The Improved Performance Of TiO₂ Nanotube Array Based Dye Sensitized Solar Cells With Barrier Modification

This research is based on the modification treatments of one-dimensional TiO₂ nanotube?TNT?arrays for improving the performance of dye-sensitized cells?DSSCs?.Firstly,the photoanodes had been modified with introducing TiO₂ nanoparticles into TiO₂ nanotube arrays,and then were to be further decorated by different barrier materials' modification.Moreover,we try our best to explain the enhanced performance of modified TiO₂ nanotube arrays-based DSSCs by taking these respects into considerations as follows:enhancement of specific surface area,improvement of light harvesting efficiency,properties of transporting electron or transferring charge,reducing the loss of electron-hole recombination etc.Currently,the TiO₂ nanotube arrays have been widely prepared by two-step anodic oxidation method,which can easily change the length and diameter of TNT by controlling concentration of reaction solution or oxidation time.These highly ordered Ti02 nanotube arrays can provide access to transporting electrons fastly.However,the shortage in specific surface area has detrimentally limited the further development of TiO₂ nanotube arrays based DSSCs.In our previous research work,the TiO₂ nanotube arrays photoanodes have been successfully modified with introducing TiO₂ nanoparticles by two different methods,which can be named TiCl4 bathing treatment and TiO₂ colloidal treatment.After these different treatments,the performance of TNT arrays-based DSSCs had been more excellent because of the improved specific surface area of TNT arrays.However,these introducing TiO₂ nanoparticles could also add some different grain boundaries into TiO₂ nanotube arrays.These grain boundaries would easily become the center of defect recombination,which can help increase the recombination rate of electron-hole pair in DSSCs.To overcome this deficiency and the further improving perpormance of TNT arrays based DSSCs,some semiconductors and insulator whose band are matched with TiO₂ would be chosen as buffer layer and introduced into DSSCs.The role of these buffer treatments can not only avoid the direct contact between TiO₂ photoanodes and a liquid electrolyte,resulting in reducing electron recombination interface,but also form a barrier to decrease the loss of electron combination,and then maximize the performance of the photovoltaic cell device.The main idears of this study can be described as follws:?1?Two different methods,named traditional TiCl4 bathing treatment and TiO₂ colloidal treatment,had been respectively used to modifying the surface of TiO₂ nanotube arrays photoanodes.It has been proved that the grain size of TiO₂ has a great infect on the power conversion efficiency of DSSCs.And also,the 20nm in diameter of TiO₂ nanoparticles has been considered the best choice for improving the performance of DSSCs.On the other hand,the production of TiO₂ colloidal treatment had shown that the diameter of introduced nanoparticles could be albout 20nm.the final experiment result had proved that the performance of TNT arrays based DSSCs after TiO₂ colloidal treatment could be better than that after traditional TiCl4 treatment.?2?Some TiO₂ nanoparticles?about several nanometers in diameter?had been successfully introduced upon on the surface of TiO₂ nanotube arrays by traditional TiCl4 bathing treatment.Furthermore,the HfO₂ nanoparticles ultra-films as buffer layers could be prepared on these TiO₂ nanoparticles.As results,the PCE of 8.657%was obtained in assembled DSSCs.?3?Firstly,TiO₂ nanoparticles made of 20nm in pure particle size were prepared by sol-gel method in our perilous work.Then,an ultrathin film of TiO₂ nanoparticles Hydrolyzed from titanium tetrachloride via sol-gel method is formed on the TiO₂ nanotubes.Sequentially,the HfO₂ blocking layer from the alcoholysis of HfCl4 is deposited on the TiO₂ nanoparticles to turn into the core-shell structure with the former TiO₂ nanoparticles film.In this case,addition of this core-shell structure provided solar cells devices with the PCE of 10.44%.The beneficial effects observed can be ascribed to a combination of three factors:1)improved the electronic properties by the TiCl4 treatment due to the enhancement of Dye adsorption area,2)the tunneling effect of the wide-gap semiconductor HfO₂ buffer layer to reduce the combination of the transport electrons through mesoscopic TiO₂ layer,and 3)a high specific dye loading that becomes possible for HfO₂ modified the TiO₂ nanotubes.?4?And also,the multilayer structure:NiO/TiO₂ double layers/TiO₂ nanotube arrays for improving PCE of DSSCs have been being in research.These TiO₂ nanotube arrays electrodes are coated with TiO₂/NiO baitlayer structure by simple wet chemistry method for dye sensitized solar cells.And also,the structural,electrochemical and optical properties of the TiO₂/NiO core-shell nanocomposites have been investigated.The final experiment results indicate this structure can have an excellent advantage of photoelectric performance.With the optimized experiment conditions,this surprising architecture could help the TiO₂ nanotube arrays based DSSC increase the conversion efficiency to 9.77%.it have been proved that the NiO/TiO₂ multilayer core-shell structure is beneficial to improvement of TiO₂ nanotube arrays-based DSSCs,which is still being in research.The TiO₂ nanotube arrays photoanode of TiO₂ large nanoparticle/TiO₂ nanoparticle/TiO₂ nantube composite structure was also investigated,and some research achievements had been made.The infuence of blocking layer on the suppressing of charge recombination of the photoanodes had been studied in this project as well and accordingly to understand the role of the blocking layer on the photovoltaic properties and charge transport of the hierarchical core-shell nanoarray photoanodes.The internal charge transport mechanisms and models of TiO₂ nanoarrays will be proposed in this project and this is possible to improve the photovoltaic performance of DSSCs dramatically.This topic is significantly important for the exploring of high conversion efficiency,low-cost DSSCs and understanding their internal charge transport mechanisms perfectly.