How to Optimize the Interface between Photosensitizers and TiO2 Nanocrystals with Molecular Engineering to Enhance Performances of Dye-Sensitized Solar Cells?
In this work, the interfacial properties of a series of metal-free organic naphthodithienothiophene (NDTT)-based photosensitizers adsorbed on TiO2 surfaces were investigated by a combination of ab initio calculations and experimental measurements. The calculations and experiments reveal that because of the efficient charge transfer from the adsorbed dyes to TiO2 nanocrystal surface there is an upward shift for the energy levels of dyes and a downward shift for the conduction band of surface TiO2 and that the band gaps for both of them are also reduced. Such electronic level alignments at the interface would lead to increased light absorption range by adsorbed dyes and increased driving force for charge injection but reduced open-circuit potential (V(oc)). More interestingly, we found that molecule engineering of the donor group and introducing additional electron-withdrawing unit have little effect on the electronic level alignments at the interface (because band gaps of the dyes adsorbed on TiO2 surfaces become approximately identical when compared with those of the dyes measured in solution) but that they can affect the steric effect and the charge separation at the interface to tune V(oc) and the short-circuit current density (J(sc)) effectively. All these findings suggest that optimizing the interfacial properties of dyes adsorbed on TiO2 surfaces by synchronously modifying steric effects of dye molecules anchored on TiO2 and charge-transfer and separation properties at the interfaces is important to construct efficient dye-sensitized solar cells.
School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, PR China.
Jiaxin
J
Zheng
Department of Chemistry and Institute of Molecular Functional Materials, Hong Kong Baptist University , Kowloon Tong, Hong Kong SAR, PR China.
Kai
K
Zhang
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, PR China.
Yanyan
Y
Fang
School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, PR China.
Yunxing
Y
Zuo
School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, PR China.
Yandong
Y
Duan
School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, PR China.|Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
Zengqing
Z
Zhuo
Department of Chemistry and Institute of Molecular Functional Materials, Hong Kong Baptist University , Kowloon Tong, Hong Kong SAR, PR China.
Xuanming
X
Chen
Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
Wanli
W
Yang
School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, PR China.|Beijing National Laboratory for Molecular Sciences, Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, PR China.
Yuan
Y
Lin
Department of Chemistry and Institute of Molecular Functional Materials, Hong Kong Baptist University , Kowloon Tong, Hong Kong SAR, PR China.
Man Shing
MS
Wong
School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, PR China.
Feng
F
Pan
DSSCs; ab initio calculations; electronic structure; interface; metal-free photosensitizer; steric effect