Wet-Deposited TADF-Based OLED Active Layers: New Approaches towards Further Optimization

Abstract

The effects of the solvent used for the active layer materials of an OLED based on TADF emitters play a fundamental role in solution-deposited devices. This work focuses on the effects on the performance of different solvents employed to fabricate a very simple two-organic-layer OLED based on a green TADF emitter, under the concept of host: guest matrix. From the different results of the main figures of merit, it was possible to conclude that the OLED that used toluene as a solvent for the active layer reached a maximum EQE of 14%, almost the maximum already obtained for this emitter in more complex device structures. With the analysis of the charge-transport processes, it was possible to establish an explanatory model for the obtained results. Through impedance spectroscopy, additional characterization of the nature of charge-transport processes was carried out. With these results, it was possible to correlate the relaxation times, with the electrical properties of the active layer, and make inferences about the interaction between the electrical charges and the defect levels, opening new possibilities for further development in printed OLEDs.