It doesn't look like much, but the straight line on the graph showing no reduction in electricity production means that the stacked silicon cells on the right are on the verge of changing the world. MK Nazeeruddin/EPFLOne of the last barriers to exceptionally cheap solar power has fallen, a paper in Nature Communications reports. A perovskite solar cell has been demonstrated to work for more than 10,000 hours without loss of performance, despite being exposed to conditions more grueling than on any rooftop. The work greatly increases the chances we will soon see solar panels producing power at prices fossil fuels could never match.
A team led by Professor Mohammad Khaja Nazeeruddin of the École Polytechnique Fédérale de Lausanne, Switzerland, and including solar pioneer Professor Michael Grätzel combined so-called 2D and 3D perovskite technology to produce a 12.7 percent efficient product. That in itself is far from record-breaking, and when scaled up to a 10 x 10 centimeter (4 x 4 inch) module, the efficiency fell to 11.2 percent. Nevertheless, the longevity of their product, losing no measurable performance over more than a year of 24/7 testing, makes it newsworthy, perhaps even world-changing.
Although silicon wafers dominate the solar market, making up 93 percent of solar installed in 2015, they have flaws that are very hard to overcome. The efficiency of the best silicon cells has barely improved for two decades, and the extreme temperatures needed to produce pure silicon crystals puts a floor under the price.
Numerous alternatives have been tried, and a few have even gained some market share, but all have their own problems. In the last few years easily the most excitement has buzzed around perovskite cells, which mimic the structure of calcium titanate (CaTiO3) crystals, but have a range of light-capturing capacities when certain other elements are substituted.
Efficiency records for perovskite cells turning sunlight to electricity have fallen so fast it is hard to keep up, and they can be produced without high-temperature processes or substantial quantities of expensive materials.
One big obstacle has remained to perovskite sweeping the market and undercutting every other power source on price. Early perovskite cells degraded exceptionally quickly when exposed to water, ultraviolet light, or sometimes even air. Their lost performance was so rapid they would be useless commercially, except perhaps in space. Improvements have been demonstrated alongside the dramatic gains in efficiency but questions have remained if they could last long enough to be worthwhile.
Two-dimensional perovskites, made from a single layer of atoms, have shown greater stability than their more efficient 3D equivalents. Nazeeruddin and Grätzel protected a 3D perovskite with a 2D layer and replaced the troublesome hole transporting materials with hydrophobic carbon electrodes, creating a fully printable product that didn't lose performance even when exposed to intense light and 90ºC (194ºF) temperatures.
As soon as this stability can be combined with the efficiency others have achieved, mass roll-out can start to transform the economics of energy.