Solar Cells of Stainless Steel

Michael A. Greenwood

The ongoing search for less-expensive solar cells has led researchers in Finland to consider a material that is as plentiful as it is durable: stainless steel.

Traditional solar cells use glass as the substrate upon which the rest of the device is built. But sheets of glass are the most expensive component in dye-sensitized solar cells, accounting for as much as 30 percent of the overall material costs.

Researchers used stainless steel substrates in dye-sensitized solar cells to test their performance against solar cells with a traditional glass substrate. Courtesy of Adolfo Vera and Helsinki University of Technology.

Stainless steel is considerably less expensive than its glass counterpart, and it has the added benefit of being easy to mass-produce through roll-to-roll production, according to researcher Kati Miettunen of Helsinki University of Technology in Finland.

To find out how a stainless steel substrate affects a solar cell’s performance, Miettunen and her colleagues fabricated dye-sensitized solar cells with a stainless steel substrate, which they used as both a counter electrode and as a photoelectrode. The team used a traditional glass substrate in a third solar cell that served as a control.

Samples were prepared with 1.25-mm-thick stainless steel. To this, the researchers added porous layers of TiO₂ onto the photoelectrode substrates, then sensitized the TiO₂ in a dye solution. They prepared the counter electrodes using thermal platinization.

They subjected each cell to a solar simulator with halogen lamps that delivered a light intensity equivalent to 1000 W/m². To measure open circuit voltage decay, they illuminated the cells with a 639-nm LED.

They found that the open circuit voltage was about equal in each of the three cell types. In the stainless steel photoelectric cells, the open circuit voltage was –664 ±10 mV; in the cell with the glass substrate, it was –663 ±8 mV.

In terms of how efficiently the cells converted light into usable electricity, the team found that the stainless steel photoelectrode and counter electrode cells achieved efficiencies of 4.7 and 3.5 percent, respectively. The glass cell, meanwhile, achieved an efficiency of ∼5.2 percent.

One concern about the setup was whether stainless steel would negatively affect the cells. They found that the stainless steel photoelectrode does appear to affect the electrochemical function of the dyed TiO₂ layer, decreasing the electron lifetime and the recombination resistance.

Further studies are needed to determine whether this effect is linked with the cell degradation reported in previous studies. Stainless steel, however, did not appear to have this effect in the counter electrode.

Journal of Physical Chemistry C, March 13, 2008, pp. 4011-4017.