TCO for Photovoltaics

TCO coatings for thin film solar cells (a-Si, μc-Si and CdTe)

With the surge of photovoltaics (PV) in the world today, solar cell manufacturers are looking for more economical coating solutions for their production lines. Beneq, with its own nAERO® aerosol-assisted pyrolytic deposition method, presents a technically superior and economical coating method for in-line and off-line coated products. nAERO is capable of producing low-haze and high-haze transparent conductive oxide (TCO) coatings, which allows the cell manufacturer to optimize the coating to suit his specific needs and thus maximize the efficiency of the thin film cell.
 

Higher deposition efficiency

Beneq nAERO^® is cost-efficient and atmospheric, two basic factors that make it attractive to industrial production. nAERO is a new technology that benefits from the advantages of conventional spray pyrolysis and CVD coating. The intrinsic process properties enable a high coating growth rate and efficient coating material usage, with a raw material (precursor) yield of up to 30%.

High coating quality

To prove the performance of nAERO TCO, Beneq has commissioned the manufacture of a-Si/μc-Si tandem solar cells made with both nAERO-coated and commercially available TCO glass. The results, of which the external quantum efficiencies (EXE) are presented in the figure below, show that nAERO-coated cells exhibit the same EXE as the commercial TCO glass. Furthermore, nAERO TCO can be adjusted to suit a wide range of requirements and cell types, including Cd-Te. The tandem study was performed by Helmholz-Zentrum in Berlin, Germany.

Comparison of external quantum efficiency (EQE) between a-Si/µc-Si tandem solar cells manufactured using nAERO^® -coated and another commercially available TCO glass.

Optimized coating properties

nAERO produces a pyrolytic TCO hard coating consisting of fluorine-doped tin oxide (SnO₂:F). The coating properties, such as haze, conductivity and transmission, can be adjusted, depending on which type of solar cell is being made.

Underlayer

If needed, an underlayer consisting of SiO_x, SiO₂ or TiO₂ can be added between the electrically active TCO layer and the glass substrate. This underlayer is produced in a process step prior to nAERO coating. The underlayer serves as a barrier layer against sodium diffusion and eliminates iridescence in reflected light.

Coating specifications¹

Type	transparent conductive oxide (TCO)
Chemical composition	SnO2:F (FTO)
Subgroup (based on haze)	low haze	high haze
Haze, D65/10%	1	12 (example)
Transmittance2, average 400-1000 nm (%)	> 83	> 83
Sheet resistance 3 (Ω/□)	12	10
Thickness (nm)	400	750
Uniformity, sheet resistance (deviation)	< 2.0 (Ω/□)
Uniformity, transmission (deviation)	< 1%
Temperable	yes

¹ All properties are nominal and solely applicable to specimens under specific testing conditions. The information is not intended to and does not create any warranties.
² Transmission measured with index matching liquid CH₃I (haze compensation) on 4 mm glass.
³ Measured by 4-point method.

More information

Download TCO for Photovoltaics brochure (pdf).