Study On The Modification Of Photoanode Interfaces For Quantum Dots Sensitized Solar Cells

As the next generation of photovoltaic devices,quantum dots sensitized solar cells（QDSSCs）developed on the basis of dye sensitized solar cells have received much attention due to their theoretical light-to-energy conversion efficiency of 44%.Photoanode is the key component of QDSSCs,and the power conversion efficiency of cells can be effectively increased through optimizing its interface structure.In this paper,the quantum dots and TiO₂ films in photoanodes were designed and modified,and the interfaces of TiO₂ photoanode films were modified by the method of in situ hydrolysis.The influence on the photovoltaic characteristic of cells were investigated.The corresponding mechanisms of improved properties were discussed.The interface of TiO₂ photoanode film in CdS quantum sensitized solar cells was modified by the method of in situ hydrolysis of tetrabutyl titanate（TBT）.The effect of the modification of TBT solution with different concentrations was studied.Results showed that the TiO₂ particles deposited by TBT were anatase phase,and that deposited TiO₂ would passivate the surface defects of the crystalline grains of TiO₂ film.Among all the samples,the sample modified by TBT-2 had the smallest particle size and the strongest photo absorption.Photovoltaic characteristics revealed that the power conversion efficiency of the cell was enhanced significantly for the photoanode interface modified by TBT-2,which increased from 0.90%to 1.88%,compared to a bare CdS quantum dots sensitized solar cell.Meanwhile,the interfaces of TiO₂ photoanode films for CdS/CdSe QDSSCs were modified by in situ hydrolysis of TBT.The effect of TBT modification with different concentrations on the properties of QDSSCs were investigated.Results showed that there were two function mechanisms when TBT modified TiO₂ film.On one hand,deposited TiO₂ occurred heterogeneous nucleation and growth on the interface of TiO₂ porous film,which reduced surface defects of the film.On the other hand,tiny TiO₂ nanocrystals were produced by homogeneous nucleation and subsequent growth,connecting the space between TiO₂ nano-particles of the photoanode film.Similarly,the CdS/CdSe sensitized photoanode modified by TBT-2 showed the strongest light harvesting capability.Photovoltaic characteristics revealed that the power conversion efficiency of the co-sensitized cell was enhanced significantly for the photoanode interface modified by TBT-2,which increased from 3.72%to 4.76%by 28%,compared to a CdS/CdSe sensitized solar cell without modification.Finally,a comparison of conventional TiCl₄ and TBT interface modifications were carried out for the photoanode films of QDSSCs.Results showed that the TiO₂ particles deposited by TiCl₄ were also anatase phase,the same as TBT,and that the porous structure of photoanode films had not been changed with the modification of TiCl₄ and TBT.Compared to the film modified by TiCl₄,the TiO₂ film modified by TBT had a stronger light absorption and larger load amount of quantum dots.The results of photovoltaic characteristics measurement showed that the power conversion efficiency increased by 12%for the sample modified by TiCl₄,which was far less than the sample modified by TBT.