Imaging the Ultrafast Photoelectron Transfer Process in Alizarin-TiO2

Abstract

In this work, we adopt a quantum mechanical approach based on time-dependent density functional theory (TDDFT) to study the optical and electronic properties of alizarin supported on TiO 2 nano-crystallites, as a prototypical dye-sensitized solar cell. To ensure proper alignment of the donor (alizarin) and acceptor (TiO 2 nano-crystallite) levels, static optical excitation spectra are simulated using time-dependent density functional theory in response. The ultrafast photoelectron transfer from the dye to the cluster is simulated using an explicitly time-dependent, one-electron TDDFT ansatz. The model considers the δ-pulse excitation of a single active electron localized in the dye to the complete set of energetically accessible, delocalized molecular orbitals of the dye/nano-crystallite complex. A set of quantum mechanical tools derived from the transition electronic flux density is introduced to visualize and analyze the process in real time. The evolution of the created wave packet subject to absorbing boundary conditions at the borders of the cluster reveal that, while the electrons of the aromatic rings of alizarin are heavily involved in an ultrafast charge redistribution between the carbonyl groups of the dye molecule, they do not contribute positively to the electron injection and, overall, they delay the process.

An open‐source framework for analyzing N‐electron dynamics. I. Multideterminantal wave functions

“…A widespread quantity for the visual representation of electronic motions in molecular systems is the time‐dependent one‐electron density . It remains a useful tool to characterize the correlated electron dynamics from multideterminant wave functions of the form eq.…”

Exploring the relevance of thiophene rings as bridge unit in acceptor‐bridge‐donor dyes on self‐aggregation and performance in DSSCs

“…As already commented above, the dyes were bounded to the semiconductor through a bidentate bond with the carboxylic acid group of the donor. Here, the model of TiO 2 with 15 units used in this investigation has been suggested in former reports as optimal for studying the electronic and energetic features of the adsorbed systems . The results obtained with this cluster are as good as those obtained with the cluster with 38 TiO 2 units at a reasonable computational cost for full QM calculations …”

An open‐source framework for analyzing N‐electron dynamics. II. Hybrid density functional theory/configuration interaction methodology

“…Therefore, we perform a TURBOMOLE calculation with the B3LYP hybrid functional and the def2‐SVP basis set at the equilibrium geometry of alizarin. This setup has been previously proven to yield accurate results for the electronic and spectroscopic properties of such systems . The computed absorption spectrum is depicted in Figure a along with the experimentally observed absorption band of free alizarin (dashed black line).…”