A DFT study on natural sensitizers with donor-π-acceptor architecture based on 1,7-diazaheptametine for applications in Dye-Sensitized Solar Cells (DSSC)

Nature offers a wide range of organic dyes with potential as sensitizers in DSSC technology. Among them, some natural dyes contain a 1,7-diazaheptamethine system, influencing their chromatic properties. In this investigation, we computationally analyzed 21 natural betalain dyes featuring a common structural moiety through Density Functional Theory calculations. Among them, eight dyes were classified under the betacyanin subfamily, while the remaining thirteen were attributed to the betaxanthin subfamily. These dyes were examined both in isolation and when bound to titanium dioxide (dye@TiO2). The betaxanthin subfamily showed more twisted geometries, while the betacyanin subfamily exhibited a smaller energy gap. All isolated dyes or dyes@TiO2 exhibit maximum absorption peaks within the visible region (350–700 nm), showcasing their light-capturing capacity. Stability, evidenced by negative adsorption energies, suggests the spontaneity of the adsorption process. Furthermore, our results indicate that the nature of bonding significantly influences the electronic properties of dye@TiO2 complexes. Collectively, these results underscore the importance of the 1,7-diazaheptamethine system in imparting color and structure to these dyes. Our thorough analysis, encompassing molecular interactions, geometric attributes—especially the configuration of donor groups—electronic properties, and absorption spectra, provides valuable insights into the potential applications and effectiveness of these dyes for incorporation in dye-sensitized solar cells (DSSC).