Seed-mediated Growth Of High Conductive And Transparent Anatase Nb-TiO₂ Films

Transparent conducting oxide films?TCOs?such as indium tin oxide?ITO?are widely used in photovoltaic and photonic devices.However,owing to the small natural abundance of indium and its toxicity,high-purity anatase Nb-TiO2?NTO?is proposed as an alternative but materials fabrication is quite difficult.Costly substrates with a specific orientation such as sapphire must be used to avoid formation of the rutile phase and to obtain transparent and conductive NTO films,so scaling up is difficult thus hampering commercialization.Herein,in order to control the crystal orientation of TiO₂,two-step preparation is described.NTO films with anatese seeds are first prepared on economical soda-lime glass substrate by DC magnetron sputtering and then annealed in Ar with 5 at.%H₂ at 400?.Owing to the smaller nucleation free energy of anatase than rutile when the grain size is smaller than 14 nm,nano-scale anatase seeds nucleate preferentially by precise energy control of the deposition particles during magnetron sputtering.The mechanism of the seed-mediated growth NTO is studied by in situ heating transmission electron microscopy?TEM?comparing with amorphous NTO and multi-phase NTO.Besides,the structure,chemical composition,and optoelectrical properties of the NTO films are studied,provding that NTO films with pure anatase phase crystallized by seed-mediated growth method exhibit best conductivity and transmittance.In order to meet the needs of some specific applications such as CIGS and CdTe thin-film solar cells,high conductive and transparent NTO with thicker films are prepared by seed-mediated method in this work,and the morphology,structure,optoelectrical properties and relationship with film thickness are also studied.The experiment result show that the resistivity decreases to 8.1×10^-4??cm for a thickness of 320 nm,and the average transmittance in the visible region increases monotonically to 73%as the thickness is reduced from 400 nm to 280 nm.For further improving the transmittance and broadening its apply field,we use the glass substrates coated with optimal antireflection layers in both sides,and simulate the application of NTO films in CdS/CdTe thin-film solar cells by Essential Macleod 8.0simulation,optimizing the thickness of CdS and NTO layers.The high transparency of 84.91%in visible region suggest potential application in CIGS and CdTe thin-film solar cells.