Direct observation of interfacial charge transfer from silver to organic semiconductors

Abstract

The interface formation of the organic semiconductor CuPcF 4 with both polycrystalline and single crystalline silver substrates has been investigated using photoemission spectroscopy. We observe an electron transfer from the both the Ag substrates to the CuPcF 4 molecules at the interfaces. Furthermore we observe a change of the spectral shape of the highest occupied molecular orbital (HOMO) of CuPcF 4 as a function of the layer thickness. Especially for submono- and monolayers of CuPcF 4 on single crystalline Ag we resolve a double peak structure of the HOMO, which is discussed in detail. We compare the character of the charge transfer from the silver to the CuPcF 4-layer with the electron transfer from K to CuPcF 4 within a thick K-intercalated CuPcF 4-layer.