X-ray Studies of Novel Photoactive Elements for Solar Cells
Morphology and lattice structure of photoactive materials are key factors in determining the efficiency of solar devices. We present X-ray scattering studies of four types of photoactive systems with novel photoactive elements: perylene monoimide based nanoribbons for solar-to-fuel conversion devices, tetrathienoacene based organic dyes for dye sensitized solar cells, layered lead perovskites for solar cells and fluorinated small molecule donor for ternary bulk heterojunction solar cells. We perform wide angle X-ray scattering measurements of perylene monoimide based nanoribbons, both in solution and deposited dry film, and develop formalism for interpreting obtained X-ray scattering patterns. This generally applicable method reproduces the measured diffraction patterns, including the asymmetric line-shapes for the Bragg reflections and yields the molecular packing arrangement within a 2D crystal structure and how it alters upon chemical modification of the constituting molecules. X-ray study of phase transition of n-propyl perylene monoimide nanostructure is discussed. X-ray reflectivity technique is used to study the monolayer morphology of tetrathienoacene based dyes deposited on titanium dioxide surface. The latter serves as an electrode in dye sensitized solar cells. Through atomic layer deposition a model surface of titanium oxide is fabricated, and organic dye monolayer deposited on it from organic solution. Analysis of X-ray reflectivity measurements expose the transformations monolayer films undergo upon alterations of backbone structure and modifications of hydrophobic alkyl chains which designed to prevent recombination and improve solubility. The results for molecular packing and molecular footprint correlate well with the measured efficiency and other characteristics of solar cells built with these dyes.
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