Suitability of lithium doped electron injection layers for organic semiconductor lasers

Lithium doped 2,2′,2″-(1,3,5-benzenetryl)tris(1-phenyl)-1H-benzimidazol (TPBi) as electron injection layer in organic laser diodes is investigated. The optical material absorption of optimum doped Li:TPBi is as low as 300cm−1 at λ=600nm. Kelvin probe analysis demonstrates that thin layers (5nm) of Li:TPBi already enable efficient electron injection from low optical loss transparent conducting oxide contacts. Moreover, stable current densities of about 100A∕cm2 can be injected. The waveguide losses added due to these Li:TPBi layers can be as low as 3cm−1. These results present a major step towards electrically contacted, low-loss organic laser structures.