Tailoring of energy levels in (2Z)-2-cyano-2-[2-[(E)-2-[2-[(E)-2-(p-tolyl)vinyl]thieno[3,2-b]thiophen-5-yl]vinyl]pyran-4-ylidene]acetic acid derivatives via conjugate bridge and fluorination of acceptor u
文摘
Density functional theory (DFT) was employed to investigate the role of fused thiophene and bridged thiophene π-linkers as well as acceptor unit fluorination in modifying the properties of dye sensitizers for dye-sensitized solar cells (DSSCs). A series of novel (2Z)-2-cyano-2-[2-[(E)-2-[2-[(E)-2-(p-tolyl)vinyl]thieno[3,2-b]thiophen-5-yl]vinyl]pyran-4-ylidene]acetic acid derivatives were simulated using DFT and time-dependent density functional theory to calculate their electronic and optical properties, population analysis, global reactivity index and light harvesting efficiency. The results showed that dyes with bridged thiophene π-linker have narrower energy bandgap (Eg) and longer absorption wavelength (λmax) than those with fused thiophene π-linker. Also, fluorination of the acceptor unit of the dyes enhanced the electron accepting ability of 2-cyano-2-pyran-4-ylidene-acetic acid by lowering the lowest unoccupied molecular orbital (LUMO) energy, which leads to lower Eg, lower chemical hardness (η), and longer wavelength. Therefore, incorporation of fluorine atoms at the acceptor unit makes the conduction-band potential more favorable, leading to effective charge separation and charge transfer between donor and acceptor.
