular wavefunctions[7,8,9,10] In this context, experimental studies on the impact of the charge-phonon coupling on the electronic properties of the organic molecular semiconductors may provide critical information (i.e., coupling strength, phonon energies, and so on) for refining the details of the various transport models and/or testing the validity of the corresponding predictions. The results are consistent with the expected modifications of the band structures in organic semiconductor as introduced by hole-phonon coupling effects, as predicted by theoretical calculations on organic models system[11] This result directly confirms the leading role of molecular vibrations in affecting the charge localization in organic single crystals, which is critical for charge mobility[6,7,8, 12,13,14,15]

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Results

Conclusion