This year, the race regulations are a clear sign of how rapidly solar technology is changing. Teams have to use a smaller solar collector than before: cars in the Challenger class can have no more than 43 square feet of solar cells versus nearly 65 square feet for the previous race, in 2015. That’s half the area allowed on cars from the original 1987 race. In other words, technology is advanced enough now (both in solar cells and the underlying vehicle designs) that you don’t need a sea of panels to keep a car running.
The Oxford team, led by physicist Henry J. Snaith, made their solar cells using perovskites, a class of mineral-like crystalline materials that has recently grabbed much attention among researchers in photovoltaics. Perovskites have properties similar to inorganic semiconductors and show sunlight-to-electricity conversion efficiencies of more than 15%.
Stacked solar cells consist of several solar cells that are stacked on top of one another. Stacked cells are currently the most efficient cells on the market, converting up to 45 percent of the solar energy they absorb into electricity.
This should reduce overall costs for the energy industry because, rather than creating large, expensive solar cells, you can use much smaller cells that produce just as much electricity by absorbing intensified solar energy from concentrating lenses. And concentrating lenses are relatively inexpensive,
Like any other new entrant into the highly competitive solar-panel market, perovskites will have difficulty taking on silicon solar cells. The costs of silicon solar cells are falling, and some analysts think they could eventually fall as low as 25 cents per watt, which would eliminate most of the cost advantage of perovskites and lessen the incentive for investing in the new technology. The manufacturing process for perovskite solar cells—which can be as simple as spreading a liquid over a surface or can involve vapor deposition, another large-scale manufacturing process—is expected to be easy. But historically, it has taken over a decade to scale up novel solar-cell technologies, and a decade from now silicon solar cells could be too far ahead to catch.
In 2009, researchers at Rutgers University in Piscataway, New Jersey, demonstrated2 that the material has a photovoltaic response to visible light — meaning that when it is hit by light, a voltage is created. The size of the voltage depends on which polarization state the material is in, and can be read out using electrodes or transistors. Crucially, shining light on the material doesn’t change its polarization, and so does not erase the data stored in it.
It takes less than 10 nanoseconds to write to and read the cells, and recording the data requires about 3 volts. The leading nonvolatile RAM technology, flash, takes about 10,000 times longer to read and write, and needs 15 volts to record.
Conventional materials that turn light into electricity, like silicon and gallium arsenide, generate a single electron for each photon absorbed. Since a photon contains more energy than one electron can carry, much of the energy contained in the incoming light is lost as heat. Now, new research reveals that when graphene absorbs a photon it generates multiple electrons capable of driving a current. This means that if graphene devices for converting light to electricity come to fruition, they could be more efficient than the devices commonly used today.
Researchers led by Xiaolin Zheng, a professor of mechanical engineering at Stanford University, demonstrated a way to transfer the active materials of the solar cell from a rigid substrate onto another surface, such as a sheet of paper or plastic, the roof of a car, or the back of a smartphone. As with other solar cells, wires would then be connected to deliver power, but flexible solar cells could be used on curved surfaces, and, because they’re lightweight, they would be easier to install than conventional panels.