Dye-Sensitized Solar Cells (DSSCs) and Dye-Sensitized Photoelectrochemical Cells (DSPECs) have attracted much interest in recent years for solar energy conversion. To fulfil the potential of these devices, their chemical stability and efficiency should be understood more clearly. Since the efficiency is closely linked to the crucial process of photoinduced charge separation and charge recombination, the energy levels of the molecular components and interfaces need to align optimally. Computational studies provide insight into these fundamental processes and suggest design principles. However, given the complexity of the system, a good compromise between accuracy and computational cost has to be found. Researchers from Leiden University and the VU University Amsterdam used Density Functional based Tight Binding (DFTB) and an extended Hückel approach to model photoinduced charge separation and electron injection from organic dyes into a TiO2 electrode.
A fully solvated dye-sensitized photoanode system (see picture) was simulated with SCC-DFTB(ti-org-0-1) molecular dynamics, to investigate the effect of nuclear dynamics and explicit solvation on the photoinduced electron injection process. Different core extended naphthalene diimide (NDI) based dyes were studied. For reliable HOMO and LUMO energies, extended Hückel Hamiltonian parameters were optimized based on delta SCF and TDDFT calculations with ADF (B3LYP-D3-BJ/DZP, COSMO). The calculated redox potentials of NDI-based dyes with this approach compare well to experiment, and were therefore used for synthetically unknown species.
The nuclear dynamics and trajectory sampling are crucial for describing the injection process, while explicit solvation is important in exploring the correct conformational space during the molecular dynamics.
J. P. Menzel, A. Papadopoulos, J. Belić, H. J. M. de Groot, L. Visscher, F. Buda, Photoinduced Electron Injection in a Fully Solvated Dye-Sensitized Photoanode: A Dynamical Semiempirical Study, J. Chem. Phys. C 2020 (ASAP).Key conceptsADF charge transfer DFTB DSSCs materials science organic electronics