Sky-blue Solution-processed TADF and Hyperfluorescent OLEDs via a High-Work-Function PEDOT:PSS:PFI Hole Injection Layer
Solution-processed OLEDs offer a scalable route to large-area devices, but achieving competitive efficiency in multilayer stacks remains a challenge due to difficulties in hole injection as well as solvent orthogonality between layers. A hole injection layer (HIL) based on a blend of PEDOT:PSS and a perfluorinated ionomer (PFI) addresses both challenges simultaneously: surface segregation of PFI during film drying creates a high-work-function interface improving hole injection into high-ionisation potential host materials, while the insolubility of the blend in aromatic solvents prevents intermixing with subsequently deposited layers. Using this HIL with a solution-processed mCPCN:SpiroAC-TRZ emissive layer, sky-blue OLEDs with a peak external quantum efficiency (EQEmax) of 21.7%, an external quantum efficiency (EQE) of 20.2% at 100 cd m-2, a peak luminance of 29,000 cd m-2 and a full width at half maximum (FWHM) emission linewidth of 69 nm are demonstrated. The PFI-based HIL approach is extended to the photochemically stable TADF emitter 5TCzBN (EQEmax 18.4%, FWHM 73 nm) and to sensitized / hyperfluorescent OLEDs incorporating the multi-resonance TADF terminal emitters n-DABNA (EQEmax 22.8%, FWHM 26 nm) and the dendrimer TCzBN-BMes (EQEmax 20.4%, FWHM 29 nm). These results establish the PEDOT:PSS:PFI HIL as a broadly compatible platform for high-performance solution-processed TADF OLEDs.