In this work, molecular tuning of metal xanthate precursors is shown to have a marked effect on the heterojunction morphology of hybrid poly(3-hexylthiophene-2,5-diyl) (P3HT)/CdS blends and, as a result, the photochemical processes and overall performance of in situ fabricated hybrid solar cells. A series of cadmium xanthate complexes is synthesized for use as in situ precursors to cadmium sulfide nanoparticles in hybrid P3HT/CdS solar cells. The formation of CdS domains is studied by simultaneous GIWAXS (grazing incidence wide-angle X-ray scattering) and GISAXS (grazing incidence small-angle X-ray scattering), revealing knowledge about crystal growth and the formation of different morphologies observed using TEM (transmission electron microscopy). These measurements show that there is a strong relationship between precursor structure and heterojunction nanomorphology. A combination of TAS (transient absorption spectroscopy) and photovoltaic device performance measurements is used to show the intricate balance required between charge photogeneration and percolated domains in order to effectively extract charges to maximize device power conversion efficiencies. This study presents a strong case for xanthate complexes as a useful route to designing optimal heterojunction morphologies for use in the emerging field of hybrid organic/inorganic solar cells, due to the fact that the nanomorphology can be tuned via careful design of these precursor materials.
Nickel sulfide thin films and nanocrystals stabilized with oleylamine ligands are prepared from two different nickel xanthates as single-source precursors, which decompose at approx. 180°C, and are thereby converted into nickel sulfide. These nickel xanthates comprise branched alkyl moieties allowing the choice of a wide range of nonpolar organic solvents for the processing to nickel sulfide thin films as well as to nanoparticles. The crystal structures of both compounds show a typical square-planar coordination of the sulfur atoms of both xanthates to the nickel central atom. The thermal decomposition via the Chugaev reaction forming nickel sulfide was studied by thermal gravimetric analysis showing the reaction taking place at about 180°C. Consequently, by thermally converting spin-coated metal xanthate films directly on the substrates in the solid state, thin films consisting of hexagonal nickel sulfide are formed. If the nickel xanthates are heated in an oleylamine solution, oleylaminecapped nickel sulfide nanocrystals are obtained, exhibiting hexagonal NiS as main phase and Ni 3 S 4 as secondary phase. This is also reflected in a sulfur-rich composition of the synthesized nickel sulfide nanocrystals as observed from TEM-EDX analyses.
Different coligands on zinc xanthate complexes significantly influence the thermal decomposition mechanism in the conversion process towards nanocrystalline zinc sulfide.
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