Non‐Covalent Postfunctionalization of Dye Layers on TiO2 — A Tool for Enhancing Injection in Dye‐Sensitized Solar Cells

We report on newly tailored dye layers, which were employed, on one hand, for covalent deposition and, on the other hand, for non‐covalently post‐functionalizing TiO2 nanoparticle films. Our functionalization concept enabled intermixing a stable covalent attachment of a first layer with a highly versatile and reversible hydrogen bonding through the Hamilton receptor–cyanuric acid binding motif as a second layer. Following this concept, we integrated step‐by‐step a first porphyrin layer and a second porphyrin/BODIPY layer. The individual building blocks and their corresponding combinations were probed with regard to their photophysical properties, and the most promising combinations were implemented in dye‐sensitized solar cells (DSSCs). Relative to the first porphyrin layer adding the second porphyrin/BODIPY layers increased the overall DSSC efficiency by up to 43 %. Layered approach to capture the sun: We present a sequential covalent/non‐covalent functionalization pathway for metal oxide nanoparticles. Initially a first ligand layer is attached via covalent anchoring of carboxylates, followed by a highly versatile addition of a second dye layer via hydrogen bonding. The resulting hierarchical hybrid architectures were investigated regarding their photophysical properties and finally implemented in sandwich‐type dye‐sensitized solar cell (DSSC) configurations, resulting in an efficiency increase of up to 43 %.