N-doping of pentacene by decamethylcobaltocene

We demonstrate n-type doping of pentacene with the powerful reducing molecule decamethylcobaltocene (CoCp∗2). Characterization of pentacene films deposited in a background pressure of CoCp∗2 by X-ray photoemission spectroscopy and Rutherford backscattering confirm that the concentration of incorporated donor molecules can be controlled to a level as high as 1%. Ultraviolet photoemission spectroscopy show Fermi level (EF) shifts toward unoccupied pentacene states, indicative of an increase in the electron concentration. A 1% donor incorporation level brings EF to 0.6 eV below the pentacene lowest unoccupied molecular orbital. The corresponding electron density of ∼1018 cm−3 is confirmed by capacitance–voltage measurements on a metal–pentacene–oxide–silicon structure. The demonstration of n-doping suggests applications of CoCp∗2 to pentacene contacts or channel regions of pentacene OTFTs. PACS 68.55.Ln · 79.60.Fr · 73.61.Ph