Understanding Physico-Chemical Aspects in the Depth Profiling of Polymer:Fullerene Layers

Layers composed of binary blends of a polymer and a fullerene derivative are at the heart of bulk heterojunction organic photovoltaic cells. The efficiency and stability of these devices critically depend on the distribution of the polymer and fullerene materials within the blend layer. Whereas time-of-flight secondary ion mass spectrometry, particularly in combination with cluster ion beams, has frequently been used to probe similar organic materials, the quantification of the results is often missing due to a lack of understanding of all the parameters influencing the measurement results. This study contributes to improved quantification by exploring the role of the bulk composition and interfacial material on parameters such as sputtering yield, mass fragmentation, and ionization. We show that the argon cluster sputtering yields of these materials may be described by two widely acknowledged sputtering yield relationships. Their fitting parameters depend on the layer composition in a manner that is cons...