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Transparent Conducting Oxide

National Renewable Energy Laboratory

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<em>Transparent Conducting Oxides (TCOs) have varying optical and electrical qualities. The optimal TCO for photovoltaic applications is one that maximizes both optical transparency and electrical conductivity as both of these attributes contribute to greater photoelectric energy conversion. </em><br />
Transparent Conducting Oxides (TCOs) have varying optical and electrical qualities. The optimal TCO for photovoltaic applications is one that maximizes both optical transparency and electrical conductivity as both of these attributes contribute to greater photoelectric energy conversion.

Technology Marketing Summary

Transparent conducting oxides (TCOs) are utilized in a wide range of opto-electronic applications such as the manufacture of LCDs, touch panel devices, window coatings, and photovoltaic solar cells. Manufacturing involves depositing a metal oxide as the thin film on top of a substrate. Achieving the desired opto-electronic properties of the thin film is typically dependent on the amount of oxygen introduced during the deposition process as it produces a tradeoff between electrical conductivity and optical transparency. NREL scientists have developed a TCO thin film material which has enhanced optical properties without substantially decreased electrical conductivity.

Tin oxide coated glass, typically doped with fluorine, is the most common TCO in terms of production volume and is currently used in the production of low-emissivity glass, thin film Si- and CdTe-based PV devices. The main advantages to using tin oxide are that it contains neither scarce indium nor toxic cadmium, and the optical and electrical properties remain stable in high temperature processing. Other benefits include long-term environmental stability and chemical resistance. However, tin oxide does not typically yield electron mobilities as high as that of indium oxide or cadmium oxide, and therefore a higher charge carrier concentration is necessary to achieve similar conductivity. The problem is that increasing charge carrier concentration reduces optical transmission at longer wavelengths due to the absorption by the free carriers.  The invention is a new thin film material which is able to achieve increased transmission in the visible to Near Infrared (NIR) spectrum without compromising its electrical conductivity.

Description

The new technology comprises a TCO doped with a high permittivity material. High permittivity materials include materials that produce large values of high-frequency dielectric permittivity when produced as an oxide, such as materials comprising certain metals, rare earth elements, and lathanides, and the oxides of these elements. These high permittivity materials, when utilized with the TCO, display increased transmission in the visible or NIR spectra. The visible spectrum typically includes wavelengths from about 380 nm to about 700 nm, while the NIR spectrum typically includes wavelengths from about 800 nm to about 2500 nm. In addition, the visible-to-near infrared (vis-NIR) region typically includes wavelengths from about 380 nm to about 2500 nm. The phrase "increased transmission" refers to an increase in optical transmittance at a particular range of wavelengths in comparison to a reference film. For example, a Zr-doped FTO film's increased transmittance at a particular range of wavelengths is determined with reference to the transmittance of an FTO film that does not contain a Zr addition, over the same range of wavelengths, but otherwise demonstrates similar electrical properties and thickness. In certain embodiments, the films exhibit an increased transmittance over 380 to 1200 nm, but may also exhibit increased transmittance over any wavelength range with the visible, vis-NIR or NIR spectra.

Benefits
  • Increased light absorption
  • Inexpensive and non-toxic materials
  • Long-term durability
Applications and Industries
  • PV cell manufacturers
  • Smart glass manufacturers
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Date
Patent 8,734,621
Patent
8,734,621
Transparent conducting oxides and production thereof
Transparent conducting oxides and production thereof are disclosed. An exemplary method of producing a transparent conducting oxide (TCO) material may comprise: providing a TCO target (110) doped with either a high-permittivity oxide or a low-permittivity oxide in a process chamber (100). The method may also comprise depositing a metal oxide on the target (110) to form a thin film having enhanced optical properties without substantially decreasing electrical quality.
05/27/2014
Issued
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL 04-11PrototypeAvailable07/28/201407/28/2014

Contact NREL About This Technology

To: Bill Hadley<Bill.Hadley@nrel.gov>