Decamethylcobaltocene as an efficient n-dopant in organic electronic materials and devices

n-Doping of copper phthalocyanine (CuPc), which has an electron affinity (EA) of 3.52 eV, by decamethylcobaltocene (DMC) is demonstrated. DMC has a remarkably low solid-state ionization energy (IE) of 3.3 eV, as measured by ultra-violet photoemission spectroscopy (UPS). Further UPS measurements show a large 1.4 eV upward shift of the Fermi-level within the single particle gap of CuPc between the p- and n-doped films. n-Doping is also confirmed by current-voltage (I-V) measurements, which show a 10⁶-fold increase in current density due to improved electron injection and enhanced conductivity of the bulk film. An organic p-i-n CuPc homojunction is also fabricated using F₄-TCNQ and DMC as p- and n-dopants, respectively. Current-voltage characteristics demonstrate excellent rectification with a turn on voltage of approximately 1.3 eV, which is consistent with the built-in voltage measured by UPS and capacitance-voltage (C-V) measurements.