Use of a High Electron-Affinity Molybdenum Dithiolene Complex to p-Dope Hole-Transport Layers

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Abstract
Experimental and theoretical results are presented on the electronic structure of molybdenum tris[1,2-bis(trifluoromethyl) ethane-1,2-dithiolene] (Mo(tfd)3), a high electron-affinity organometallic complex that constitutes a promising candidate as a p-dopant for organic molecular semiconductors. The electron affinity of the compound, determined via inverse photoemission spectroscopy, is 5.6 eV, which is 0.4 eV larger than that of the commonly used p-dopant F4-TCNQ. The LUMO level of Mo(tfd)3 is calculated to be delocalized over the whole molecule, which is expected to lead to low pinning potential. Efficient p-doping of a standard hole transport material (α-NPD) is demonstrated via measurements of Fermi level shifts and enhanced conductivity in α-NPD:1% Mo(tfd)3. Rutherford backscattering measurements show good stability of the three-dimensional Mo(tfd)3 molecule in the host matrix with respect to diffusion.