Elucidating band-selective sensitization in iron(II) polypyridine-TiO2 assemblies

Area of Science:

• Materials Science
• Photochemistry
• Computational Chemistry

Background:

• Ruthenium(II) polypyridine dyes are effective photosensitizers in dye-sensitized solar cells (DSSCs).
• Iron(II) polypyridines offer a cheaper and less toxic alternative to ruthenium-based dyes.
• Understanding excited-state properties and interfacial electron transfer (IET) is crucial for DSSC efficiency.

Purpose of the Study:

• To investigate the ground and excited state properties of three Fe(II) polypyridine complexes using DFT and TD-DFT.
• To simulate the interfacial electron transfer (IET) between excited Fe(II) dyes and TiO2 nanoparticles using quantum dynamics.
• To elucidate the factors governing the efficiency of IET in Fe(II)-based DSSCs.

Main Methods:

• Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations.
• Quantum dynamics simulations for interfacial electron transfer (IET).
• Analysis of absorption spectra and excited-state properties of Fe(II) complexes.

Main Results:

• All three Fe(II) dyes exhibit two visible absorption bands, primarily metal-to-ligand charge transfer states.
• IET rates from lower-energy band excitation are slower than excited-state decay, making IET unlikely.
• Higher-energy absorption band excitation shows IET rates at or below 100 fs, indicating potential for efficient electron injection.

Conclusions:

• Fe(II) polypyridines show potential as DSSC photosensitizers, but efficient IET is band-selective.
• Excitation of higher-energy absorption bands is necessary for effective electron transfer to TiO2.
• Computational insights guide the design of improved Fe(II)-based DSSCs.