Preparation Of Low Temperature TiO₂ And Its Application In Perovskite Solar Cells

In recent years,organic-inorganic hybrid perovskite material CH₃NH₃PbX₃（X = Cl,Br,I）,due to low exciton binding energy,suitable band gap,long carrier diffusion length,high light absorption coefficient and solution processing Performance,has aroused people’s attention.Based on this hybrid perovskite material,the efficiency of photovoltaic devices has exceeded 22.1%.It can reach the level of crystalline silicon solar cells and can be seen as a candidate for the next generation of photovoltaic devices.However,as the electron transport layer in a perovskite solar cell device,traditional TiO₂ processing method requires rather high annealing temperature（>500 ?C）,thus hindering its application to flexible wearable devices.Therefore,finding a low temperature TiO₂ preparation method and without the loss of efficiency,we can prepare low-temperature perovskite solar cell.We found that the TiCl₄ directly generated rutile TiO₂ by hydrolysis at 70℃,which not only can be obtained at low temperature,but also can directly achieve the chemical bath film,eliminating the need for spin coating process.We optimized the hydrolysis concentration and time of Ti Cl4,and finally prepared a high quality Ti O2 film which could be applied to Perovskite solar cells.1.Typically,a compact layer of rutile TiO₂ is deposited onto fluorine-doped tin oxide（FTO）coated substrates,in an aqueous Ti Cl4 solution at 70℃.By controlling the concentration of Ti Cl4 and the growth time,we can use 200 mM TiCl₄ aqueous solution for 60 min to obtain rutile TiO₂ film with a film thickness of about 60 nm.The photoelectric conversion efficiency was 11.18% by using FTO / TiO₂ / CH₃NH₃PbI₃ / spiro-OMeTAD / Au structure.2.UV ozone treatment can not only remove the organic residue on the surface of the oxide,but also increase the surface wettability of TiO₂.Through the surface treatment of TiO₂,we can increase the efficiency of perovskite solar cells to 12.62%.The mechanism was analyzed by absorption spectroscopy,PL,electrochemical impedance,SEM,IV,IPCE and so on.3.The niobium element doping can enhance the carrier concentration of TiO₂ and enhance its electron transport performance.This method not only improve the efficiency of the devices to 16.12%,but also reduce the hysteresis effect.Through the XPS,electrochemical impedance,PL and other means to explain the principle.Using the same method,the other elements of TiO₂ doped（tantalum,tungsten,etc.）,the performance of perovskite solar cells also can be improved.4.The printing of large area perovskite film was realized by using TiO₂ film prepared by low temperature as substrate and inkjet printer（DMP-2831）.Through the adjustment of the solvent,we can achieve the efficiency of 15.27% in perovskite solar cells,higher than the reference spin-coating device efficiency of 12.69%.By inserting 5nm C₆₀ into TiO₂ and CH₃NH₃PbI₃ thin films,the interface performance can be further improved,and finally the efficiency of 17.04% is obtained.In this paper,high quality TiO₂ thin films were prepared by low temperature chemical bath method,which was applied to perovskite solar cells,and the efficiency of the devices was improved by UV irradiation.In order to further optimize the device performance,TiO₂ has been doped with different elements,making the device efficiency exceeded 16%.In order to replace the spin coating,to achieve a large area perovskite solar cell,we use one-step inkjet method to prepare perovskite devices.The performance is better than the spin coating method,for future inkjet printing large area perovskite solar cells to lay a solid foundation.At the same time,the C₆₀ interfacial modification between TiO₂ and CH₃NH₃PbI₃ thin film was carried out,and the efficiency of the perovskite solar cell was finally exceeded by 17%.