Research On Preparation And Performance Optimization Of Fractal Metal Grid Transparent Electrodes

The metal grid transparent electrode has been known as the best alternative to traditional ITO materials due to its advantages of excellent optical transmittance,good electrical conductivity,high mechanical stability etc.In recent years,the preparation methods have been extensively investigated and continuously optimized,but the study on grid parameters such as grid line width,grid spacing,grid thickness and grid shape which are also important for the photoelectric performance of transparent electrode is relatively few.Moreover,the existing grid parameter optimization method has been limited to improve the comprehensive photoelectric performance of transparent electrodes.At present,the optimization for grid shape（triangle,square,regular hexagon）is the main research on grid pattern,while the research on improving the photoelectric performance of metal grid transparent electrode through the design optimization of grid pattern based on the fractal geometry principle is rarely reported.Based on this,this paper presents the designs for the grid pattern,the effects of grid periods,grid pattern combinations,grid pitches and grid thicknesses on fractal grid mesh transparent electrodes were investigated,and some significant results were finally obtained.1.Nanosecond pulsed laser was used to localized ablate the Ag films（300 nm）deposited on glass substrates by radio frequency（RF）magnetron sputtering.Periodic fractal Ag grid transparent electrodes with periods of 4,9 and 16 were prepared to investigate the influences of the grid periods on the morphology and photoelectric properties of the periodic fractal Ag grid transparent electrodes.Meanwhile,the optimal grid pitch at the optimum grid period was discussed.It was found that the periodic fractal Ag grid transparent electrode could ensure that the optical transmittance was greatly improved without much sacrifice in electrical conductivity compared to the corresponding regular periodic grid transparent electrode,and then the comprehensive photoelectric performance was improved effectively.The experimental results indicated that the periodic fractal Ag grid transparent electrode with period 4 and grid pitch p of 0.7 mm showed the best comprehensive photoelectric performance,and the average transmittance（400⁸00 nm）,the sheet resistance and the figure of merit was 83.90%,3.11Ω/sq and 5.22×10^–2Ω^–1,respectively.Compared with the corresponding regular Ag periodic grid transparent electrode,there had been a considerable improvement in optical transmittance,although the electrical conductivity had a slight loss,so the comprehensive photoelectric performance was greatly improved.2.The 300-nm-thick Ag films deposited on glass substrates by radio frequency（RF）magnetron sputtering were localized ablated by the nanosecond pulsed laser,and patterned composite fractal Ag grid transparent electrodes with pattern combination of4-9,4-16 and 9-16 were prepared.The effects of pattern combinations on the photoelectric performance of patterned composite fractal Ag grid transparent electrodes were analyzed systematically and the optimal grid pitch under the optimal pattern combination was also determined.It could be found from the research results that the patterned composite fractal Ag grid would greatly improve the electrical conductivity in the case of a slight loss of optical transmittance on the basis of corresponding regular Ag periodic grid,so as to increase the comprehensive electrical performance to a great extent.The results showed that patterned composite fractal Ag grid transparent electrodes with pattern combination of 4-9 and grid pitch p?of 1.1mm had a figure of merit of 5.17×10^–2Ω^–1,an average transmittance（400⁸00 nm）of81.09%and a sheet resistance of 2.38?/sq,and then exhibited the optimal comprehensive photoelectric performance.Besides,compared with the corresponding regular Ag periodic grid transparent electrode,the comprehensive photoelectric performance of the patterned composite fractal Ag grid transparent electrode was greatly improved due to the obvious increase in electrical conductivity but a slight sacrifice in optical transmittance.3.Ag films（800 nm）deposited on the glass substrate was selectively ablated by nanosecond pulse laser,then periodic fractal Ag grid transparent electrodes（periods of 4 and grid pitch p of 0.7 mm）and patterned composite fractal Ag grid transparent electrodes（pattern combination of 4-9 and grid pitch p?of 1.1 mm）were prepared for investigating the regulation law of grid thickness matching relations to the photoelectric performance of the fractal metal grid transparent electrodes.The experimental results indicated that periodic fractal Ag grid transparent electrode with the grid thickness t₁ of 500 nm showed the highest figure of merit(16.03×10^–2Ω^–1),and the average transmittance and sheet resistance of which was 84.22%and 1.12?/sq respectively.The patterned composite fractal Ag grid transparent electrode with the grid thickness t₂ of 500 nm exhibits the optimal comprehensive photoelectric performance with a figure of merit of 15.41×10^–2Ω^–1,an average optical transmittance（400⁸00 nm）of 81.70%and a sheet resistance of 0.86?/sq.Compared with the regular Ag periodic grid transparent electrode with a grid thickness of 800 nm(12.16×10^–2Ω^–1),the comprehensive photoelectric performance of the two fractal Ag grid transparent electrodes with different grid thickness had been improved effectively.