In 2007, a student at the University of Tokyo brought a lump of a grey, sparkly mineral to his professor Tsutomu Miyasaka, with the hope that this material might have potential to make cheap and efficient solar cells. But it only converted 4 percent of the sun energy to electricity. Not that remarkable.
Now, however, things have changed. Seven years later the unremarkable lump of rock called perovskite is beating out most solar cells on the market, getting 20 percent efficiency. The progress has sped up because researchers around the world saw the potential in this mineral.
While the sun is pretty much a limitless source of energy for all of us, the cost to capture it remains the challenge. The typical residential solar roof might get about 15 percent efficiency in sunlight and provides electricity at 50 cents/watt. This is twice the cost of coal.
So it's got to get cheaper in order to pull ahead as our number one energy source. Right now the top-performing cells, made of gallium arsenide get a maximum efficiency of about 30 percent but are prohibitively expensive.
The cheaper options like copper indium gallium selenide (a flexible material) or cadmium telluride (as cheap as silicon) get only about 20 percent efficiency.
Here is why perovskite is worth watching: It removes the need for a major component of the solar cell makeup.
Standard solar cells require a semiconductor (like silicon) to absorb sunlight and produce electrons and their opposite counterpart, holes. Then the cell separates the electrons and holes to create a flow of charged particles...and this is the electric current. Few materials can both absorb light in the right way and separate the electrons, so there needs to be a pigment added to the semiconductor that absorbs sunlight at just the right wavelength. The breakthrough with perovskite is that it does not require a semiconductor. Scientists are not yet sure how it works but apparently this material can shift electrons and holes better on its own, as opposed to a paring with silicon or some other semiconductor.
Scientists have shown that perovskite can be manufactured cheaply and easily, and Henry Snaith, a TK at the University of Oxford, hopes to bring this material to market by 2016. They think they can reduce the price to 10 cents a watt.
There are two main challenges. First, perovskite contains lead and so scientists are experimenting with tin-based versions that look very promising so far. The second challenge is pretty tough to solve: Perovskite easily absorbs moisture and when it's exposed it tends to swell and loses its ability to absorb light. Since the very utility of solar cells requires that they are exposed—researchers note they can be encased in glass.
If these issues can be resolved, it is possible, theoretically, that there could be terawatts of perovskite cells, and those kinds of numbers would easily dwarf the current silicon industry.