Haxpes technique applied to devices for the production and storage of energy

Résumé

The interest in Hard X-ray photoelectron spectroscopy (HAXPES) technique has grownrapidly in the past few years, due to the possibility to study the composition and electronicproperties of buried interfaces in the bulk and of multilayers, as well as, measure the core-levelbinding energy shifts of bulk atoms. At high electron kinetic energy, e.g. 15 keV, theinformation depth can reach several tens of nanometres1 and using the advantage of tuneablesynchrotron X-ray radiation the photoelectron kinetic energy and therefore the informationdepth can be changed and consequently electronic and compositional depth profiles can beobtained.2Our research group is devoted to the study of advanced materials for the production andstorage of energy. In this work we present the application of the HAXPES technique to differentmaterials, in bulk, layered samples and even in functional devices. The experiments werecarried out at the Spanish CRG SpLine beamline at the ESRF. 3 The first example is the analysisof the Zn anode in Zn/MnO2 ionic liquid based gel polymer electrolyte batteries, which havebeen discharged or charged reaching different states of charge. The second example deals aboutthe vertical segregation of PCBM within the active layers of standard and inverted organic solarcells, analyzing the influence of temperature and electrode composition of functional devices.Blends of P3HT and PCBM are the benchmark materials for the active layers of plastic solarcells. These experiments are a challenge since the photo-active layer of this kind of devices isnot a staking of two layers but it is a blend of two organic materials, where one material acts aselectron acceptor and the other as electron donor: their mixture creates a distributed “bulkheterojunction”. Nevertheless, the PCBM tends to aggregate and therefore destroy the pathneeded for n-type carrier transport; furthermore, the vertical segregation creates an inconvenientdepth profile for PCBM in standard architecture.