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

Abstract

AbstractThe 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−2, a current efficiency of 27.5 cd A−1, 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.