Band Structure Engineering in Highly Crystalline Organic Semiconductors

TL;DR

This paper demonstrates that band structure engineering in highly crystalline organic semiconductors can be achieved through molecular blending, with delocalization playing a key role, supported by spectroscopic and theoretical analysis.

Contribution

It shows for the first time that electronic delocalization in highly ordered organic crystals can be used to engineer their band structure, similar to inorganic semiconductors.

Findings

Delocalization significantly influences energy structure in organic crystals.

Spectroscopic methods confirm band structure modifications.

Theoretical simulations support experimental observations.

Abstract

Blending of semiconductors for controlling the energy levels (band structure engineering) is an important technique, in particular, for optoelectronic applications. The underlying physics is the delocalized Bloch states, which average over the potential landscape of the blend. For organic semiconductors, it has been shown that two quite different effects, the dielectric constant and electrostatic interaction between molecules, can be used to tune the energy gap and ionization energy of disordered and weakly crystalline organic semiconductor blends. It is so far not known whether the electronic delocalization in organic crystals with large bandwidths can contribute to the energy structure engineering of the blend in a way similar to that in inorganic semiconductors. Here, we investigate the growth of highly ordered organic thin-film blends with a similar chemical structure and show the effect of band structure engineering by spectroscopic methods. We rationalize the experimental results with comprehensive theoretical simulations, showing that the delocalization is a significant effect. Our work paves the way for engineering the band structure of highly ordered organic semiconductor thin films that can be tailored for the desired optoelectronic device application.