POS5-1395
Chalcogen Atom Substitution in Organic Semiconductors for Developing Efficient and Stable Blue Phosphorescent OLEDs
When and Where
Nov 30, -0001
00:00 - 00:00
Presenter(s)
Yongjun Kwon (Ulsan National Institure of Science and Technology)
Co-Author(s)
Abstract
The operational stability of blue phosphorescent organic light-emitting diodes (PhOLEDs) is considered as one of the key challenges, largely due to the high driving voltage (Vd) required for blue electroluminescence. This causes charge imbalance and triplet exciton leakage, leading to efficiency roll-off and rapid degradation. Interfacial layers with high triplet energy (T₁), especially electron-blocking layers (EBLs), have been widely introduced to improve the device performance and stability through triplet exciton confinement, but their wide energy bandgap can rather increase Vd and accelerate device degradation.
In our previous study, a molecular design strategy of ortho-linked electron-blocking material (EBM) with high T₁ and herringbone-like molecular packing successfully improved device stability by significantly decreasing Vd.[1] Building on this work, we introduce a strategy of chalcogen atom substitution that employs intermolecular chalcogen bonding (σ-hole interaction) to precisely control molecular packing of EBMs. The σ-hole is a region of low electron density along the extension of a chalcogen covalent bond that enables directional noncovalent interactions with electron-rich sites (lone pairs or negative electrostatic potential) and promotes denser intermolecular packing.
EBMs with different chalcogen substitutions (O, S and Se) are designed and synthesized. Grazing-incidence wide-angle X-ray diffraction (GIWAXD) analysis reveals shortened π–π stacking distances in thin films, while photophysical measurements confirm that the energy levels including high T₁ are maintained upon chalcogen atom substitution. Therefore, enhanced hole mobility through improved molecular packing by chalcogen atom substitution is expected, ultimately improving the performance and stability of blue PhOLEDs.
In our previous study, a molecular design strategy of ortho-linked electron-blocking material (EBM) with high T₁ and herringbone-like molecular packing successfully improved device stability by significantly decreasing Vd.[1] Building on this work, we introduce a strategy of chalcogen atom substitution that employs intermolecular chalcogen bonding (σ-hole interaction) to precisely control molecular packing of EBMs. The σ-hole is a region of low electron density along the extension of a chalcogen covalent bond that enables directional noncovalent interactions with electron-rich sites (lone pairs or negative electrostatic potential) and promotes denser intermolecular packing.
EBMs with different chalcogen substitutions (O, S and Se) are designed and synthesized. Grazing-incidence wide-angle X-ray diffraction (GIWAXD) analysis reveals shortened π–π stacking distances in thin films, while photophysical measurements confirm that the energy levels including high T₁ are maintained upon chalcogen atom substitution. Therefore, enhanced hole mobility through improved molecular packing by chalcogen atom substitution is expected, ultimately improving the performance and stability of blue PhOLEDs.
