Theoretical investigation on co-sensitization of natural dyes for dye sensitized solar cells (dsscs) applications

This study reports the effect of co-sensitization of four dye molecules of 3,5,7-trihydroxy-2-(4-hydroxy-3-methoxyphenyl) chromen-4-one, 2-phenylchromen-4-one, betalains, and 2-descarboxy-betanidin from Senna singueana leaves, Begonia malabarica leaves, Bougainvillea glabra bract, and Celosia cristata flowers, respectively, for dye-sensitized solar cell applications. Co-sensitization was done by designing new dyes (D1, D2, and D3) by attaching molecules M2, M3, and M4 to molecule (M1). Moreover, the optimized molecular structures of the individuals and newly designed dyes were investigated through density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations by using the GAUSSIAN 09 software package. The results on newly designed dyes as sensitizers on DSSC showed a reduction in the HOMO-LUMO energy gap compared to the individual dyes. The newly co-sensitized dye molecules (D1, D2, and D3) were reported to have energy gap (E_g) of 2.29, 2.73, and 1.91 eV, respectively, which was very small compared to individual molecules (M1, M2, M3, and M4) with an energy gap of 2.88, 2.70, 3.12, and 2.34 eV respectively. Additionally, the maximum absorption spectra were extended up to 849.55 nm for newly dye D3 compared with 683.96 nm for the individual dye M4. Furthermore, the highest light harvesting efficiency (LHE) was changed from 0.5829 for individual dye (M1) up to 0.9582 for newly dye (D3). Thus, the energy band gap 〖(E〗g), the light harvesting efficiency (LHE), and absorption spectra of the newly designed dyes were enhanced compared to individual dyes. However, among the newly designed dyes, D3 showed the best properties compared to D1 and D2 for dye-sensitized solar cell applications.