Along with the well-known enemies of solar cell efficiency such as dust and pollen, a known unknown recently popped up when researchers began to realize that traces of residue left over from the manufacturing process can reduce the efficiency of solar cells, long before they are exposed to the harsh realities of the outdoor environment. Well, it looks like we can take the “unknown” out of the equation, as researchers from Argonne National Laboratory have just announced that they have nailed the culprit.
Solar Power Cheaper Than Fossil Fuels
The residue issue involves organic photovoltaics (OPVs), a next generation class of solar cells that can be made from cheap, abundant materials. In contrast to silicon, which is a metalloid, OPVs are based on organic polymers, aka plastic.
Although OPVs are less efficient at converting sunlight than silicon, the low cost of the materials partly offsets that factor.
Another offsetting factor is the manufacturing process for OPVs, which is far cheaper than fabricating silicon solar cells. Generally, OPVs can be applied to any flexible, lightweight substrate using standard, high-volume manufacturing processes such as spray-painting or roll-to-roll fabrication.
A third factor is the range of applications that OPVs can have in terms of building integrated solar power, including transparent solar cells that can replace window glass.
Despite all these advantages, the relatively low conversion efficiency of OPVs is still a stumbling block, and in order to keep costs trending downward researchers need to pack greater efficiency into a smaller space, making a solution to the residue issue all the more imperative.
A Key To Solar Cell Efficiency
One step in the right direction occurred when researchers realized that there was actually an OPV residue issue; namely, that nanoscale bits of the catalyst used in the manufacturing process (typically the metal palladium) were probably left in the finished product.
That would reduce efficiency by trapping some of the electric charge generated by the solar cell, and to make matters worse, it also creates a note of uncertainty in commercial solar cell performance, since the amount of residue would be expected to vary from one batch to another.
That made identifying the residue all the more imperative, but for a while researchers were at a loss to find equipment delicate and detailed enough to do the job.
The breakthrough came when a research team guided by Seth Darling of Argonne National Laboratory hit upon the idea of setting the lab’s Advanced Photon Source (APS) loose on the problem.
APS, which has been undergoing an eight-year upgrade project, is billed as the provider of the “brightest storage ring-generated x-ray beams in the Western Hemisphere.”
As described by Argonne writer Jared Sagoff, Darling’s team used high-intensity X-rays from APS to create a fluorescent effect, similar to the way that crime scene investigators use fluorescent equipment to sweep a dark room for mystery liquids and other substances.
With the evidence gleaned from APS, the team identified and quantified traces of a catalyst used during the manufacturing process (that would be the aforementioned metal, palladium).
We Built This!
This discovery is no laboratory hothouse flower. According to Sagoff, the photovoltaic industry is already beginning to make chemical and process adjustments to help reduce residue, in advance of new developments that could prevent it altogether.
So, fellow taxpayers, let’s all pat ourselves on the back for funding yet another shared public research facility that would be impossible to build with private sector dollars, but which directly benefits U.S. companies and improves their prospects for competing in global markets.
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