A Perovskite solar cell stack developed by Princeton University is expected to enable outdoor life for at least five years and maybe up to thirty years!
Between the hole transport layer and the photon-absorbing perovskite layer, there must be a 2D material barrier layer. “While the idea of a 2D capping layer isn’t new, it is still considered an emerging technique,” according to the University. With a copper thiocyanate hole-transport and a caesium lead tri-iodide (CsPbI3) absorber, the cells are entirely inorganic.
According to Princeton University, researcher Xiaoming Zhao and associates were developing and testing “scores of permutations” of layer chemistries and geometries to maximise light absorption while guarding the delicate areas of the stack against deterioration. They discovered that a two-dimensional Cs2PbI2Cl2 layer increased conversion efficiency from 14.9 to 17.4% and stabilised the absorber/hole-transport interface, extending life. “There was basically zero [efficiency] drop after nearly half a year,” said Zhao.
The lab was searching for a realistic accelerated life test at the same time, and it decided to use heat, humidity, and light exposure as accelerators. Samples were immersed for four hours at temperatures ranging from 0 to 110 °C. According to a publication about them in Science, devices with the 2D layer did not degrade at 35°C and would maintain 80% of initial efficiency after over 2,100 hours at 110°C under steady illumination.
According to the paper, Arrhenius temperature dependence was found and used to forecast an intrinsic lifetime of 51,000 7,000 hours, or nearly six years, if operated constantly at 35°C. According to colleague Professor Lynn Loo, that is the equivalent of 30 years of outdoor operation at a place like Princeton. “We might have the record today, but someone else is going to come along with a better record tomorrow,” she said, “The really exciting thing is that we now have a way to test these devices and know how they will perform in the long term.”