Self‐Dopant Formation in Poly(9,9‐di‐n‐octylfluorene) Via a Dipping Method for Efficient and Stable Pure‐Blue Electroluminescence

Dipping pristine poly(9,9-di-n-octylfluorene) film into a mixed solvent/ nonsolvent THF/MeOH transforms the conformation of minor amorphous-phase chains to β-phase conformers (see figure) with a controllable content. The β phase acts as a dopant and causes electron trapping and promoted hole mobility. It allows efficient energy transfer and charge trapping and thus achieves pure-blue electroluminescence and enhanced device performance.