Perovskites hold potential to provide low cost solar energy. There is a dirty little secret, however, to this version of clean energy. Currently, the best perovskite solar technology is lead-based. As with other products (think paint, gasoline, etc.), lead is not what would be considered an ideal material due to its toxicity. Recent success with tin is promising a more “ideal” future.
Tin-based perovskites are getting a lot of positive press even though they only convert about 6% of solar energy to electricity. Silicon solar cells have efficiencies somewhere around 20-25% and lead-based perovskites are now pushing 20%. So what’s so exciting about 6%?
The exciting aspect of these modestly effective solar materials is simply that they are not lead-based. The important backstory which puts this excitement in perspective is that perovskites have made leaps and bounds in efficiency much more rapidly that their silicon counterparts and also are relatively cheap. The buzz, then, is based on the expectation of future progress.
Broadly speaking, perovskite describes the structure of the compound, which resembles the CaTiO3 mineral bearing the same name. The general recipe for this structure involves atoms with suitable cationic size differences and electronic properties. Lead has specific properties which make it particularly effective. Like lead, tin is a group 14 element, and therefore a close relative and viable replacement.
Unfortunately, switching to tin is not all wine and roses. The tin-based perovskites tend to be less stable and require special processing in an inert environment. The technology exists to manufacture these materials and once hermetically sealed for final use, the cells should be stable. How they will perform over the span of decades is less certain. Longevity, not just efficiency, is expected to be a key area of research as well.
Although the lead used in the most efficient perovskite solar cells may not leech into the environment once packaged for use, it seems good practice to seek alternative materials now. Clean energy production which relies on potentially hazardous materials during manufacture and while in service is somewhat contradictory. Given the demand for better alternative energy sources, it is well worth the effort to examine the potential in cleaner materials, even if they have a way to go.
Below is a general video about perovskite solar cells put out by the American Chemical Society for more information.
Images courtesy of Banda Solar