Preparation And Properties Of Electrochromic Devices Based On Niobium Pentoxide Thin Films

Electrochromicsmart windows have broad application prospects in the fields of building energy conservation,rearview mirrors,displays,etc.Due to their advantages of low energy consumption,intelligent control,and reversible color changes.Nb₂O₅ is a kind of inorganic electrochromic material with great potential.At present,its preparation method is relatively complicated,and its electrochromic performance cannot reach the level of practical application.In this thesis,electrochromic Nb₂O₅ thin films are prepared by simple,safe and environmentally friendly sol-gel method and solvothermal method,and the prepared Nb₂O₅ thin films are used to assemble electrochromic devices.The effects of solvent,temperature and other process conditions on film morphology and electrochromic performance,as well as the electrochromic device performance are mainly studied.The research content is as follows:(1)Using niobium ethoxide as the niobium source,By combination of sol-gel method and spin coating technology,Nb₂O₅ films were prepared on FTO conductive glass and assembled into electrochromic devices.The effect of annealing temperature on the morphologies and electrochromic properties of Nb₂O₅ films was mainly studied.The results show that when the annealing temperature is lower than 400?,Nb₂O₅ is amorphous,when the annealing temperature is higher than 500?,Nb₂O₅ is orthorhombic crystal.When the heat treatment temperature is 600?,the electrochromic performance of the Nb₂O₅ film is the best,its optical modulation amplitude is 38.6%at a wavelength of 800 nm,the coloring time is 40.6 s,the bleaching time is 38.7 s,and the coloration efficiency is 73.3 cm²·C^-1.The optical modulation of the electrochromic device is 24.6%at a wavelength of 710 nm,the coloring time is 22.3s,and the bleaching time is 3.5 s.(2)Using niobium oxalate as the source of niobium.Nb₂O₅ film was grown on FTO conductive glass by solvothermal method and assembled into electrochromic device.The effects of solvothermal reaction time,reaction temperature,and ethanol concentration in the precursor solution on the morphologies and electrochromic properties of Nb₂O₅ films were studied respectively.The effect of electrolyte type on the performance of electrochromic devices is also studied.The results show that when the reaction temperature is 180?and the reaction time is 2 h,the XRD diffraction peak intensity of Nb₂O₅ is stronger;when the concentration of ethanol in the current driver solution is 30%,the Nb₂O₅ film has a porous network structure and exhibits Good electrochromic performance:the optical modulation is 69.0%at a wavelength of 800nm,the coloration time is 10.6 s,the fading time is 0.7 s,the coloration efficiency is85.9 cm²·C^-1,and the cycle stability is at least 500 times.When the electrolyte solution is Li TFSI(PC),the performance of the electrochromic device is the best:the optical modulation is 52.2%at a wavelength of 800 nm,the coloration time is 41.1 s,the bleaching time is 10.3 s,and the colored efficiency is 172.2 cm²·C^-1.(3)A complementary device consisting of Nb₂O₅ film(as the electrochromic layer)and Ni O film(as the ion storage layer)is fabricated,and its electrochromic performance is studied.In comparison with the aforementioned single Nb₂O₅ device,the coloring speed,bleaching speed and the coloration efficiency of the Nb₂O₅/Ni O complementary are increased by 69%,29%and 55.9%,respectively,while a large optical modulation of 52%is also achieved.The improvement of the electrochromic performances of complementary devices is due to the prepared Ni O film has a porous surface structure,which can store more Li⁺.Under the driving of an external voltage,Li⁺could be quickly embedded and released from the Ni O film,thereby the electrochromic performance of the device is improved.