WITHDRAWN: Environmental stability enhancement through light mediated cross-linking of eco-friendly quantum dot for printed light emitting diode

Abstract Printed quantum dot (QD) light emitting diodes (QLEDs) have received much interest in the last decade owing to the demand for low-cost large-area displays for consumer electronics. Previous studies demonstrated printed QLEDs with CdSe core/shell quantum dots using a co-solvent system or polymer additive. However, limited solvent choice and environmental restrictions such as temperature, O2/H2O level, and viscosity make it difficult to control the thickness and surface roughness of the printed layer, resulting in low maximum luminescence and low external quantum efficiency (EQE) compared to that achievable by spin coating. Moreover, eco-friendly QLEDs are significantly difficult to fabricate under ambient conditions and are prone to electrochemical and thermal degradation, unlike stable ionic-bonded Cd-based QDs. Herein, we design a universal ink for the ambient inkjet printing of QLED devices via photoinitiator (PI) mediated cross-linkage. The PI modulates the ink properties to make it compatible with inkjet printing onto the desired surface. Once the material is deposited on the surface, its film polymerizes in situ through radical formation induced by ultraviolet (UV) exposure. Cross-linking reactions between ligands in the nanomaterials (e.g., oleic acid) reduce the distances between them, leading to flattening of the surface and enhancement of environmental stability. As a result, printed QLEDs could be fabricated under ambient conditions. InP-based QD and CdSe/ZnS QD demonstrated maximum luminescence values of 3600 cd/m2 at 10 V and 2.4 × 104 cd/m2 at 12 V on ITO/glass, respectively. Finally, bird-shaped red/green/blue mixed electroluminescence (EL) devices were produced on glass and polyethylene naphthalate (PEN) substrate.