Texture Formation Of TiO₂ Thin Film Deposited By Magnetron Sputtering And Its Effect On Nitrogen Doping

Nowadays,the titanium dioxide(TiO2)has been one of key materials for forming the electron transport layer in organic-inorganic hybrid ammonia lead iodide perovskite solar cells,as its so many excellent features.With the continuous innovation of science and technology,the researchers have prepared the planar heterojunction perovskite solar cells,which use the dense TiO2 film as electron transport layer and hole blocking layer.In this kind of solar cells,the dense TiO2 film plays a significant part,and its performance will directly affect the comprehensive performance.In order to obtain the better performance of dense TiO2 film,and from the viewpoints of improving its carrier mobility and reducing its band gap,the experimental scheme designed in this dissertation could be shown as the follows:(1)TiO2 films are deposited by DC pulse magnetron sputtering technique,which the sputtering power density increases from 0.83-5.00 W/cm2.The dissertation focuses on the effects of substrate temperature and sputtering voltage on the crystalline quality and crystal structure of as-deposited TiO2 films.The results show that with the increase of sputtering power density,the crystal structure of as-deposited TiO2 films gradually change from the amorphous phase structure to anatase phase structure,due to the self-heating factors of the substrate and the increase of sputtering particle energy.Based on the above,the anatase phase TiO2 films are successfully prepared on the polyimide(PI)flexible substrate by the same kind of techniques.(2)The as-deposited TiO2 films prepared in different sputtering power densities are annealed at 600 ? for 1 h.The dissertation focuses on the formation of anatase phase(001)texture(A(001)texture)and its influence on the electron mobility of annealed TiO2 films.The results show that the annealed TiO2 film has A(001)texture,which is deposited with the sputtering power density in 0.83 W/cm2,and the film exhibits a columnar crystal structure.With the increase of sputtering power density,the annealed TiO2 films gradually change from with A(001)texture to without texture,and the columnar crystal structure will also disappeare gradually.In addition,the columnar crystal structure can effectively raise the electron mobility of the TiO2 film.(3)N ion beam implantation technology is adopted to modify TiO2 films to form N-TiO2 films.The dissertation focuses on the chemical bond structure of N element in N-TiO2 films,and its thermal stability.The results show that after N ion beam implantation/diffusion process,the chemical bond structure of N element in N-TiO2 films is dominated by Ti-N and O-N bonds.Among them,Ti-N and O-N bonds doped into TiO2 lattice structure are less,but with better thermal stability.On the contrary,Ti-N and O-N bonds doped into amorphous structure are more,but with poor thermal stability.In addition,N doping technology can also be applied to prepare N-TiO2 films on the PI flexible substrate.(4)A series of annealing/N doping treatments are carried out on the as-deposited TiO2 films,which are deposited with the sputtering power density in 2.50 W/cm2.The dissertation focuses on the effective approach of N doping in TiO2 films.The results show that Ti-N bond doped into TiO2 lattice structure can decrease the band gap of TiO2 films.On the contrary,Ti-N bond doped into the amorphous structure would not.Meanwhile,the annealed TiO2 films are implanted by N ion beam,which can effectively increase the probability of N ion doping into TiO2 lattice structure to form Ti-N bond.Therefore,first crystallization for TiO2 films and then N ion beam implantation,which is the effective approach of N doping.(5)N ion beam implantation process is performed on TiO2 films with different content of A(001)texture.The dissertation focuses on the effect of A(001)texture on N doping efficiency.The results show that with the decrease of A(001)texture in TiO2 film,the ratio of Ti-N bond to O-N bond will monotonically increase.That means A(001)texture in TiO2 film will restrain N ion doping into TiO2 crystal to form the Ti-N bond,which reduces N doping efficiency.For TiO2 electron transport layer,A(001)texture can effectively improve its electron mobility.On the contrary,A(001)texture will also restrain N doping into TiO2 lattice.In the practical applications,it is necessary to balance the positive and negative effects of A(001)texture on TiO2 electron transport layer.