| AZO thin films prepared on flexible substrates have wide application prospect in the fields of flexible display, flexible solar cell etc., being presently hot topic noticed by researchers. However, AZO films on flexible substrates exhibit poor crystalline quality, and are easy to crack due to soft texture and no enduring high temperature of flexible substrates,which seriously influences the conductive properties in AZO films. Moreover, the carrier concentration in AZO films with good conductivity is much higher, leading to dramatic decrease of the transmittance in near-infrared region. Focusing in the above problems, we significantly improved the conductive properties in AZO films prepared by magnetron sputtering, via exploring optimal sputtering power, using multiple film-forming process,introducing H2 to sputtering environment and adding buffer layer etc. Taking HAZO films on PET substrate as an example, we also investigated some properties directly related to practical applications including adhesion, thermal stability and transmittance in near-infrared region. Finally, we prepared HAZO films on flexible substrates with the optoelectronic properties achieving practical application standards.By considering significant influence of sputtering power on the resistivity in AZO films,and the warping and deformation of flexible substrates resulting from high power, the sputtering power was first explored. It shows that the minimum resistivity can be obtained at70 and 80 W in AZO films on PET and PMMA, respectively. And the corresponding values are 4.19×10-3 Ω·cm、2.08×10-3 Ω·cm. Since the above resistivity is still much higher, and XRD results exhibits that the best crystalline quality was respectively achieved on two subatrates at 80 and 90 W where flexible substrates had been heated to warp and deform with cracked surfaces, poor conductivity and low transmittance, AZO films were prepared on PET and PMMA substrates by using multiple film-forming process. When AZO films were prepared at 80 and 90 W by four deposition process with 5 min break time for each time, the deposited films show good crystalline quality, no cracking and less acceptors such as VZn and Oi. The resistiyity of 2.47×10-3 Ω·cm and 9.50×10-4 Ω·cm were obtained on PET and PMMA,respectively. The transmittance in visible light region will be influenced by film cracking, for example, for AZO films deposited on PET at 80 W, the average transmittance inreases from80.53% for the film deposited by single depositon process to 87.13% for the film deposited by five deposition process.To further reduce the resistivity in AZO films on flexible substrates, HAZO films were prepared by introducing H2 to sputtering atmosphere and using multiple film-forming process.The resistivity decreases with the increase of H2 ratio, the minimum resistivity of 8.03×10-4Ω·cm and 7.56×10-4 Ω·cm was respectively achieved on PET and PMMA when the H2 ratio is4%. We suggest that H can passivate the acceptor-like defects such as VZn, Oi, adsorbed oxygen species, surface dangling bonds etc, by forming VZn-Hn complexes, the desorption of surface oxygen species and the out-diffusion of Oi etc., the compensating and scattering effects to donor electrons will be weakened, which induces the improvement of conductive properties in the films. AZO buffer layer with high resistance was also added to improve the films’ crystalline quality and restrain the diffusion of moisture and gas from flexible substrates to the films, the resistivity in HAZO films on PET and PMMA can decrease to6.93×10-4 Ω·cm and 6.48×10-4 Ω·cm. The introduction of H2 has little influence on the transmittance, however, after the addition of buffer layer the transmittance will decrease.Finally, the adhesion and thermal stability properties between HAZO films and PET substrates have been measured, and the results show that they are close to the values obtained from the commercial ITO/PET films, basically reach the applicable standard. The above HAZO films were fabricated by using ZnO target with 2 wt.% Al2O3, the carrier concentration is too high(1021 cm-3), which leads to their low transmittance in the near-infrared region. Therefore, the ZnO target with 1 wt.% Al2O3 was selected to prepare HAZO films, and following results were obtained. Under the condition of keeping the resistivity at the order of 10-4 Ω·cm, the carrier concentration decreases from 2.12×1021 /cm3 to 8.32×1020 /cm3 and the carrier mobility increases from 5.56 cm2 /V·s to 7.28 cm2 /V·s,consequently the transmittance in near-infrared region is improved. |
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