Realizing 17.0% external quantum efficiency in red quantum dot light-emitting diodes by pursuing the ideal inkjet-printed film and interface

Since the layer erosion often happens during the solution-processable optoelectronic devices, and thus the efficiency of inkjet-printed quantum dot light emitting diodes (QLEDs) lags behind those of spin-coated counterparts severely. Indeed, the pursuit of high-performance inkjet-printed QLEDs is fundamentally challenging. Herein, a binary QDs ink based on cyclohexylbenzene (CHB) and indane was developed with red CdZnSe/ZnS core/shell structure without using any other additives for inkjet printing. Three common hole transport materials (HTMs), poly (9-vinlycarbazole) (PVK), poly[(9,9'-dioctylfluorenyl-2,7- diyl)-co-(4,4'-(N-(4-sec-butyl))diphenylamine)] (TFB) and poly (N, N′-bis (4-butylphenyl-N, N′-bis (phenyl) benzidine) (Poly-TPD), were invoked as the underlying layer to print QDs emissive layer, and their surface wettability and solvent resistance were systematically investigated. Among them, PVK exhibited excellent surface wettability and solvent resistance, accordingly, the PVK-based printed red QLEDs exhibited the current efficiency of 28.8 cd A−1 and the maximum external quantum efficiency (EQE) over 17.0%, which was comparable to the spin-coated QLEDs (19.8%). These results demonstrate the fabrication of efficient inkjet-printed QLED devices, which will be meaningful for printed QLEDs displays.