Theoretical (DFT and TDDFT) insights into the effect of polycyclic aromatic hydrocarbons on Monascus pigments and its implication as a photosensitizer for dye-sensitized solar cells

Monascus pigments (MPs) as natural food pigments which have been extensively used in food industries, specifically in China, Japan, and other countries of southeastern Asian. The optoelectronic properties of the MPs with polycyclic aromatic hydrocarbons (PAHs) units have been investigated by using density functional theory (DFT) and time-dependent (TDDFT) at B3LYP and the 6-31G(d) basis set. These properties include total energies, Fermi energy, work function, orbital distributions (HOMO, LUMO), the HOMO-LUMO gap, the maximum open circuit voltage, maximum wavelength absorption, electronic transition energies, and the oscillator strengths. These methods and calculation procedures not only encourage a profound understanding of the association between the optoelectronic properties and chemical structures of the molecules but also can be utilized to design new molecule structures. We investigated the influence of the PAHs into the MPs and studied the optoelectronic properties on all molecules. The results showed that the maximum absorption wavelengths for MPs-PAHs are within the visible light region. Therefore, these molecules provide good performance for the photovoltaic devices and solar cells applications. Significance: Our results showed that the total energy increase after addition of PAHs for MPs, this illustration that the molecules converted to more stability. The addition of PAHs can enhance HOMO, LUMO level which can upsurge reduce bandgap energy and also the faculty of electron injection. Where the bandgap energy lies in the range (2.242–3.012) eV. The λmax takes the values from 378.84 nm to 681.03 nm, where the lowest value for Ms. (S3) and highest for the Ms. (S1), where Ms. (S1) represents firsa t singlet excited state that is at about 681.03 nm but with a feeble absorption. We observed that the sturdy absorption peaks (Ms (S2), Ms-fluorene (S3), Ms-naphthalene (S3), and Ms-anthracene (S3)) are within the visible light region. These results of the dyes confirmation that these dyes are possible to be a perfect photosensitizer in solar cells.