Journal
PHYSICAL REVIEW APPLIED
Volume 17, Issue 5, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevApplied.17.L051002
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Funding
- US Department of Energy (DOE) EERE SSL program [DE-EE0008717]
- Robert and Beverly Sundahl Fellowship
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The research shows that by coevaporating a common electron-transport material with medium-density polyethylene, spontaneous orientational polarization in organic light-emitting diodes can be dramatically reduced, leading to improvements in operating voltage, external quantum efficiency, and device lifetime. These enhancements stem from reduced exciton-polaron annihilation in the emissive layer, suggesting a functional relationship between EQE and lifetime that can quantify degradation rates induced by annihilation in the device.
Spontaneous orientational polarization (SOP) in the electron-transport layer (ETL) of organic light-emitting diodes (OLEDs) is increasingly recognized as a key factor influencing their performance. Here, we show that SOP is dramatically reduced in the common electron-transport material 2,2',2 ''-(1,3,5-benzinetriye-tris(1-phenyl-1-H-benzimidazole) by coevaporating it together with medium-density polyethylene. Eliminating SOP from the ETL of blue fluorescent OLEDs in this manner reduces their operating voltage by 0.5 V, increases their external quantum efficiency (EQE) by 30%, and leads to a three-fold increase in device lifetime. We show that the EQE and lifetime improvements both originate from reduced exciton-polaron annihilation in the emissive layer, and that this leads to a functional relationship between the two quantities that can be used to quantify the rate of annihilation-induced degradation in the device. These results highlight a substantial opportunity to improve OLED performance by controlling SOP through semiconductor dilution and suggest that this capability can be used to systematically isolate and understand exciton-polaron degradation in the pursuit of stable blue OLEDs.
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