Dye-sensitized solar cells constitute a promising approach to sustainable and low-cost solar energy conversion. Their overall efficiency crucially depends on the effective coupling of the photosensitizers to the photoelectrode and the details of the dye's energy levels at the interface. Despite great efforts, the specific binding of prototypical ruthenium-based dyes to TiO2, their potential supramolecular interaction, and the interrelation between adsorption geometry and electron injection efficiency lack experimental evidence. Here we demonstrate multiconformational adsorption and energy level alignment of single N3 dyes on TiO2 anatase (101) revealed by scanning tunnelling microscopy and spectroscopy. The distinctly bound molecules show significant variations of their excited state levels associated with different driving forces for photoelectron injection. These findings emphasize the critical role of the interfacial coupling and suggest that further designs of dye-sensitized solar cells should target a higher selectivity in the dye-substrate binding conformations in order to ensure efficient electron injection from all photosensitizers.

The formation of extended two-dimensional metal-organic coordination networks (2D-MOCNs) showing high adaptability to surface step edges and structural defects is revealed by scanning tunneling microscopy. Rod-like 4,4'-di-(1,4-buta-1,3-diynyl)-benzoic acid (BDBA) and iron atoms assemble into extended 2D-MOCNs on Au(111) and Ag(100) surfaces. Independent from the chosen substrate and its surface symmetry the MOCN grows continuously over multiple surface terraces through mutual in-phase structure adaptation of network domains at step edges as well as on terraces. The adaptability of the MOCNs is mainly ascribed to the high degree of conformational flexibility of the butadiynyl functionality of the ligand. Despite their flexibility, the MOCNs exhibit considerable robustness against annealing at high temperatures. The findings show that mesoscale self-assembled functional architectures with a high degree of substrate error tolerance can be realized with metal coordination networks.

The present investigation of cyclopropylamine (CPA) plasma polymerization in pulsed and continuous wave radio frequency (RF) discharges leads to the proposition of conditions at which amine-rich films exhibit a good stability in contact with water. The analyses reveal complex structure of CPA plasma polymers containing hydrocarbon chains, primary and secondary amines, nitriles and possibly imines. The decomposition of the monomer in plasma is progressing with the composite parameter W/F (RF power over monomer flow rate) but, in pulsed discharges, it is possible to deposit the films with N/C ratio above 0.24 using higher monomer flow rate. At the optimized monomer flow rate the 280 nm thick film exhibits only 20% thickness loss after 48 h immersion in water and still contains about 5 at% of the NH x environment.

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