Promising architectures modifying the D-π-A architecture of 2,3-dipentyldithieno[3,2-f:2′,3′-h]quinoxaline-based dye as efficient sensitizers in dye-sensitized solar cells: A DFT study

As reported, (E)-2-cyano-3-(2,3-dipentyl-9-(7-(4-(p-tolyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indol-7-yl) benzo[c] (Cui and et al., 2019; He and et al., 2017; Feng and et al., 2013) [1,2,5]thiadiazol-4-yl)-5,6-dihydrodithieno[3,2-f:2',3'-h]quinoxalin-6-yl)acrylic acid (DQ5) with D-A-pi-A architecture was successfully synthesized, its electrochemical and photophysical properties were determined. It has a rigid dipentyldithieno[3,2f:2',3'-h]quinoxaline (DPQ) unit. DQ5, as a DPQ-based organic dye-sensitized solar cell, obtained an excellent power conversion efficiency of 7.12%. Based on this result, and in addition to DQ5, and to establish structure-property relationships, the electrochemical and photophysical properties, intramolecular charge transfer indices, reorganization energies, exciton binding energies and transition density matrix graphs in chloroform solvent of six new architectures derived from DQ5 were calculated using the DFT/and TDDFT/CPCM/ BHandHLYP/6-31 thorn G(d,p). The new architectures included D-A-A-pi-A (D1), D-A-D-pi-A (D2), D-D-A-pi-A (D3), DD-D-pi-A (D4), D-D-pi-A (D5), and D-pi-A (D6). The calculated results indicate that different architectures can modify the energy levels of HOMO and LUMO and ease intramolecular charge transfer and increase charge injection at the interface of dye/TiO2. The binding energies, electronic, and optical properties of the sensitizers@TiO2 cluster have also been explored. The light was shed on the electron/hole injection barrier and bandgap alignment as well. The sensitizers containing the D and/or A moiety, e.g., benzothiadiazole and/or benzo[c]thiophen showed larger binding energies than its absence in derivative, e.g., D6. Comprehensible intramolecular charge transfer was found in sensitizers before and after adsorption @TiO2 cluster in studied compounds. Different architectures derived from DQ5 can provide a new strategy to provide novel DPQ-based dyes and focus on the preparation of dyes with better performance.