Added to cells of the ‘MAPbI3‘ perovskite structure, by alternately depositing thin layers of MAPbI3 and CsI, atoms from Cs migrate and become intercalated into the crystal lattice (see diagram).
“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, with what the team described as a “double layer CsI layer” has power conversion efficiency as high as 18.43% and far increased moisture resistance (see graph). Stored in the dark at 40–50% relative humidity for >4000 hours, it retained over 83% of its initial efficiency, according to a paper published in Science Direct (see below).
The researchers “hypothesise 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.
The work is covered in Science Direct as ‘Double-layer CsI intercalation into an MAPbI3 framework for efficient and stable perovskite solar cells‘