White organic light-emitting diodes with ultra-thin mixed emitting layer

T. Jeon; S. Forget; S. Chenais; B. Geffroy; D. Tondelier; Y. Bonnassieux; E. Ishow

doi:10.1117/12.908156

17 February 2012 White organic light-emitting diodes with ultra-thin mixed emitting layer

T. Jeon, S. Forget, S. Chenais, B. Geffroy, D. Tondelier, Y. Bonnassieux, E. Ishow

Proceedings Volume 8258, Organic Photonic Materials and Devices XIV; 82580G (2012) https://doi.org/10.1117/12.908156
Event: SPIE OPTO, 2012, San Francisco, California, United States

Abstract

White light can be obtained from Organic Light Emitting Diodes by mixing three primary colors, (i.e. red, green and blue) or two complementary colors in the emissive layer. In order to improve the efficiency and stability of the devices, a host-guest system is generally used as an emitting layer. However, the color balance to obtain white light is difficult to control and optimize because the spectrum is very sensitive to doping concentration (especially when a small amount of material is used). We use here an ultra-thin mixed emitting layer (UML) deposited by thermal evaporation to fabricate white organic light emitting diodes (WOLEDs) without co-evaporation. The UML was inserted in the hole-transporting layer consisting of 4, 4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl (α-NPB) instead of using a conventional doping process. The UML was formed from a single evaporation boat containing a mixture of two dipolar starbust triarylamine molecules (fvin and fcho) presenting very similar structures and thermal properties and emitting in complementary spectral regions (orange and blue respectively) and mixed according to their weight ratio. The composition of the UML specifically allows for fine tuning of the emission color despite its very thin thickness down to 1 nm. Competitive energy transfer processes from fcho and the host interface toward fvin are key parameters to control the relative intensity between red and blue emission. White light with very good CIE 1931 color coordinate (0.34, 0.34) was obtained by simply adjusting the UML film composition.

Citation Download Citation

T. Jeon, S. Forget, S. Chenais, B. Geffroy, D. Tondelier, Y. Bonnassieux, and E. Ishow "White organic light-emitting diodes with ultra-thin mixed emitting layer", Proc. SPIE 8258, Organic Photonic Materials and Devices XIV, 82580G (17 February 2012); https://doi.org/10.1117/12.908156

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KEYWORDS

Organic light emitting diodes

Molecules

Interfaces

Absorption

Doping

Aluminum

CIE 1931 color space

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