Polaron transport of amorphous semiconductors with embedded crystallites

ABSTRACT

Near-room-temperature (narrow-band) polaron transport of an amorphous semiconductor with embedded annealing-induced semiconducting crystallites is treated within an effective-medium approach. Carrier mobilities in the crystallites are assumed much larger than those of the amorphous phase. Nonetheless, crystallites act as macroscopic traps when their carriers’ energies lie below those in the amorphous phase. Then the mixture’s dc conductivity falls below that of the amorphous phase at low enough carrier concentrations. However, with increasing carrier concentration the shifting chemical potential diminishes this trapping effect, enabling crystallites’ larger mobilities to drive the mixtures’ electrical conductivity above that of the amorphous phase. Meanwhile the Seebeck coefficient remains insensitive to the annealing-induced introduction and growth of embedded crystallites. These features are qualitatively similar to those reported for an amorphous organic polymer FET with annealing-induced embedded crystallites.

KEYWORDS:

• Amorphous semiconductors
• electrical conductivity
• polarons
• polycrystalline
• Seebeck coefficient
• mixtures

Acknowledgements

The author gratefully acknowledges that this study was motivated by extensive interactions with Henning Sirringhaus and his associates, primarily Martin Statz and Riccardo Di Pietro, who shared their data on the effects of annealing on the field-effect mobility and Seebeck coefficient of films of the partially crystalised polymer P(NDI20D-T2).

Disclosure statement

No potential conflict of interest was reported by the author.

ORCID

David Emin http://orcid.org/0000-0003-2125-669X