Demonstration of Charge Mobility Mechanism in Organic Single Crystal

Charge-conducting organic materials could be used in many inspiring applications, including low-cost solar cells and flexible electronic devices.

This is a representation of carrier mobility in hard inorganic materials (upper figure, band transport) and flexible organic solids (lower figure, flexibility induced transport mechanism). (Image credit: Kazuyuki Sakamoto)

However, until now, only organic light-emitting diodes (OLEDs) have made a productive impact due to research gaps in organic semiconductors that have restricted enhancements toward charge carrier mobility.

An international team of researchers, including scientists at Osaka University, has shown the charge mobility mechanism in an organic single crystal. The study outcomes have been reported in Scientific Reports.

Scientists attempted to enhance the charge carrier mobility in organic crystals by essentially focusing on the understanding of the effect of the organic single crystals’ electronic structure on the charge mobility. The analysis of highly ordered single crystals rather than samples with various defects and disorders produced the most precise view of the movement of charge carriers in the organic material.

The scientists analyzed a single crystal of rubrene, which is one of the most significant conducting organic materials due to its high charge mobility. Although rubrene is well known, its electronic structure is not yet understood exactly. They discovered that theory-based conclusions deduced in earlier studies were imprecise due to molecular vibrations at ambient temperature as a result of material flexibility.

We have demonstrated a new mechanism that is not observed for traditional inorganic semiconductor materials. Inorganic semiconductors such as silicon, which are widely used in electronics, are generally hard, inflexible materials; therefore, certain assumptions made for these materials do not translate to organic conducting materials that are more flexible.

Kazuyuki Sakamoto, Study Corresponding Author, Osaka University

They successfully prepared an ultra-high-quality single rubrene crystal sample, which enabled them to conduct experiments to obtain a conclusive comparison with earlier data. The experiments emphasized the limitations of earlier assumptions and showed the impact of other factors like molecular vibrations and electron diffraction.

By reliably demonstrating the room temperature behavior of an organic conducting material and reframing the thinking behind previous conclusions that have been drawn, we have provided a much clearer basis for research going forward.

Kazuyuki Sakamoto, Study Corresponding Author, Osaka University

He added, “We hope that this insight will accelerate the development of flexible conducting devices with a wide range of exciting functions.”


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