Many applications such as photovoltaics, LEDs and display elements require an electrode with high conductivity and high transmission for their function. The material most commonly used for this is a thin layer of indium tin oxide (ITO). The thickness of the ITO layer is limited on flexible substrates, as the ceramic properties only allow a low degree of flexibility. This means that the lowest possible sheet resistance is approximately 35 Ω/□. With greater thicknesses - and therefore lower surface resistances - the layer will break under flex stress. In addition to ITO, aluminum-doped zinc oxide (AZO) is also a transparent conductive oxide.
Figure 1 shows the ITO film ROWO_TC-125_35.
Figure 1: ROWO_TC-125_35: Tvis (400-800nm) = 81,7%, T550 = 86,3%
For large-area flexible solar cells are significantly lower surface resistances in the range of 7 to 10 Ω/□ with high transmission are required. These properties are achieved with thin silver layers (≈ 10 nm), which have significantly higher conductivity and high flexibility at the same time.
However, they also have a high level of reflection in the visible spectrum and are susceptible to corrosion from environmental influences. If the silver layer is now embedded in transparent conductive oxide layers (D-Ag-D or I-M-I) the reflection can be significantly reduced by their anti-reflective properties. By adjusting the refractive index and the layer thickness, the transmission is noticeably increased. In addition to AZO, typical transparent conductive oxides are oxides of tin, niobium and bismuth.
Figure 2 shows the optical data of the transparent silver electrode ROWOSOL-2.1
Figure 2: ROWOSOL-2.1: Tmean (360-950nm) ≥ 79%, T600 ≥ 86%, R□≤8Ω/□
ROWO offers TSE coatings with transmittances of up to 87 % and sheet resistances down to 6-8 Ω/□ on optical grade PET film. The individual layers can be adapted to the customer's requirements in order to achieve the optimum properties for the respective applications.
Keywords: transparent conductive layers, flexible transparent electrode, transparent silver electrode, TSE, D-Ag-D, I-M-I, transparent conductive oxide, multilayers
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