Recent progress in transparent conducting materials by use of metallic grids on metaloxides
- PDF / 199,891 Bytes
- 5 Pages / 432 x 648 pts Page_size
- 89 Downloads / 226 Views
Recent progress in transparent conducting materials by use of metallic grids on metaloxides Joop van Deelen*1, Henk Rendering1, Arjan Hovestad1 1 Netherlands Organization for Applied Scientific Research (TNO), PO Box 6235, 5600 HE Eindhoven, The Netherlands, *corresponding author: [email protected] ABSTRACT Alternatives to ITO are under heavy investigation. Organic and inorganic transparent conducting materials are compared based on their transparency versus sheet resistance characteristics. Although graphene has advanced recently, TCOs are still superior in performance and can only be surpassed by the combination of transparent materials with a metal grid. Results on modeling and design optimization using a monolithically integrated CIGS cell configuration as case showed that considerable efficiency enhancement (up to 17% in power output compared to single TCOs) can be achieved for metal grid/TCO combinations. Conductivity improvement has been experimentally verified by four point probe measurements.on both commercial ITO coated PET foil as well as on ZnO coated glass with electrochemically deposited metal grids Sheet resistances as low as 0,1 Ohm/sq were reached and 80 times and 400 times conductivity improvements were obtained at a transparency loss of only 3% and 6%, respectively. It was also found that electrochemical deposition results in more conductive grids than obtained by Ag-ink screen printing due to higher aspect ratios and bulklike conductivity of the first. Simultaneously, nanopatterning allows optimal grid width of 20 μm, as determined by modeling. INTRODUCTION Transparent conductors are under intense research, because new materials and processes are becoming available that could serve as an alternative to ITO, which is commonly applied in displays. ITO is one of the best transparent conductors, but indium is quite expensive. Cheaper alternatives, such as fluor doped SnO2 and aluminum doped ZnO (AZO) are the most widely used for thin film solar cells. In spite of their popularity, TCOs have some major drawbacks. For all TCOs, including SnO2 and ZnO, the limited transparency in the infrared and the brittleness are the main concerns [1, 2]. As a result, alternatives for TCOs have been explored. For example, thin metal sheets, graphene and carbon nanotubes can function as transparent conductors. In this work, a comprehensive overview will be given on the status of these materials. In short it can be noted that for these materials, layer thickness higher than a few nanometers reduces the transmittance dramatically, limiting the optoelectronic device output when these materials are used.
17
In many cases, the relation between the transparency (T) and the resistivity (Rs) of a material can be described by a rather simple equation containing the ratio of the optical conductivity op and the dc conductivity DC [3] § 1 T = ¨¨1 + © 2 Rs
μ 0 σ op · ¸ ε 0 σ dc ¸¹
−2
§ 188(Ω) σ op · ¸ = ¨¨1 + Rs σ DC ¸¹ ©
−2
(1)
In which the free space permeability μ0 = 4 π × 10-7 s2/Fm and permittivity ε0 = 8.854 × 1
Data Loading...
