So what happened? (Actually, a more accurate question may be “so what didn’t happen?”)
Currently, the push to advance the technology toward achieving its vast potential is being carried out primarily on two fronts. Companies who back conventional silicon cell technology are mostly betting that efforts to boost efficiency can eventually offset the financially and energy intensive manufacturing process that, thus far, has hindered any opportunity for wider adoption among consumers. Meanwhile, modest, yet steady progress is also being made on polymer-based organic cells, which are cheaper to produce and more flexible, but are fragile and much less efficient.
Now, British researchers at the University of Sheffield have developed a new type of solar panel that may bring the beleaguered industry one huge step closer to that long sought after tipping point. And interestingly enough, the technology isn’t so much a discovery, but rather a possibly groundbreaking amalgamation of two of the biggest recent breakthroughs in the field.
Still, the devices that David Lidzey, physics professor and lead researcher, have fashioned in his lab aren’t anywhere near being ready for prime time. They’re quite rudimentary, comprised of little more than sheets of transparent metal coated with a brownish light-absorbent substance. But what’s important to note here is that the methods used to create them are meant, in principle, to remove an often cited barrier adoption: cost.
Typically, producing the kind of purified crystalline silicon suitable for panels involves baking silicate rock at temperatures reaching upwards of 1,000 degrees Celsius, a process that requires costly amounts of energy. In contrast, the technique that Lidzey and his team developed was adapted from a “spray-painting” technique that enables organic semiconductors to be applied in a less heat intensive manner as well as onto various types of surfaces such as glass, plastic and steel. Researchers at Australia’s national science agency, CSIRO, have spent the last seven years working on something fairly similar.
“We use an ultra-sonic spray-coating machine, which allows us to carefully deposit layers having a controlled thickness,” he explained. “Such layers often have to be heat-treated, but at low temperatures, less than 100 degrees Celsius, to make them function in the correct way.”
And instead of using low-efficiency polymers, the sheets are sprayed with perovskite, dark, crystal-shaped compounds that, as of late, have become the darling of materials scientists. Besides being abundant and relatively cheap to cook up at lower temperatures, the calcium titanium oxide mineral possesses unique light-absorbing properties that trap energy from both visible and infrared light very efficiently. In just the five years since the first perovskite cells were tested, conversion rates have reached roughly 18 percent, nearly on par with silicon cells. Lidzey’s perovskite cells come in at 11 percent efficiency.
Still, the underlying technology has a number of kinks that need to be worked out. For instance, perovskite works only on flat sheets since uneven surfaces may cause the fragile material to wear quickly. The most efficient crystals also contain toxic lead chloride, though Lidzey says they can still work well enough if the harmful bits are replaced with the right substitute. And with perovskite pigments, energy conversion rates can differ from cell to cell, due to the crystals’ tendency to form in varying shapes. Subsequent investigations into how this occurs, he says, could lead to insights into how to to make the process more uniform.
“There are a lot of issues still to solve, but the most critical of these are increasing the life span of perovskite devices so they can work without degradation for many years,” he says.
“Presently,” he adds, “silicon cells can work for 25 years. We’ve already seen some degradation with our devices after a few thousand hours under simulated sunlight, so approaching this will be a very big challenge.”
Despite the hurdles, Lidzey remains confidant in the long term viability of his work. He’s currently collaborating with companies that use spray-coating for other applications to refine his own approach. Ultimately, he says, “it is important to make sure that what we can do in our lab can be easily translated to a manufacturing environment.”