Theoretical study of zinc porphyrin-based dyes for dye-sensitized solar cells

A series of zinc porphyrin-based dyes (GY21, GY50-GY54) were theoretically investigated using density functional theory and time-dependent density functional theory to examine their performance as sensitizers in dye-sensitized solar cells. The intramolecular charge transfer (ICT) processes of dyes before and after binding (TiO2)9 cluster were fully analyzed by studying the electronic structures, frontier molecular orbitals, electronic transition processes and electron density variations of excited state and ground state. Key parameters associated with the efficiency of dyes were systematically analyzed on the basis of absorption spectra, driving force of electron injection (ΔGinject), and light-harvesting efficiency (LHE). The calculated results confirmed that GY50 had strong ICT character and LHE relative to GY21, which contributed to the high efficiency of GY50. Furthermore, introducing thiophene ring in the π-conjugated linker (GY52-GY54) decreased the HOMO-LUMO energy gaps, enhanced the absorption peaks in near infrared regions as well as the electronic coupling between the dyes and TiO2. This work is expected to provide useful information for designing efficient metal-free organic dyes for improving the performances of dye-sensitized solar cells (DSSCs).