Effect of the alkyl chain length on the optoelectronic properties of organic dyes: theoretical approach

摘要

In recent years, investigating organic compounds for Dye Sensitized Solar Cells (DSSCs) applications has received particular attention for its interesting optoelectronics properties. In this article, we have conducted a theoretical study on a series of D-π-A molecules, which have carbazole as a donor (D) and cyanoacrylic acid as acceptor (A) linked by a conjugated bridge. Theoretical calculations were conducted using Density Functional Theory (DFT) and Time-Dependent-DFT to evaluate the substitution effect of linear chains and to elucidate the effects of alkyl chain length (R: H, CH_3 to C_6H_(13)). We have studied the geometrical structures, the electronic and optical properties, the conduction band shift, as well as the charge transfer parameters: IP, EA, PEE, HEP, λ, LHE, V_(oc), ΔG~(inject) and ΔG~(reg) of the studied dyes. According to the results obtained, the substitution of hydrogen H (Dye 1) by the methyl group CH_3 (Dye 2) has, on the one hand, a significant effect on the values of the energies HOMO and LUMO, and on the other hand, the absorption peak is redshifted and the contribution of the electronic transition (H→L) has been improved (664.17 nm and 70%, respectively). However, the substitution of CH_3 (Dye 2) by the other alkyl groups C_nH_(2n+1) (n = 2 to 6) (Dye 3 to Dye 7) has low effects. The best results are obtained by substitution with methyl CH_3, and the increase in chain length, which will require additional computing time, has a low effect on the properties of the dyes studied.