Quantum Mechanical Investigation of Carbazole-Coumarine Hybrid Interactions with TiO2 in organic Dye-Sensitized Solar Cell

Abstract

Due to the flexibility, limpidity, and high proficiency compared to conventional inorganic solar cells, dye-sensitized solar cells (DSSCs) have received much attention in past years. DSSCs are serene of mostly non-toxic constituents and might be made up without exclusive and energy-intensive high temperature and high vacuum procedures. In this thesis, we have investigated the heterogeneous adsorption mechanism of five novel dyes of coumarins namely 6, 8-Dimethoxy-7-methyl-3-phenylisocoumarin, 6, 8-Dimethoxy-7-methyl-3-(p-tolyl) isocoumarin, 6, 8-Dimethoxy-7-methyl-3-(4’-methoxyphenyl) isocoumarin, 6, 8-Dimethoxy-7-methyl-3-(4’-chlorophenyl) isocoumarin, 6, 8-Dimethoxy-7-methyl-3-(4’-nitrophenyl) isocoumarin, and a single carbazole namely, 3,5-dinitro-N-octylcarbazole with titanium dioxide (TiO2) to determine the adsorption prosperity based on computational studies. Based on quantum chemical findings calculated adsorption energy was found more favorable for 6, 8-Dimethoxy-7-methyl-3-(4’-chlorophenyl) isocoumarin as compared to the other four isocoumarin dyes due to the presence of the Cl group possessing electron-donating capability and having a more negative value of adsorption energy i.e., -7.128 ˣ 103eV. On the other hand, a heterogeneous adsorption mechanism was also considered for five hybrids of isocoumarin and a carbazole dye (HK-1), (HK-2), (HK-3), (HK-4), (HK-5), to determine the electron transfer and injection phenomenon based on computational studies. Among all five hybrid dyes (HK-3) showed the greatest efficiency of electron injection from ELUMO of the hybrid into the conduction band of nanocrystalline TiO2 in DSSC. The results revealed that hybrids show high efficiency to inject the electron into the conduction band of TiO2 leading to oxidation of dye-hybrids and transfer and diffusion of the electron to counter electrode. Results demonstrated that electron injection efficiency increased in the presence of dye-hybrids as a photosensitizer.