Toward Highly Efficient Solution‐Processable OLEDs: Inkjet Printing of TADF Emissive Layer
Marco Cinquino, Carmela Tania Prontera, Antonio Maggiore, Alessandra Zizzari, Marco Pugliese, Fabrizio Mariano, Vitantonio Valenzano, Ilaria Elena Palamà, Riccardo Manfredi, Giuseppe Gigli, Vincenzo Maiorano
Abstract
Abstract 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‐9 H ‐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.