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A novel device structure for thermally activated delayed fluorescence (TADF) top emission organic light-emitting diodes (TEOLEDs) that improves the viewing angle characteristics and reduces the efficiency roll-off is presented. Furthermore, we describe the design and fabrication of a cavity-suppressing electrode (CSE), Ag (12 nm)/WO3 (65 nm)/Ag (12 nm) that can be used as a transparent cathode. While the TADF-TEOLED fabricated using the CSE exhibits higher external quantum efficiency (EQE) and improved angular dependency than the device fabricated using the microcavity-based Ag electrode, it suffers from low color purity and severe efficiency roll-off. These drawbacks can be reduced by using an optimized multi-quantum well emissive layer (MQW EML). The CSE-based TADF-TEOLED with an MQW EML fabricated herein exhibits a high EQE (18.05%), high color purity (full width at half maximum ~ 59 nm), reduced efficiency roll-off (~ 46% at 1000 cd m−2), and low angular dependence. These improvements can be attributed to the synergistic effect of the CSE and MQW EML. An optimized transparent CSE improves charge injection and light outcoupling with low angular dependence, and the MQW EML effectively confines charges and excitons, thereby improving the color purity and EQE significantly. The proposed approach facilitates the optimization of multiple output characteristics of TEOLEDs for future display applications.

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Thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have attracted immense research interest because of the merits including 100% internal quantum efficiency and absence of heavy metals as dopants. However, great challenges, accomplishing the viewing angle characteristic, color shift, high efficiency, and color purity, simultaneously, remain [1, 2]. Herein, we propose a concept of combining the multiple quantum well-based emissive layer (MQW-EML) and multilayered transparent cathode to overcome these challenges. The Ag/WO3/Ag (AWA) multilayers (12 nm/65 nm/12 nm) was optimized based on optical simulation for use as a transparent cathode that exhibits high transmittance (~85% in the visible and blue wavelength region) and low sheet resistance of 5.3 Ω/sq on glass substrates. Compared to thin Ag-based TADF top-emitting OLEDs (TEOLEDS), the proposed AWA-based TEOLED having MQW-EMLs displayed a 40% improvement in external quantum efficiency (Figure. 1). Importantly, the device exhibited a lower angular dependence as well as a low full width at half maximum (FWHM) value (~60 nm), indicating high color purity. These improvements are attributed to the synergistic effect of the MQW-EML and AWA transparent cathode. The EML with quantum well structure effectively confines the charges and excitons, thereby significantly improving color purity and efficiency. On the other hand, the optimized AWA transparent cathode improved the charge injection and light coupling as well. Therefore, this work is expected to open an avenue for high efficient TADF-TEOLEDs, via the combination of the multilayered EML and transparent cathode. Figure 1