Realization of high-efficiency fluorescent organic light-emitting diodes with low driving voltage

Amin Salehi,Felix N Castellano,Dong-Hun Shin,Christopher Papa,Anh Thy Bui,Liping Zhu,Franky So,Chen Dong

doi:10.1038/s41467-019-10260-7

Amin Salehi, Felix N Castellano + Show 6 more

Open Access

https://doi.org/10.1038/s41467-019-10260-7

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Journal: Nature Communications	Publication Date: May 24, 2019
Citations: 78	License type: open-access

Affiliation: North Carolina State University

Abstract

It is commonly accepted that a full bandgap voltage is required to achieving efficient electroluminescence (EL) in organic light-emitting diodes. In this work, we demonstrated organic molecules with a large singlet-triplet splitting can achieve efficient EL at voltages below the bandgap voltage. The EL originates from delayed fluorescence due to triplet fusion. Finally, in spite of a lower quantum efficiency, a blue fluorescent organic light-emitting diode having a power efficiency higher than some of the best thermally activated delayed fluorescent and phosphorescent blue organic light-emitting diodes is demonstrated. The current findings suggest that leveraging triplet fusion from purely organic molecules in organic light-emitting diode materials offers an alternative route to achieve stable and high efficiency blue organic light-emitting diodes.

Highlights

We demonstrate that organic molecules with a large singlettriplet splitting which exhibit P-type delayed fluorescence can form triplet excitons via direct charge injection, and result in efficient EL at sub-bandgap voltages close to their triplet energy without the presence of any exciplex states
Since there is no hole transport layer (HTL) or electron transport layer (ETL) presented in the device, these results clearly show that triplet excitons are formed under low voltage
This work demonstrated that triplet excitons can form under low driving voltage around the triplet exciton energy of the materials and subsequently generate singlet excitons through triplet fusion (TF) process and emit light

Summary

Introduction

We demonstrate that organic molecules with a large singlettriplet splitting which exhibit P-type delayed fluorescence can form triplet excitons via direct charge injection, and result in efficient EL at sub-bandgap voltages close to their triplet energy without the presence of any exciplex states. Similar to the BCzVBi single-layer device, the photocurrent versus the current density of the CzPA device shows quadratic behavior for the low current region and linear behavior for the high current region, and the transient EL of the device displays microsecond delayed fluorescence, indicative of emission originating from triplet fusion.

Results

Conclusion