Highly Efficient Red-Emitting Hybrid Polymer Light-Emitting Diodes via Forster Resonance Energy Transfer Based on Homogeneous Polymer Blends with the Same Polyfluorene Backbone

Highly efficient inverted-type red-emitting hybrid polymeric light-emitting diodes (HyPLEDs) were successfully demonstrated via Forster resonance energy transfer (FRET) and interfacial engineering of metal oxide with a cationic conjugated polyelectrolyte (CPE). Similarly structured green- and red-emissive polyfluorene copolymers, F8BT and F8TBT, were homogeneously blended as a FRET donor (host) and acceptor (dopant). A cationic polyfluorene-based CPE was also used as an interfacial layer for optimizing the charge injection/transport and improving the contact problem between the hydrophilic ZnO and hydrophobic polymer layer. A long Forster radius (R-0 = 5.32 nm) and high FRET efficiency (similar to 80%) was calculated due to the almost perfect spectral overlap between the emission of F8BT and the absorption of F8TBT. A HyPLED containing 2 wt % F8TBT showed a pure red emission (lambda(max) = 640 nm) with a CIE coordinate of (0.62, 038), a maximum luminance of 26 400 cd/m(2) (at 12.8 V), a luminous efficiency of 7.14 cd/A (at 12.8 V), and a power efficiency of 1.75 lm/W (at 12.8 V). Our FRET based HyPLED realized the one of the highest luminous efficiency values for pure red emitting fluorescent polymeric light emitting diodes reported so far.