Molecular Interdiffusion between Stacked Layers by Solution and Thermal Annealing Processes in Organic Light Emitting Devices.
In organic light emitting devices (OLEDs), interfacial structures between multilayers have large impacts on the characteristics of OLEDs. Herein, we succeeded in revealing the interdiffusion in solution processed and thermal annealed OLEDs by neutron reflectometry. We investigated interfaces between a polymer under layer and small molecules upper layer. The small molecules diffused into the swollen polymer layer during the interfacial formation by the solution process, but the polymer did not diffuse into the small molecules layer. At temperatures close to the glass transition temperatures of the materials, asymmetric molecular diffusion was observed. We elucidated the effects of the interdiffusion on the characteristics of OLEDs. Partially mixing the interface improved the current efficiencies due to suppressed triplet-polaron quenching at the interface. Controlling and understanding the interfacial structures of the miultilayers will be more important to improve the OLED characteristics.
Department of Organic Device Engineering, Yamagata University , 4-3-16 Johnan, Yonezawa, Yamagata 992-8510, Japan.
Satoru
S
Ohisa
Department of Organic Device Engineering, Yamagata University , 4-3-16 Johnan, Yonezawa, Yamagata 992-8510, Japan.
Yong-Jin
YJ
Pu
Institute of Material Structure Science, High-Energy Accelerator Research Organization (KEK) , 203-1 Shirakata, Tokai, Naka 319-1106, Japan.
Norifumi L
NL
Yamada
Department of Polymer Science and Engineering, Yamagata University , 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan.
Go
G
Matsuba
Department of Organic Device Engineering, Yamagata University , 4-3-16 Johnan, Yonezawa, Yamagata 992-8510, Japan.
Junji
J
Kido
asymmetric diffusion; charge accumulation; interface; neutron reflectometry; poly-TPD; thermal diffusion