激光辐照对热退火金属/掺氟二氧化锡透明导电薄膜光电性能的影响

Effects of laser irradiation on the photoelectric properties of thermal-annealed metal/fluorine-doped tin oxide transparent conductive films

采用532 nm纳秒脉冲激光对热退火的铝(Al)/掺氟二氧化锡(FTO)、铜(Cu)/FTO和银(Ag)/FTO三种双层复合薄膜表面分别进行处理,结果显示薄膜样品的光电性能都得到提高.其中,热退火Ag/FTO薄膜的平均透光率(400—800 nm)增幅最大,从72.6%提高到80.5%,主要是由于其表面产生了具有减反增透作用的光栅结构.激光辐照后热退火Ag/FTO薄膜的导电性也略有提高,其方块电阻从5.6Ω/sq下降到5.3Ω/sq,原因主要是激光辐照的热效应造成的退火作用使薄膜的晶粒尺寸增大,减少了晶界散射而使载流子迁移率提高.计算结果显示,激光辐照后热退火Ag/FTO薄膜的品质因子从0.73×10-2Ω-1增大为2.16×10-2Ω-1,表明其综合光电性能得到显著提高.激光辐照可同步实现薄膜表面光栅结构的制备和附加退火作用,这为金属层复合透明导电薄膜光电性能的综合优化提供了新的思路.

Three kinds of bilayer films, i.e. aluminum（Al）/fluorine-doped tin oxide（FTO）, copper（Cu）/FTO and silver（Ag）/FTO, are prepared by coating a commercial FTO glass with sputtered metal layers, and subsequently thermally annealed. Then all the as-annealed bilayer films are irradiated using a 532 nm nanosecond pulsed laser. X-ray diffraction（XRD） analysis confirms that all the laser-irradiated films have underwent laser annealing, resulting in an improvement in their photoelectric properties. More significantly, after laser irradiation, the as-annealed Ag/FTO film exhibits the highest increment in average transmittance（400—800 nm） that is increased from 72.6% to 80.5%. This should be attributed mainly to the formation of laser-induced grating structures that have anti-reflection effect on their surfaces.It is also found that the laser irradiation decreases the sheet resistance of the as-annealed Ag/FTO film from 5.6 to 5.3Ω/sq. The annealing caused by thermal effect of laser irradiation gives rise to an increase in grain size, thereafter reduces carrier scattering at grain boundaries and enhances carrier mobility, which should be responsible for the improvement in conductivity. The calculated results show that after laser irradiation the figure of merit of the as-annealed Ag/FTO film is greatly increased from 0.73×10 ^-2to 2.16×10^ -2Ω^-1, indicating a significant enhancement in the overall photoelectric property of the film. Laser irradiation can simultaneously achieve fabrication of grating structures and laser annealing,providing a new idea for performance optimization of metal-layer-composited transparent conductive films.