Preparation, Microstructure And Photoelectrical Properties Of Ag-ITO Nanoparticle Composite Films

Ag-ITO nanoparticle composite films with different compositions were prepared on glass substrates by DC magnetron co-sputtering deposition and annealed at different temperatures in air.X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) were employed to investigate the microstructure of the Ag-ITO nanoparticle composite films. According to XRD results, ITO content in the composite films keeps In2O3 crystal structure (bcc), and Ag diffraction signal was undetected. For vol.0.3% Ag-ITO film, with the increase of the annealing temperature from 200 to 400℃, the ITO lattice constant decreases from 11.75 to 11.71 A, and crystalline size increases from 18.1 to 18.6nm. After annealing at 300℃, with the increase of Ag content from vol.0.3% to vol.1.0%, the ITO lattice constant increases from 11.72 to 11.77A, and crystalline size decreases from 18.8 to 16.5nm. SEM results suggest nanoparticles with uniform 30-40nm in size construct the surface of as-deposited Ag-ITO films, which is consistent with the TEM results. AFM results suggest with the increase of the annealing temperature from 200 to 400℃, the average surface particle size of vol.0.3% Ag-ITO film increases from 35.6 to 63.6nm. After annealing at 300℃, when Ag content increases from vol. 0.3% to vol.1.0%, the average surface particle size of Ag-ITO film increases from 54.5 to 90.7nm.According to X-ray photoelectron spectroscopy (XPS) results, the prepared Ag-ITO composite films contain only C, O, In, Sn and Ag elements. Annealing process and introduction of Ag content make In and Sn more fully oxidize into In2O3 and SnO2. In addition, high temperature annealing can promote Ag and/or Ag2O to oxidize into AgO.Obtained with the stylus profiler and the method of fitting film transmittance spectra, the Ag-ITO composite film thickness is about 120-130nm.The optical properties of Ag-ITO composite films with different Ag contents annealed at different temperatures were studied by ultraviolet-visible spectroscopy. As shown by the results, for vol.0.3% Ag-ITO film, with the increase of the annealing temperature from 200 to 400℃, the average transmittance increases from 64.1 to 76.2%, average absorbance decreases from 15.6 to 5.5%, and average reflectance first increases from 20.3 to 26.8 and then decreases to 25.8%. After annealing at 300℃, when Ag content increases from vol.0.3% to vol.1.0%, the film average transmittance decreases from 74.0 to 49.9%, average absorbance increases from 5.2 to 40.2%, and average reflectance decreases from 26.8 to 9.9%.The optical constants of Ag-ITO films were investigated with the method of fitting film transmittance spectra. As suggested by the results, for vol.0.3% Ag-ITO film, with the increase of the annealing temperature from RT to 400℃, the average refractive index first decreases from 3.3 to 2.8 and then increases to 4.8, and average extinction coefficient first decreases from 0.08 to 0.02 and then increases to 0.04.The electrical properties of Ag-ITO nanoparticle composite films were characterized by four-probe technique. The results show for vol.0.3% Ag-ITO film, with annealing temperature increasing from RT to 400℃, the film sheet resistance first decreases from 210 to 34 and then increases to 103Ω/□, which is consistent with the variation of sheet resistance of ITO films with annealing temperature. In addition, the sheet resistance of Ag-ITO composite films is lower than that of ITO films.At last, according to efficiency factor and light splitting ratio, the photoelectrical properties of Ag-ITO nanoparticle composite films were evaluated, and their applicable principles were also elaborated.