有机染料D-SS和D-ST用于染料敏化太阳能电池光敏剂的比较

为了揭示D-SS和D-ST分子敏化的染料敏化太阳能电池(DSSCs)的物理机制,采用密度泛函理论(DFT)、含时密度泛函理论(TDDFT)和自然键轨道(NBO)分析,模拟计算染料D-SS和D-ST分子的结构、紫外-可见吸收光谱和能级结构.D-SS的紫外-可见吸收光谱相比于D-ST的有明显的红移,而且D-SS分子的摩尔吸光系数也高于D-ST分子的.D-SS分子本应该比D-ST分子拥有更高的俘获太阳辐射光子的能力,但由于D-SS分子的最高占据分子轨道(HOMO)能级位置比氧化还原电解质(|-/|-3)的氧化还原能级高,处于光激发态的D-SS分子向TiO2电极注入电子而被氧化后,不能顺利地从电解质中得到电子而还原,使得D-SS分子俘获光子的能力不能充分发挥,从而严重地降低了由其敏化的DSSCs的光电性能和光电能量转换效率.揭示了D-SS敏化的DSSCs的光电性能,特别是光电能量转换效率比D-ST敏化的DSSCs的低的原因.染料敏化剂分子的HOMO能级的位置对于DSSCs来说也是很重要的,用于DSSCs的有机敏化剂分子的HOMO能级的位置必须低于氧化还原电解质的氧化还原能级.

Comparison of D-SS and D-ST Dyes as Photo Sensitizers in Dye-Sensitized Solar Cells

The molecular structures,UV-Vis absorption spectra,and energy level structures of the dyes D-SS and D-ST were simulated using density functional theory,time-dependent density functional theory (TDDFT),and natural bond orbital analysis,which provided the physical mechanisms of dye-sensitized solar cells (DSSCs) containing D-ST and D-SS.The UV-Vis absorption spectrum of D-SS showed a significant red shift compared with that of D-ST and the molar absorption coefficient of D-SS was higher than that of D-ST.D-SS molecules should have a higher solar radiation photon-harvesting ability than D-ST molecules,but the energy level of the highest occupied molecular orbital (HOMO) of D-SS was higher than the redox energy level of the electrolyte (I-/I-3).As a result,an optically excited D-SS molecule cannot be successfully recovered by accepting an electron from the electrolyte after being oxidized by injecting an electron towards the TiO2 electrode.This limits the photon harvesting ability of D-SS molecules,and thereby significantly decreases the photovoltaic properties and energy conversion efficiency of DSSCs containing D-SS.This allows the photovoltaic properties of DSSCs containing D-SS to be understood,especially why its photovoltaic energy conversion efficiency is lower than that of DSSCs containing D-ST.The position of the HOMO energy level of dye-sensitized molecules is very important for the operation of DSSCs,and that of the organic sensitizer molecules used in DSSCs must be lower than the redox energy level of the electrolyte.