Poly(9,9-dialkylfluorene-co-triphenylamine)s – A family of photo-curable hole-transport polymers for polymer light-emitting diodes applications

• The photo-curable HTLs are obtained by the formation of the benzylic cation and via Friedel Crafts reaction.
• Under UV exposure, 1, 2 and DIAS as a photocrosslinking agent for PFTs could be transferred to HTL.
• The optimization device has a turn-on voltage of 9.4 V (1 cd/m2), a Lmax of 7630 cd/m2, and a nc,max of 15.8 cd/A.
• From lifetime experiment, the device is 1.8 times more stable than the STD device.

Hole-transporting photocurable blends of (4-(AcOCH2)C6H4)3N (1) or ((4-(AcOCH2)C6H4)2NC6H4)2 (2), poly(fluorene-co-triphenylamine)s (PFTs) and diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS, a photoacid generator (PAG)) have been successfully formulated. Under UV irradiation (λ > 200 nm), PAG decomposes to release protons that catalyze the heterolytic decomposition of 1 and 2 to give benzylic cation intermediates. Friedel–Crafts type electrophilic aromatic substitution would then occur at the triphenylamine (TPA) units of PFT, leading to a photo-curing phenomenon. The curing efficiency is therefore highly dependent on the content of TPA in the PFT. This approach can be implemented to PLED applications. Under the optimized conditions, the polymeric light-emitting device of ITO/photo-cross-linkable HTL/PVK-Ir(ppy)3-t-PBD/Mg–Ag, with a turn-on voltage of 9.4 V (1 cd/m2), a maximum brightness of 7630 cd/m2, and a current efficiency of 15.8 cd/A was achieved. The lifetime of the device has also been improved by 1.8 times when compared with that of the STD device.

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