The molecular modification and the effects of the gas and water media on the ability of some flavonoids as the photosensitizers in the natural dye-sensitized solar cells (NDSSCs) were theoretically investigated. According to the results, water increases the electrophilicity of the dyes and weakens the dye/TiO2 coupling, prohibiting the electron injection toward TiO2. A longer path for charge transfer and a less electron-hole overlap for dihydroxychromens elevate the electron transfer more efficient than trihydroxychromen-based flavonoids. However, the presence of water molecules within an increment in the -OH groups in the flavonoid structures improves their spectroscopic properties, which is related to decrement in the gap of the frontier molecular orbitals and increment in the oscillator strength. Also, such favorable structural effects and influence of the water medium on the polarizability and excited-state lifetime have emerged. According to the energy conversion efficiency, water is a favorable solvent for dihydroxychromen‏-based flavonoids.‏ Finally, different analyses on the structural geometries, excited-state, lifetime within the kinetics and dynamics of the photovoltaic processes were performed and discussed.

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