Shangfeng Xiao

Theoretical modeling of the series resistance effect on dye-sensitized solar cell performance

Based on the continuity equations and the equivalent circuit, the conductivity of substrates and the resistances of silver grid in dye-sensitized solar cell (DSC) are investigated. The complete I-V characteristics of DSC are obtained with different internal resistances. The theoretical and experimental results show internal resistances dominate the fill factor of DSC. At the same time, DSC module is investigated by numerical simulation under parallel connection with different illumination intensities. It can be found the high resistivity of substrates and the high illumination intensity lead to a lower optimal width in the DSC module.

Multiple adsorption of tributyl phosphate molecule at the dyed-TiO2/electrolyte interface to suppress the charge recombination in dye-sensitized solar cell

Electron recombination and dye aggregation at the dyed-TiO2/electrolyte interface are still problems in dye-sensitized solar cell (DSC) research. In this paper, tributyl phosphate (TBpp) as a special additive to modify the dyed-TiO2/electrolyte interface was introduced to enhance the photovoltaic performance. The adsorption mode of TBpp and the interaction between cis-dithiocyanate-N,N′-bis-(4-carboxylate-4-tetrabutylammonium carboxylate-2,2′-bi-pyridine) ruthenium(II) (N719) and TBpp were investigated. It was found that one TBpp parent molecule split into several smaller fragments and formed four anchoring modes on the TiO2 surface. It was very interesting that the molecular cleavage of TBpp and adsorption of N719 assisted each other on the sensitized TiO2 surface. The fragments distributed around N719 result in steric hindrance, consequently hydrogen-bonding among N719 molecules was decreased. The unstable type N719 transformed into stable type N719 accompanied by molecular cleavage of TBpp and the N719 aggregation was reduced. Furthermore, these new fragments were multiply adsorbed on the non-sensitized TiO2 surface to form an insulating barrier layer. Therefore, the electron recombination at the dyed-TiO2/electrolyte interface was restrained. Besides the change of surface configuration, the TiO2 band edge negatively shifted and the rate of electron transport in the TiO2 films decreased with the addition of TBpp. As a result, an increase in the photoelectric conversion efficiency (η) was obtained of almost 40%.

Regulating mesogenic properties of ionic liquid crystals by preparing binary or multi-component systems

In this study, a series of binary systems based ionic liquid crystals (ILCs) C12MIm(BF4)yIx (x + y = 1) are prepared by mixing ILCs 1-dodecyl-3-methylimidazolium iodide (C12MImI) and 1-dodecyl-3-methylimidazolium tetrafluoroborate (C12MImBF4), aiming to combine the properties of both C12MImBF4 and C12MImI. Their mesogenic properties are characterized by thermal analysis, polarized optical microscopy, X-ray diffraction as well as anisotropic ionic conductivity measurements. It is found that the smectic A phase with interdigitated bilayer structure is observed in the C12MIm(BF4)yIx series. The binary system C12MIm(BF4)yIx has a larger mesophase temperature range and interdigitated layer spacing than pure C12MImBF4. And the anisotropic ionic conductivity of the binary system, including parallel and perpendicular to smectic layer, is higher than pure C12MImI. Moreover, in binary system C12MIm(BF4)yIx, with the increasing content of C12MImI the ability of the anion to form three dimensional hydrogen bonds increases, resulting in the increase of the mesophase temperature range, interdigitated layer spacing and the decrease of anisotropic ionic conductivity. Furthermore, multi-component system based ILCs are obtained by introducing iodine to the binary system, and the mesophase temperature range is lowered, which is associated with the weak ability of I3− to form hydrogen bond with cations. All these results suggest that we can regulate the mesogenic properties of ILCs as we need by making binary or even multi-component systems.

The effect of long-term real-time monitoring on interface and photoelectric performance of dye-sensitized cells

In this paper, the effect on DSC photovoltaic performance and its mechanism under long-term real-time monitoring were investigated by Raman spectroscopy and electrochemical impedance spectroscopy. The experimental results indicated that the Raman spectroscopy, interface impedance, electron transport and recombination time change with the same trend after 10000 cycles under -0.1-0.7 V bias and open circuit condition. Real-time monitoring has no effect on cells performance. However, if the bias voltage of real-time monitoring was much higher than open circuit voltage of the DSC, the DSC performance would be affected and dye desorption may occur. A dramatic reduction in the cells performance was observed. The results of real-time monitoring be distorted.