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Loss in efficiency of perovskite solar cells may be caused by structural and/or chemical alterations of the complex layered system. As these changes might take place either in the bulk and/or on the surface of the stratified material, analytical tools addressing both key issues are selected and combined. SEM/EDX combined with XPS were chosen as appropriate methodical approach to characterise perovskite laboratory cells in depth and complementary on top, before and after light exposure. The layered perovskite system investigated here is based on glass covered with fluorine doped tin oxide (FTO), followed by three porous thin films of TiO2, ZrO2 and a thick monolithic carbon. The TiO2 film is subdivided into a dense layer covered by a porous one constituted of nanoparticles with a truncated bipyramidal shape. This layered system serves as the matrix for the perovskite. After infiltration of perovskite solution and annealing, EDX
spectral maps on cross-sections of the specimen have been measured. The distribution of relevant
elements – Si, Sn, Ti, Zr and C – correlates conclusively with layers visible in the acquired SEM images. Lead and iodine are distributed throughout the porous layers C, ZrO2 and TiO2. In a SEM micrograph taken of the cross-section of a sample after illumination, the glass substrate and all layers FTO, TiO2, ZrO2 as well as C are clearly identified. By EDX it was found that several weeks of ambient daylight did not change significantly the qualitative elemental composition of lead and iodine throughout the solar cell system. It was confirmed with EDX that nanoparticles identified in high-resolution SEM micrographs contain mainly Pb and I, indicating these to be the perovskite
crystals. However, a time-dependent compositional and chemical altering was observed with XPS for the near-surface region of the outermost ~10 nm after two months of illumination.
Organic surface modification and analysis of TiO2 nanoparticles for self-assembly in multiple layers
(2017)
Parameters of TiO2 coatings can greatly influence their final performance in largescale applications such as photocatalytic measurements, orthopedic and/or dental prostheses, cell cultures, and dye-sensitized solar cells. From different film deposition procedures, self-assembly of TiO2 NPs in multiple layers was selected for systematic characterization. EDX, AES and ToF-SIMS analysis have been carried out in order to evaluate the functionalization of several types of TiO2 NPs differing in size, shape and surface area.