染料敏化太阳能电池中染料分子共轭π桥的扩展

以染料分子D5为原型, 采用不同类型和数量的共轭桥单元来设计D-π-A 型有机分子. 采用密度泛函理论(DFT)和含时密度泛函理论(TDDFT)来模拟计算分子的形貌、分子轨道能级以及紫外-可见光谱, 为染料敏化太阳能电池(DSSCs)的敏化分子寻找适合的共轭桥. 采用“次甲基链”、“呋喃环”或“噻吩环”、“次甲基链和呋喃环”或“次甲基链和噻吩环”作为共轭桥单元, 使得分子的吸收光谱依次红移. 随着共轭桥单元的增加, 分子的吸收光谱有剧烈的红移, 但随着共轭桥单元数量的进一步增加, 分子吸收光谱的红移现象减弱. 分子的最低未占据分子轨道(LUMO)能级逐渐降低, 而最高占据分子轨道(HOMO)能级逐渐升高. 采用3个“次甲基链和呋喃环”或者“次甲基链和噻吩环”作为共轭桥时, HOMO能级已经高于氧化还原电解质的能级, 而在极性溶液中, 由2个“次甲基链和噻吩环”单元作为有机分子的共轭桥时, 分子的HOMO能级已经高于氧化还原电解质的能级了. 采用“次甲基链和呋喃环”或“次甲基链和噻吩环”单元作为有机分子的共轭桥时, 吸收光谱有明显的红移,但对于DSSCs的敏化分子, 这样的共轭桥单元只能有1-2个, 不宜过多.

Extension of Conjugate π Bridge in Dye Molecules for Dye-Sensitized Solar Cells

Taking dye D5 molecules as the prototype, different types and different elemental quantities of conjugate π bridge was used to design D-π-A organic molecules. Density functional theory (DFT) and timedependent density functional theory (TDDFT) were adopted to simulate the geometric structures, molecular orbital energy levels, and UV-Vis absorption spectra of the molecules, with the aim of finding conjugate π bridge in the sensitizer molecules for dye-sensitized solar cells (DSSCs). The absorption spectra of the molecules using “methenyl chains”,“furan rings” or “thiophene rings”,“methenyl chains and furan rings”, or “methenyl chains and thiophene rings” as conjugate π bridge showed a gradually increasing red-shifting trend. With increases in the number of conjugate π bridge elements, the absorption spectrum showed an intense red-shift, which weakened gradually; under the same conditions, the lowest unoccupied molecular orbital (LUMO) energy level of the molecules gradually decreased, and the highest occupied molecular orbital (HOMO) energy level gradually increased. The HOMO energy levels of the molecules with three“methenyl chain and furan ring”or“methenyl chain and thiophene ring”elements as conjugate π bridge were higher than the energy level of the redox electrolyte; in polar solutions, the HOMO energy levels of the molecules adopting two “methenyl chain and furan ring” or “methenyl chain and thiophene ring” elements as conjugate π bridge were higher than the energy level of the redox electrolyte. The absorption spectra of the organic sensitizer molecules with several “methenyl chain and furan ring” or “methenyl chain and thiophene ring” elements as conjugate π bridge showed an intense red-shift. These results showed that for DSSCs sensitizer molecules, it is not necessary to have many conjugate π bridge elements; one to two elements is typically enough.