Conjugated Polyelectrolyte Hybridized ZnO Nanoparticles as a Cathode Interfacial Layer for Efficient Polymer Light-Emitting Diodes

Alkoxy side-chain tethered polyfluorene conjugated polyelectrolyte (CPE), poly[(9,9-bis((8-(3-methyl-1-imidazolium)octyl)-2,7-fluorene)-alt-(9,9-bis(2-(2-methoxyethoxy)ethyl)-fluorene)] dibromide (F8imFO(4)), is utilized to obtain CPE-hybridized ZnO nanoparticles (NPs) (CPE:ZnO hybrid NPs). The surface defects of ZnO NPs are passivated through coordination interactions with the oxygen atoms of alkoxy side-chains and the bromide anions of ionic pendent groups from F8imFO(4) to the oxygen vacancies of ZnO NPs, and thereby the fluorescence quenching at the interface of yellow-emitting poly(p-phenylene vinylene)/CPE:ZnO hybrid NPs is significantly reduced at the CPE concentration of 4.5 wt%. Yellow-emitting polymer light-emitting diodes (PLEDs) with CPE(4.5 wt%):ZnO hybrid NPs as a cathode interfacial layer show the highest device efficiencies of 11.7 cd A(-1) at 5.2 V and 8.6 lm W-1 at 3.8 V compared to the ZnO NP only (4.8 cd A(-1) at 7 V and 2.2 lm W-1 at 6.6 V) or CPE only (7.3 cd A(-1) at 5.2 V and 4.9 lm W-1 at 4.2 V) devices. The results suggest here that the CPE:ZnO hybrid NPs has a great potential to improve the device performance of organic electronics.