Excitation Energy Dependent Charge Separation at Hole-Transporting Dye/TiO₂ Hetero Interface

Interfacial charge separation in hybrid solar cells depends on both the energetic alignment and electronic coupling between the inorganic and organic semiconducting materials at the hetero interface. In the present work, bilayer solar cells comprising the small molecular semiconducting dye TDCV-TPA (tris-(thienylene-vinylene)-triphenylamine) and dense titanium dioxide (TiO₂) films were investigated. The internal quantum efficiency and degree of photoluminescence quenching were found to be excitation energy dependent. The molecular interaction and interfacial energy level alignment was investigated using a combination of UV–vis and photoelectron spectroscopy (PES). Stationary and time-dependent density functional theory calculations were used to assign and distinguish between different experimentally determined molecular energy levels (PES) and electronic transitions (UV–vis). Photoelectron spectroscopy results suggest surface induced interactions of TDCV-TPA with TiO₂ involving the peripheral CN-groups of the molecule which would imply a favorable electronic coupling for photoinduced interfacial charge transfer. In an energy level diagram distinguishing between the different electronic transitions in the molecule, the differences in the thermodynamic driving force for electron injection from the excited states were found small. Therefore, it is suggested that the observed higher internal quantum efficiency at shorter wavelength can be rationalized by a more favorable driving force for the regeneration of holes created at the hetero interface at higher excitation energy

Electronic Structure of TiO₂/CH₃NH₃PbI₃ Perovskite Solar Cell Interfaces

The electronic structure and chemical composition of efficient CH₃NH₃PbI₃ perovskite solar cell materials deposited onto mesoporous TiO₂ were studied using photoelectron spectroscopy with hard X-rays. With this technique, it is possible to directly measure the occupied energy levels of the perovskite as well as the TiO₂ buried beneath and thereby determine the energy level matching of the interface. The measurements of the valence levels were in good agreement with simulated density of states, and the investigation gives information on the character of the valence levels. We also show that two different deposition techniques give results indicating similar electronic structures

Coadsorption of Dye Molecules at TiO₂ Surfaces: A Photoelectron Spectroscopy Study

The effects of coadsorbing the amphiphilic ruthenium-based dye Z907 (<i>cis</i>-bis­(isothio­cyanato)­(2,20-bipyridyl-4,40-dicarboxylato)­(4,40-dinonyl-20-bipyridyl)­ruthenium­(II)) with the coadsorbent DPA (<i>n</i>-decyl­phosphonic acid) and with the organic dye D35 ((<i>E</i>)-3-(5-(4-(bis­(2′,4′-dibutoxy­biphenyl-4-yl)­amino)­phenyl)­thiophen-2-yl)-2-cyano­acrylic acid) on mesoporous TiO₂ were investigated using photoelectron spectroscopy (PES). Z907 is expected to adsorb to the TiO₂ surface via the carboxylic acid groups. However, Z907 also shows signs of interacting with the TiO₂ via the sulfur of the thiocyanate groups, and this interaction is affected by both the addition of DPA and D35. DPA, when added, exchanges with Z907 at the TiO₂ surface, and each Z907 is replaced by six DPA molecules, but it does not affect the energy level alignment between Z907 and TiO₂ substantially. Adding D35 to Z907 induces changes in the adsorption configuration of Z907 by the means of suppressing the interaction of the thiocyanate ligands and the TiO₂ surface. The HOMO level of Z907 is shifted by the addition of D35. Coadsorbing Z907 with D35 thus gives changes at a molecular level, meaning that this is an example of collaborative sensitization

¹¹C and ¹⁸F Radiolabeling of Tetra- and Pentathiophenes as PET-Ligands for Amyloid Protein Aggregates

Three oligothiophenes were evaluated as PET ligands for the study of local and systemic amyloidosis <i>ex vivo</i> using tissue from patients with amyloid deposits and <i>in vivo</i> using healthy animals and PET-CT. The <i>ex vivo</i> binding studies revealed that all three labeled compounds bound specifically to human amyloid deposits. Specific binding was found in the heart, kidney, liver, and spleen. To verify the specificity of the oligothiophenes toward amyloid deposits, tissue sections with amyloid pathology were stained using the fluorescence exhibited by the compounds and evaluated with multiphoton microscopy. Furthermore, a <i>in vivo</i> monkey PET-CT study showed very low uptake in the brain, pancreas, and heart of the healthy animal indicating low nonspecific binding to healthy tissue. The biological evaluations indicated that this is a promising group of compounds for the visualization of systemic and localized amyloidosis