In situ interfacial analysis of evaporated potassium on the electroluminescent fluorene–thiophene copolymer

Abstract

X-ray photoelectron spectroscopy (XPS) was used to investigate the interface formation during in situ thermal evaporation of potassium on thin films of an electroluminescent conjugated polymer: poly[2,7-(9,9-dihexylfluorene)-co-alt-2,5-(decylthiophene)] (PFT). The chemical state and composition of the metal/polymer interfaces were studied as a function of the potassium coverage. Potassium was found to interact extensively with the bulk-adsorbed oxygen to form a layer of metal oxide at the K/PFT interface. Migration of the bulk-adsorbed oxygen to the surface occurred in response to the deposition of potassium onto the polymer. The changes in the S 2p lineshape suggested the formation of a thiolate species at low potassium coverages and also a sulphide species at higher metal coverages. The presence of charge transfer from the deposited potassium atoms to the carbon atoms of PFT suggested that the polymer had undergone n-type doping. The deposited potassium atoms also diffused into the subsurface region of the polymer film. Thus, the interface of K/PFT contained mainly the oxidized metal, metallic potassium and metal-polymer charge transfer complexes.

Spontaneous interlayer formation in OPVs by additive migration due to additive–metal interactions

“…The presence of PEG at the organic/metal interface is associated with the C-O peak at 286.6 eV in the XPS spectrum which is characteristic of the pristine PEG in the C1s XPS spectrum. 36 The peak at 286.6 eV binding energy could also be attributed to the interaction of Al atoms with bulk adsorbed oxygen and the polymer to form an Al-O-C complex, [37][38][39] or due to organic contaminants adsorbed on the sample's surface. The contribution of these species is represented in the intensity of the C-O peak in the XPS spectra of pristine P3HT lms with no PEG.…”

XPS characterisation of plasma treated and zinc oxide coated PET

“…Al-O-C species have been widely reported in works involving Al and Al 2 O 3 /polymer interfaces. The location of Al-O-C species in comparison with the neutral hydrocarbon (lower or higher) differed from one author to another [34,[59][60][61][62][63][64][65][66]. It is reasonable to suggest that there are two types of Metal-O-C species.…”

Elucidation of hierarchical metallophthalocyanine buffer layers in bulk heterojunction solar cells

“…It has been also reported that the Al metal can effectively transfer the electron to the conjugated polymer with the sulde species, and this feature makes it a potential cathode for polymeric electronics. 39 Another study 40 has also reported that Cu can react with P3HT and form sulde like species. These sulde like species can improve the solar cell performance.…”