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

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‐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.

P‐16.1: Fully Inkjet‐Printed Organic Light‐Emitting Diodes based on a Thermally Activated Delayed Fluorescent Emitter

“…Thermally activated delayed fluorescent (TADF) materials represent a new generation of pure organic materials with theoretically achievable internal quantum efficiencies of 100%, playing a pivotal role in current OLED development. 3 While some reports 1,4 have described the successful fabrication of OLEDs using inkjet printing by vacuum depositing the electrontransporting layer onto the TADF emitting layer, there is a noticeable absence of literature on fully printed OLEDs based on TADF materials. This scarcity can be attributed to the inherent challenges associated with TADF small molecules, which typically exhibit low resistance to solvents, even orthogonal solvents.…”