Theoretical design of new carbazole based organic dyes for DSSCs applications. A DFT/TD-DFT insight

New series of organic dyes M-i (i = 2-10) derived from M-1 have been investigated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods, to find out the effect of different internal acceptor groups on their efficiency in DSSCs. The geometries, electronic structures, absorption spectra, dipole moments, and molecular electrostatic potential of these isolated dyes and dye-(TiO2)(6) systems were investigated and discussed. Besides, some quantify parameters influencing the power conversion efficiency (PCE) such as light-harvesting efficiency (LHE), electron injection driving force (delta G(inject)) and regeneration driving force (delta G(reg)) were also calculated to examine the most appropriate organic dyes for DSSC applications. Theoretical results indicated that all designed dyes exhibit a significant decrease in the gap energy with increasing dipole moments, and red-shifted absorption spectra (except that M-2 is blue shifted) compared to M-1 (reference dye), which revealed that these designed dyes are promising candidates for DSSC applications. Accordingly, the introduction of new internal acceptor group in D-A-pi-A structure may be the best strategy for improving the photovoltaic performances.