Simulation Of Cold Rolling Process Of Flexible Stainless Steel And Preparation Of TiO₂Nanotube Arrays On The Stainless Steel Substrate

Stainless steel （SS） substrate for flexible solar cell was a kind of precise sheet with thin thickness.It often contained some shape defects for the limit of the rolling facility and rolling process duringfabrication and could hardly meet the requiments for a solar cell. Thus, considering the preparationand utilization request for a solar cell based stainless steel substrate, the rolling process of suchstainless steel substrate should be optimized. At first, the multi-rolling process of the stainless steelsubstrate for a dye-sensitized solar cell （DSSC） was simulated by finite element method （FEM）. Onthe basis of the reliability of the FEM model, verified by the comparison between the simulationresults and the actual ones, the influence of rolling reduction and tension on the rolling force andshape of the substrate was investigated respectively. The results indicated that the increment in rollingreduction not only led to the raise of rolling force, but also enlarged the edge-drop rate, crown andworse the smoothness of the strip. Moreover, at the time when both of front and back tensionincreased, the rolling force decreased and edge-drop rate enhanced. It was concluded that using thesimilar back/front tensile force method of higher back than front under the reduction of20%couldassure the rolling mills’ safety and the smoothness of the strip.Secondly, highly ordered titanina nanotube arrays （NTAs） were fast fabricated on stainless steelsubstrate by anodization from the pure Ti film deposited by direct current （DC） magnetron sputtering.By observing the current transient recorded during anodization under60V in the ethylene glycol （EG）based electrolyte, in the presence of0.5wt.%NH4F and3vol.%H2O, the mechanism of TiO₂nanotubeswith high growth rate was analyzed. Besides, the TiO₂NTAs were characterized by means offield-emission scanning electronic microscope （FESEM）, X-ray diffraction （XRD） andelectronchemical station （CHI） respectively. It was found out that on the smooth SS substrate, thegrowth rate of the NTAs was up to20.7nm·s-1. After5min anodic oxidation, TiO₂NTAs with thelength of6.2μm, tube diameter and tube thickness of50nm were well contacted with the substrate anda sandwich structure of porous TiO₂NTAs/Ti/SS substrate was formed at last. After the NTAs beingannealed at450℃, the structure of the NTAs converted to anatase and the NTAs performed a betterphotoelectronchemical property than the nanopartical （NP） films.In order to enhance the adhesion between nanofilms and substrate, stainless steel withsandblasting surface was chosen as the substrate. When the Ti film on the SS sheet with sandblastingsurface was anodized for12min, the length of TiO₂NTAs reached7.07μm and a good adhesion of theII TiO₂NTAs to the substrate was still performed. The anodic transient and FESEM results showed thatfull morphology of the sandblasting surface was benefit for the formation of Ti film with densecolumnar microstructure, which led to a more stable-going growth of TiO₂NTAs afterwards.Finally, DSSCs with the photoanode of smooth SS substrate/Ti film/TiO₂NTAs and sandblastingSS substrate/Ti film/TiO₂NTAs were assembled and the J-V properties before and after bending werecharacterized. It was concluded that for a sandblasting based DSSC the bending times hardly affectedthe open-circuit photovoltage （Voc） and fill factor （FF） and also had less effect on the short-circuitphotocurrent density （Jsc） and conversion efficiency （η） in comparison with the smooth substrate one.In a word, using the sandblasting surface SS sheet as the substrate was good for the stability of thephotoanode consist of TiO₂NTAs.