Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV16)
Publication date: 28th March 2016
Organic materials are becoming increasingly widely used in a diverse range of optoelectonics. The myriad structural permutations and the potential for low cost manufacture provide a powerful research drive. Whilst efficiencies of organic photovoltaics have steadily risen, there is a concern that the lifetimes of current materials may limit their potential commercial exploitation. We examine the photodegradation in air of the commonly used phenyl C61 butyric acid methyl ester (PCBM) molecule. More specifically, we demonstrate the use of novel argon gas cluster ion sources (GCIS) in combination with analytical techniques including X-ray photoelectron spectroscopy (XPS) to quantify this.
Depth profiling is a powerful technique that has long been used for studying thin films or surface chemistry changes in inorganic systems. However the technique has traditionally suffered significant draw backs when studying the organic materials or fragile inorganic systems commonly used in emerging photovoltaics. The incident Ar+ beam in combination with ultrahigh vacuum conditions would typically induce catastrophic experimental artefacts. One such artefact causes chemical reduction of materials during the etching phase of experiment. This ultimately results in a loss of stoichiometric data in the bulk, and is particularly damaging for fragile systems such as organics or Pb(II) based materials.
Here we demonstrate that novel argon cluster GCIS eliminates such artefacts to allow quantitative chemical analysis of a whole 100 nm organic film. Photo oxidation of PCBM films in air is utilized as a model system to demonstrate this. Both surface oxidation and penetration of oxidation into the bulk film are monitored through to the underlying transparent conductive oxide substrate. Such analyses are broadly applicable to a wide range of challenges in OPV and perovskite materials such as segregation, surfactant action or catalysis function. In conclusion, we demonstrate the use of the novel GCIS – XPS technique to study the photo-oxidation of PCBM and the degree of oxidation measured quantitatively.