This presentation focuses on the use of soft and hard X-ray photoelectron spectroscopy for experimental understanding and design of interfaces in mesoscopic materials used for energy conversion. In particular the presentation contain investigations on electronic structure and chemical composition of perovskite structures (e.g. CH3NH3PbI3) and molecular materials (e.g. Spiro-OMeTAD hole-conductor) deposited onto mesoporous oxides used in solar cells and Li-ion batteries.
The efficiency of the conversion process in these systems is largely dependent on the properties of the interfacial region including atomic and molecular organization as well as orbital composition and energy matching between the materials. Insight into electronic structure of the interface is therefore crucial in order to understand and optimize the function. X-ray based techniques such as photoelectron spectroscopy (PES) are powerful for obtaining such information at an atomic level due to the possibility for element specificity. This contribution reviews some of our recent synchrotron based PES developments for understanding the material interfaces between molecular as well as inorganic materials. Specifically how PES can be used as both a surface and a near surface technique.Specifically it will be shown how a combination of soft and hard X-ray photoelectron spectroscopy can be used to experimentally understand the molecular orbital structure in molecular materials, the valence electronic structure of CH3NH3PbI3 and similar compounds as well as oxide intermixing in conducting thin films.