The usual solar cell is made of silicon. The better cells use the crystalline form of the element, but there are other methods to obtain electric energy from the sun using silicon. Forming silicon crystals, though, can be expensive so there is always interest in different solar technologies. Perovskite is one of the leading candidates for supplanting silicon. Since they use lead salts, they are cheap and simple to construct. The efficiency is good, too, even when the material is not particularly well ordered. The problem is every model science has on what should make a good solar cell predicted that orderly compounds would perform better, even though this is not true for perovskite. Now scientists at Cambridge think they know why these cells perform even in the face of structural defects.
Perovskites take their name from a natural mineral that has the same atomic structure. In 2009, methylammonium lead halide perovskites were found to act as solar cells. Conversion rates can be as high as 25.5% according to sources and — apparently — the cells could be as much as 31% efficient, in theory. Solar cells top out — again, in theory — at 32.3% although in the real world you are lucky to get into the high twenties.
Continue reading “Perovskites Understood”
Regardless of appearances, almost all scientific progress comes at a price. That which is hailed as a breakthrough technology that will save the planet or improve the lots of those living upon it almost always comes at a cost, which sometimes greatly outweighs the purported benefits of the advancement.
Luckily, though, solving these kinds of problems is what scientists and engineers live for, and in the case of the potentially breakthrough technology behind perovskite solar cells (PSCs), that diligence has resulted in a cleaner and safer way to manufacture them. We’ve covered the technology of perovskites in the past, but briefly, as related to photovoltaic cells, they’re synthetic crystals of organometallic cations bonded to a halide anion, so something like methylammonium lead tribromide. These materials have a large direct bandgap, which means a thin layer of the stuff can absorb as much solar energy as a much thicker layer of monocrystalline silicon — hence the intense interest in perovskites for cheap, easily manufactured solar cells.
The problem with scaling up PSC manufacturing has been the need for volatile and dangerous solvents to dissolve the perovskites. One such solvent, dimethylformamide (DMF), commonly used in pharmaceutical manufacturing and often a component of paint strippers, is easily absorbed through the skin and toxic to the liver in relatively low concentrations. Another common solvent, γ-butyrolactone (GBL), is a precursor to γ-hydroxybutyric acid (GHB), a common recreational club-drug known as “liquid ecstasy”.
In a recent paper, [Carys Wrosley] and colleagues at Swansea University showed that γ-valerolactone (GVL), a far less toxic and volatile solvent, could be effectively substituted for DMF and GBL in perovskite manufacturing processes. One of the most promising features of perovskites for solar cells is that the solution can be easily applied to transparent conductive substrates; the use of GVL as a solvent resulted in solar cells that were comparably efficient to cells made with the more dangerous solvents.
Continue reading “Better Solvents Could Lead To Cleaner, Greener Perovskite Solar Cells”
If you’ve been around long enough, you’ll know there’s a long history of advances in materials science that get blown far out of proportion by both the technical and the popular media. Most of the recent ones seem to center on the chemistry of carbon, particularly graphene and nanotubes. Head back a little in time and superconductors were all the rage, and before that it was advanced ceramics, semiconductors, and synthetic diamonds. There’s always some new miracle material to be breathlessly and endlessly reported on by the media, with hopeful tales of how one or the other will be our salvation from <insert catastrophe du jour here>.
While there’s no denying that each of these materials has led to huge advancements in science, industry, and the quality of life for billions, the development cycle from lab to commercialization is generally a tad slower than the press would have one believe. And so when a new material starts to gain traction in the headlines, as perovskites have recently, we feel like it’s a good opportunity to take a close look, to try to smooth out the ups and downs of the hype curve and manage expectations.
Continue reading “Perovskites: Not Just For Solar Cells Anymore”