Theoretical Insights into D-D-π-A Sensitizers Employing N-Annulated Perylene for Dye-Sensitized Solar Cells

This paper reports new D-D-π-A dyes based on N-annulated perylene, emphasizing the enhanced dye-to-semiconductor charge-transfer mechanism. A series of DFT calculations for new tPA-perylene-based dyes was conducted, starting from the systematic selection of DFT methods by reproducing the experimentally obtained properties of known perylene-based sensitizers. Accordingly, using the LC-ωPBE xc functional with 6-31+G(d) basis set for the time-dependent calculations of the excitation energies, a damping parameter of ω = 0.150 Bohr-1 was found to be most appropriate for dyes having spatial orbital overlap value of 0.21 ≤ ΛHL ≤ 0.38, while ω = 0.175 Bohr-1 is suitable for analogues with 0.43 ≤ ΛHL ≤ 0.57. Moreover, the mPWHandHPW91/6-31G(d) method gave high accuracy in GSOP calculations. The comparison between the properties of tPA-based donor groups has revealed that the semirigid tPA-based D4 unit is an effective donor group for perylene-based dye. Initial screening of the acceptor designs resulted in PLz4 dye with promising charge-transfer mechanism and highly favorable dye-TiO2 interaction based on the calculated dipole moment of the dye and dye-TiO2 complex. The attachment of the substituted-hydroacridine donor unit (D4) to PLz4 afforded a bathochromically shifted absorbance and improved molar absorptivity signifying its effective electron-donating ability. Among the D-D-π-A dyes, DP46 is expected to render a relatively high Voc and Jsc supported by the calculated optical properties, oxidation potentials, ionization potential, and electron affinity values.