Molecular design of corrole-based D-π-A sensitizers for dye-sensitized solar cell applications

Abstract

First principles calculations based on density functional theory (DFT) have been performed to design a new set of donor-corrole-bridge-acceptor type systems based on the gallium corroles for dye-sensitized solar cell applications. The design strategy for these systems is based on the benchmark studies done on the experimentally tested aluminum, gallium, and tin metallocorroles. Unfortunately, corrole analogues display poor light to current conversion efficiencies in spite of their desirable photophysical properties. Thus, improving the efficiency of corrole analogues has become a major challenge and ways to identify solutions to this is of outstanding fundamental importance. This study shows the lack of charge directionality toward anchoring group as plausible reason for the poor efficiencies of reported corrole systems, which enabled us to fine-tune the electronic and optical properties of new D-π-A type systems, COR1-COR4. The molecular geometries, electronic structure, and binding orientation of these systems on TiO₂ surface were investigated using DFT, TD-DFT, and PBC methods. When compared with the reported corroles, COR1-COR4 have a smaller band gaps, red-shifted absorption spectra with higher extinction coefficients (10⁵ M⁻¹ cm⁻¹) and improved nonlinear optical properties. Importantly, results revealed that these dyes bind with two-arm mode to TiO₂ surface and the density of states of the dye@TiO₂ elucidate strong coupling between the dyes and TiO₂ surface. We anticipate that the unique photophysical properties of these sensitizers will trigger the experimental efforts to yield a new generation of sensitizers based on corrole macrocyle.