No abstract

Photo-patterning and crosslinking of polymer semiconductors, charge injection and/or transport layers are essential to improve the performance and/or functionality of organic semiconductor devices.

It is widely thought that the water-oxidation reaction limits the maximum work function to about 5.25 eV for hole-doped semiconductors exposed to the ambient, constrained by the oxidation potential of air-saturated water. Here, we show that polymer organic semiconductors, when hole-doped, can show work functions up to 5.9 eV, and yet remain stable in the ambient. We further show that de-doping of the polymer is not determined by the oxidation of bulk water, as previously thought, due to its general absence, but by the counter-balancing anion and its ubiquitously hydrated complexes. The effective donor levels of these species, representing the edge of the ‘chemical’ density of states, can be depressed to about 6.0 eV below vacuum level. This can be achieved by raising the oxidation potential for hydronium generation, using large super-acid anions that are themselves also stable against oxidation. In this way, we demonstrate that poly(fluorene-alt-triarylamine) derivatives with tethered perfluoroalkyl-sulfonylimidosulfonyl anions can provide ambient solution-processability directly in the ultrahigh-workfunction hole-doped state to give films with good thermal stability. These results lay the path for design of soft materials for battery, bio-electronic and thermoelectric applications.

Self-compensated hole- and electron-doped polyelectrolytes can afford 0.1 eV tuning steps in work function of charge injection/collection layers through the tethered anions. These material systems are further immune to ‘dopant’ migration.

Spectator cations not only influence the ionization energy (and work function) of polyelectrolyte, but also, surprisingly determine the stability of the ultrahigh workfunction state.