Lead halide perovskites are promising photovoltaic materials with solar conversion efficiencies comparable to that of commonly used silicon. A constraint to its use in solar cells is the instability of different phases of the material at room temperature, and the tendency for these phases to transform into a nonfunctional state. Researchers from Stanford University and the U.S. Department of Energy’s SLAC National Accelerator Laboratory developed a method to manipulate the material to restore and preserve photovoltaic functionality.

The solution entails use of a diamond anvil cell to subject the unstable yellow phase crystals of the perovskite to high pressure and a temperature of 450° C. The treatment converts the material into the desirable and efficient black phase crystals that remain functional at room temperature and in humid air for 30 days or longer.

The pressure needed to turn the crystals black and keep them that way was roughly 1,000 to 6,000 times atmospheric pressure. The shift in the crystal structure was confirmed by synchrotron X-ray diffraction and Raman spectroscopy measurements.

The researchers plan to scale up the process described in Nature Communications to bring it within the realm of manufacturing.

Squeezing a promising lead halide material in a diamond anvil cell (left) produces a black perovskite (right) stable enough for solar power applications. Source: Greg Stewart/SLAC National Accelerator Laboratory