Effect of Purification Solvent on Polymer Impurities and Device Performance

Poly(arylamine)s were synthesized by polycondensation of 4-n-octylaniline with 4,4′-dibromobiphenyl using the Buchwald–Hartwig aryl amination. Both the NH and the Br end groups were properly modified upon addition of an end-capping reagent in an appropriate ratio. The synthesized polymers contained many impurities, such as Pd, Br, and Cl, which decrease organic light-emitting diode performance. An investigation to reduce the impurities in the polymer showed that the purification solvent plays the key role in reducing the concentration of impurities in the polymer; purification with a nonchlorinated solvent, anisole, provided a highly pure poly(arylamine) even with a simple purification procedure. Moreover, the highly purified polymer material improved carrier mobility in hole-only devices.