Photoinduced processes in nanoassemblies and on surfaces

Nanocrystal quantum dots (NQDs) are an exciting class of materials that offer a unique possibility to tailor their optoelectronic properties due to their size dependent behavior originating from quantum confinement of charge carriers. This particular aspect imparts on them significantly property differences compared to their bulk counterparts, providing numerous important opportunities in the field of nanoscale semiconductor science. One of the biggest challenges from an application point of view is to increase their processability (both in solid state and in solution phase) and to interface them with a matrix, or molecules that are able to provide electronic energy or charges. Various approaches have been used and adapted in this regard such as incorporating these materials in a polymer matrix (for OLED applications) or combining them with mesoporous TiO2 (for photovoltaic applications). \ud Our approach is to functionalize these materials with (electro)luminescent metal complexes based on Ir(III) and Ru(II) metal ions, coordinated with ligands possessing appropriate anchoring groups that will interact with the surface of the quantum dot. These metal complexes are chosen as they are redox active chromophores with very rich photophysics (particularly emissive triplet states and electroluminescence) and electrochemistry (excellent charge transfer properties) and hence are excellent candidates for optoelectronic applications. By combining these two different classes of materials, one could fabricate a bifunctional nanoassembly with a possibility to control the band gap properties of both the constituent fragments synergistically. Understanding of basic photophysical processes that occur in such materials are of quintessential importance for the development of practical applications and further design. This thesis deals with the design of assemblies incorporating quantum dots and organic or organometallic chromophores. The photoinduced processes in such organic-inorganic hybrid nanosystems are investigated

Luminescent acetylthiol derivative tripodal osmium(II) and iridium(III) complexes: Spectroscopy in solution and on surfaces

Luminescent Os(II) and Ir(III) complexes containing a tripodal-type structure terminalized with three thiol derivatives are described. The tripod is introduced through derivatization, with a rigid spacer, of a phenanthroline ligand coordinated to the metal ion, and the entire structure possesses axial geometry. The geometry of the complexes combined with the three anchoring sites, the thiol groups, allows the complexes to adopt an almost perpendicular arrangement to the surfaces and the formation of a well-packed monolayer on Au substrates. The photophysical and electrochemical behavior of the complexes is studied in solution and on surfaces. Furthermore, a self-assembled monolayer (SAM) of Os(II) complexes on an ultraflat Au surface is used to fabricate a metal-molecule-metal junction with Au and In Ga eutectic as electrodes. The Os(II) SAM in the tunneling junction exhibits rectification behavior which is opposite in direction to that which we have previously shown for Ru(II) SAM

Luminescent acetylthiol derivative tripodal osmium(II) and iridium(III) complexes: Spectroscopy in solution and on surfaces

Luminescent Os(II) and Ir(III) complexes containing a tripodal-type structure terminalized with three thiol derivatives are described. The tripod is introduced through derivatization, with a rigid spacer, of a phenanthroline ligand coordinated to the metal ion, and the entire structure possesses axial geometry. The geometry of the complexes combined with the three anchoring sites, the thiol groups, allows the complexes to adopt an almost perpendicular arrangement to the surfaces and the formation of a well-packed monolayer on Au substrates. The photophysical and electrochemical behavior of the complexes is studied in solution and on surfaces. Furthermore, a self-assembled monolayer (SAM) of Os(II) complexes on an ultraflat Au surface is used to fabricate a metal–molecule–metal junction with Au and In Ga eutectic as electrodes. The Os(II) SAM in the tunneling junction exhibits rectification behavior which is opposite in direction to that which we have previously shown for Ru(II) SAMs.Chemistry and Chemical Biolog

Direct observation of charge generating regions and transport pathways in bulk heterojunction solar cells with asymmetric electrodes using near field photocurrent microscopy

We present a versatile method to examine the donor- acceptor based bulk heterojunction structures using a combination of structural, optical and optoelectronic contrast. The technique relies on current- contrast- optical scanning microscopy on asymmetric photovoltaic device structures with the electrodes extending in orthogonal directions to form a cross- type structure which provides a near- field access for the incident light beam. The method was used to follow changes with annealing and different ratios of the Si- PCPDTBT:PC71BM system, where the correlation between the changes in the morphology and charge carrier generation leading to photocurrent was clearly established. The general viewpoint of increasing heterogeneity between two components and continuous pathways in the entire photovoltaic layer upon thermal annealing are clearly evident from the high resolution optical and current contrast images. Fourier analysis of the images was used to extract the relevant length scales which prevail in these binary mixtures and quantify the changes upon thermal annealing

Luminescent acetylthiol derivative tripodal osmium(II) and iridium(III) complexes: Spectroscopy in solution and on surfaces

Luminescent Os(II) and Ir(III) complexes containing a tripodal-type structure terminalized with three thiol derivatives are described. The tripod is introduced through derivatization, with a rigid spacer, of a phenanthroline ligand coordinated to the metal ion, and the entire structure possesses axial geometry. The geometry of the complexes combined with the three anchoring sites, the thiol groups, allows the complexes to adopt an almost perpendicular arrangement to the surfaces and the formation of a well-packed monolayer on Au substrates. The photophysical and electrochemical behavior of the complexes is studied in solution and on surfaces. Furthermore, a self-assembled monolayer (SAM) of Os(II) complexes on an ultraflat Au surface is used to fabricate a metal–molecule–metal junction with Au and In Ga eutectic as electrodes. The Os(II) SAM in the tunneling junction exhibits rectification behavior which is opposite in direction to that which we have previously shown for Ru(II) SAMs