Issue 1, 2020

Spectator cation size effect on the work function and stability of self-compensated hole-doped polymers

Abstract

The ‘free’ ions needed to balance the ‘fixed’, covalently bonded ions in a conventional polyelectrolyte are often thought to play little role beyond charge balancing, processability and morphology control. In self-compensated, hole-doped polymers, free cations, together with mobile holes on the polymer backbone, balance the covalently tethered counter-anions. We show here that these ‘spectator’ cations not only influence the ionization energy (and work function) of the polymer, but also, perhaps surprisingly, determine the stability of the ultrahigh-workfunction state. We attribute these two effects to the dependence on the spectator cation size of surface ionic layering, and coulombic stabilization of the anion sites, respectively. The smaller cations provide larger coulombic stabilization of the anionic site, raising the energetic barrier for hole transfer to the anion or its hydration water, thereby blocking de-doping of the polymer backbone. We demonstrate these effects in an important model of a high-ionization-energy triarylamine–fluorene copolymer TFB with trifluoromethanesulfonylimidosulfonyl as a tethered counter-anion, and a family of spherical monovalent cations as spectators (Li+, Na+, Cs+, NMe4+ and NEt4+). Using Li+ as a spectator cation, we further demonstrate ultrahigh-workfunction hole injection layers for TFB semiconductor with markedly enhanced stability to ambient processing and baking. This work leads to a new design rule for stable, self-compensated, hole-doped polymer systems with ultrahigh work function.

Graphical abstract: Spectator cation size effect on the work function and stability of self-compensated hole-doped polymers

Supplementary files

Article information

Article type
Paper
Submitted
18 Jul 2019
Accepted
14 Nov 2019
First published
15 Nov 2019

J. Mater. Chem. C, 2020,8, 124-131

Spectator cation size effect on the work function and stability of self-compensated hole-doped polymers

M. C. Ang, Q. Koh, C. G. Tang, Q. Seah, Y. Wang, M. Callsen, Y. Feng, R. Png and L. Chua, J. Mater. Chem. C, 2020, 8, 124 DOI: 10.1039/C9TC03884A

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements