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 300 cm(-1) at lambda=600 nm. Kelvin probe analysis demonstrates that thin layers (5 nm) of Li:TPBi already enable efficient electron injection from low optical loss transparent conducting oxide contacts. Moreover, stable current densities of about 100 A/cm(2) can be injected. The waveguide losses added due to these Li:TPBi layers can be as low as 3 cm(-1). These results present a major step towards electrically contacted, low-loss organic laser structures. (c) 2007 American Institute of Physics.