In-Situ Compositional and Structural Analysis of Plastic Solar Cells

Bulk-heterojunction photovoltaic cells consisting of a photoactive layer of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and a C60 derivative, (1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene), (PCBM), sandwiched between an indium tin oxide (ITO) anode covered with poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and an aluminum cathode have been analyzed using transmission electron microscopy (TEM) and cryogenic Rutherford backscattering spectrometry (RBS) to assess the structural and elemental composition of these devices. TEM of cross sections of fully processed photovoltaic cells, prepared using a focused ion beam, provide a clear view of the individual layers and their interfaces. RBS shows that during preparation diffusion of indium into the PEDOT:PSS occurs while the diffusion of aluminum into the polymer layers is negligible. An iodinated C60 derivative (I-PCBM) was used to determine the concentration profile of this derivative in the vertical direction of a 100 nm active layer.