Research On Dye-Sensitizes Solar Cells Based On TiO₂Nanoarray Films

Dye-sensitized solar cells （DSCs） are considered to be a promising alternative toconventional silicon solar cells due to their advantages of high conversion efficiency and lowcost. In a dye-sensitized solar cell, TiO₂nanostructured film electrode is the core componentof the cell since its structure and morphology play an important role on determining thephotocurrent density and even the conversion efficiency of the cell. Compared withnanocrstalline porous films randomLy composed of TiO₂nanoparticles, nanoarray films thatcan provide direct electron transport channels help to improve the collection efficiency ofphotogenerated electrons, thereby increasing the photocurrent density and even thephotoelectric conversion efficiency. Moreover, growth of TiO₂nanoarray films directlyattached on conducting substrates is convenient for fabricating DSCs. However, unlike thatfor ZnO, the symmetry in TiO₂crystal makes it difficult to grow TiO₂one-dimensionalnanoarray. Therefore, researches on the direct growth of TiO₂one-dimensional nanoarrays onsubstrates is not only challenging but also of great significance.In the current work, TiO₂nanoarrays were directly grown on FTO conducting glasssubstrates by the hydrothermal method, which the mixing aqueous solution of tetrabutyltitanate and concentrated HNO₃was used as the growth solution. The crystal structure andmorphology of the obtained TiO₂nanoarrays were characterized by X-ray diffractometer（XRD）, scanning electron microscopy （SEM），transmission electron microscopy （TEM）, andhigh resolution electronic microscopy （HRTEM）. The performance characteristics of theDSCs based on the TiO₂nanoarray films were evaluated by measuring theirphotocurrent-voltage curves. The effects of the amount of concentrated HNO₃and tetrabutyltitanate, reaction temperature and time, and the seed layer on the morphology, thickness, theamount of dye adsorbed of the TiO₂nanoarrays and thus the conversion efficiency of theDSCs based on the nanoarrays were systematically investigated. The suitable conditions forgrowing the TiO₂nanoarrys are obtained. It is shown that the TiO₂nanoarrays prepared by thehydrothermal method are oriented rutile films that are well crystallized, grow perpendicular tothe substrate, and possess a preferential orientation in the [001] direction. The nanarrayobtained from the growth solution containing3mL of tetrabutyl titanate,20mL of concentrated HNO₃,and40mL of deionized water at120℃for9h has a thickness of3.2μm and the DSC based on the nanoarray achieves a photocurrent density （Jsc） of5.86mA/cm2, an open voltage （Voc） of735mV, a fill factor （FF） of53.65%, and an overallconversion efficiency （η） of2.31%.Growth TiO₂nanoarray directly attached on FTO glass substrates by the hydrothermalmethod has the advantages of no need of seed layers, simply process, low temperature, shortreaction time, and no need of replacing fresh growth solution for several times of reaction,which facilitates to mass production.