Enhancing hole carrier injection via low electrochemical doping on circularly polarized polymer light-emitting diodes

Circularly polarized electroluminescence (CP-EL) from a blend system of chiral small-molecule additives and device optimised achiral pi-conjugated polymers (pi-CPs) is of great interest for next-generation display technologies. However, CP polymer light-emitting diodes can suffer from unbalanced charge transport and unfavorable energetics between chiral additives and achiral polymers, which can limit the efficiency of charge injection and device performance. Herein, we demonstrate the use of a small amount of chemcially modified electrochemical doping agent (EDA, 1.5 wt%) to control such limitations. The EDA with a long cationic alkyl chain enables strong hydrophobicity and stable electrochemical doping of achiral pi-CP F8BT in F8BT:aza[6]H blends, which allows for better charge injection and balance. This leads to improved device performance while maintaining highly dissymmetric electroluminescence (g(EL) similar to 0.50@580 nm) and an inverted dissymmetry factor (g(EL) = -0.65@525 nm). These findings indicate that EDAs may provide a simple approach to improve the performance of CP optoelectronic devices.