Researchers from Kanazawa University in Japan have found that the addition of cesium iodide can improve the stability and efficiency of certain perovskite solar cells. Added to MAPbI3 cells by alternately depositing thin layers of MAPbI3 and CsI, atoms from Cs migrate and become intercalated into the crystal lattice.

“Our approach allowed us to produce layers with precise control over the CsI intercalation,” said researcher Tetsuya Taima. Using this control, different Cs-inclusive perovskite crystals were created.

One certain specimen, with what the team described as a “double layer CsI layer”, reached power conversion efficiency as high as 18.43% and far increased moisture resistance. Stored in the dark at 40–50% relative humidity for >4000 hours, it retained over 83% of its initial efficiency.

The researchers “hypothesize that the intercalation of cesium reduces the spacing between the atomic planes, so that moisture from the air cannot intrude as easily,” according to the university. “Also, the surfaces become smoother, which allows charges to reach the electrodes.”

Scanning electron microscopy showed that crystal grains inside the material had increased from 300 to 700nm.