Toward Highly Efficient Solution-Processable OLEDs: Inkjet Printing of TADF Emissive Layer

The fabrication of optoelectronic devices using low-cost inkjet printing techniques is a topic of great interest to the scientific and industrial community and represents a step toward the full deployment of solution-processable organic light emitting diodes (OLEDs), particularly for commercial lighting and signaling applications. Herein, the inkjet printing of tBuCzDBA (9,10-bis(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)-2,6-dimethylphenyl)-9,10-diboraanthracene) is reported, a high-performing thermally activated delayed fluorescence (TADF) emitter for OLEDs. Optimizing the surface tension values of the ink formulations and the associated wetting behavior are crucial parameters for achieving a uniform and homogeneous printed thin film. In particular, it is observed that using a proper mixture of solvents with different surface tensions, it is possible to generate Marangoni flows inside the drop, which triggers a very fast drying process, ensuring optimized morphological and optical properties in the inkjet printed tBuCzDBA-based film. OLEDs exploiting this film as an emissive layer are then fabricated, achieving a maximum luminance of 32 000 cd m, a current efficiency of 27.5 cd A, and an external quantum efficiencyof 10%. To the best of the knowledge, this is the highest efficiency reported to date for self-hosted TADF inkjet-printed OLEDs.