Investigation on slot-die coating of hybrid material structure for OLED lightings

With an attempt to fabricate large-area OLED lighting panels, we investigate slot-die coating of a small molecule (SM) hole transport layer (HTL). It is observed that SM HTL films formed by spin coating exhibit pinhole-like surface, whereas the films by slot-die coating show micro-sized hillocks due to agglomeration. As the plate temperature of the slot coater is increased, smaller hillocks appear more densely. To tackle it, a small amount of a polymer HTL is added into the SM HTL (Hybrid HTL). By the aid of entangled polymer chains, small molecules are prohibited from migrating and thus agglomerations disappear. The peak-to-peak roughness of the slot-coated hybrid HTL films is measured to be about 11.5nm, which is slightly higher than that (~7nm) of the polymer HTL film, but much lower than that (~1071nm) of the SM HTL film. Similar results are also observed in spin-coated films. It is also addressed that OLED with the hybrid HTL shows higher luminous efficacy, compared to OLED with the SM HTL or the polymer HTL. We have further demonstrated that the dissolution problem occurring between two stacked layers with different solvents during slot-die coating can be suppressed to a great extent using such a combination of materials in hybrid structure. •We investigate slot-die coating of small molecule HTLs for large-area OLED lightings.•The surface morphology is much enhanced by the addition of entangled polymer chains.•OLED with slot-coated hybrid HTL shows higher luminous efficacy.•Such a hybrid material system also suppresses the dissolution phenomenon to a great extent.