Gold work function reduction by 2.2eV with an air-stable molecular donor layer

Abstract

Ultraviolet photoelectron spectroscopy was used to investigate neutral methyl viologen ($1,1^{\prime }$ -dimethyl-$1\mathrm{H},1^{\prime }\mathrm{H}\text{-}[4,4^{\prime }]\text{bipyridinylidene}$ , MV0) deposited on Au(111). As a result of molecule-to-metal electron transfer, the work function of Au(111) was decreased from $5.50\text{to}3.30\mathrm{eV}$ . The energy levels of electron transport layers deposited on top of modified Au surfaces were shifted to higher binding energies compared to layers on pristine Au, and the electron injection barrier was reduced by $0.80\mathrm{eV}$ for tris(8-hydroxyquinoline)aluminum $\left(\mathrm{Al}{\mathrm{q}}_3\right)$ and by $0.65\mathrm{eV}$ for ${\mathrm{C}}_{60}$ . The air-stable donor MV0 can thus be used to facilitate electron injection into organic semiconductors even from high work function metals.