Design principles for highly efficient organic light-emitting diodes

Abstract

Organic light-emitting diodes (OLEDs) show potential as the next-generation solidstate lighting technology. A major barrier to widespread adoption at this point is the efficiency droop that occurs for OLEDs at practical brightness (∼5000 cd∕m 2 ) levels necessary for general lighting. We highlight recent progress in highly efficient OLEDs at high brightness, where improvements are made by managing excitons in these devices through rational device design. General design principles for both white and monochrome OLEDs are discussed based on recent device architectures that have been successfully implemented. We expect that an improved understanding of exciton dynamics in OLEDs in combination with innovative device design will drive future development.

A multi-zoned white organic light-emitting diode with high CRI and low color temperature

“…It is worth noting that the current efficiency of the device with the 15 nm spacer is higher than that of device without a spacer layer. This 15 nm spacer layer, however, is larger than the Förster and Dexter energy transfer distance between the blue fluorophore and the phosphors 12 , and thus prevents a direct energy transfer from the blue singlet emitters to the adjacent green triplet emitters. This enhanced current efficiency is probably due to the carrier trapping by the doped triplet emission zones.…”

“…Now let’s focus on a device engineering method to reduce CCT, which is also a crucial parameter for WOLEDs. Partially based on above experimental findings and partially based on the fact that there is an efficient energy transfer between green and red emitters 12 , we doped Ir(ppy) 2 (acac) into the red emissive layer, i.e., using an intra-zone exciton harvesting scheme, to increase the red color component and thus decrease the CCT of the WOLED. The device is structured as: ITO/MoO 3 (1 nm)/CBP(20 nm)/CBP: Ir(piq) 2 (acac): Ir(ppy) 2 (acac)(3 wt.% R: x wt.% G,4 nm)/CBP: Ir(DMP) 3 (5 wt.%,4 nm)/CBP: Ir(ppy) 2 (acac)(7 wt.%,5 nm)/CBP(3 nm)/Bepp 2 : BCzVBi(50 wt.%,40 nm)/Bepp 2 (20 nm)/LiF(1 nm)/Al(100 m).…”

Exciton Dynamics of Photoexcited Pendant Porphyrin Polymers in Solution and in Thin Films

“…For organic materials, applications in organic photovoltaics (OPVs), organic light emitting diodes (OLEDs) and organic field effect transistors (OFETs) are being pursued vigorously. 1,6,7 Metalloporphyrins are particularly attractive as excitonically-active materials in photoexcited systems. 8,9 Their absorption spectra span the visible spectrum and can be extended well into the near infrared by appropriate synthetic modification, thereby providing excellent solar energy capture possibilities.…”

Efficient Blue Phosphorescent OLEDs with Improved Stability and Color Purity through Judicious Triplet Exciton Management

“…[30][31][32] These nonradiative and undesirable processes can result in severe emission efficiency roll-off and expedited device degradation. [33,34] However, it has been shown that careful management of polaron and exciton density inside the EML can significantly suppress the potential TPQ, TTA, and TPA processes. Following this concept, a device structure with a linear graded-doped EML was introduced to improve charge balance and extend the operational stability blue phosphorescent OLEDs employing Ir based emissive complexes.…”