Scientists from Taiwan's Industrial Technology Research Institute (ITRI) and National Yang Ming Chaio Tung University recently demonstrated a way to produce high-purity lead-iodide, as a precursor material for a perovskite solar cell. The team used temperature to better control the orientation of crystals, and managed to show much higher efficiencies when the precursor was used to fabricate a perovskite layer and subsequently a working solar cell.
The team worked on the fabrication of lead-iodide (PbI2), an element used in many of the highest-performing perovskite solar cells produced to date. They built on earlier research that has shown the purity and formation of this material could be a key factor in performance once it is integrated into a solar cell. The group’s recent work demonstrates how the crystalline structure and orientation of PbI2 have a significant impact on cell performance. The researchers also introduce a simple way to control this using temperature during synthesis.
By varying the temperature during synthesis of PbI2 the group noted significant changes in the way the crystals formed, and these had a major effect on the cell performance. “Horizontal planes … are beneficial for black FAPbI3 perovskite crystals while the lateral facets … lead to the formation of δ-FAPbI3 which is known as the yellow phase of perovskites and has no photo-activity,” the group explained.
And when fabricated into cells, PbI2 synthesized at higher temperatures (120 C) was the top performer, with the temperature causing more growth of the desired horizontal facets. Cells made with PbI2 synthesized at 25 C came out at just 8.8% average efficiency, while those with the material processed at 120 C reached an average efficiency of 17%, with a champion cell in the batch measured at 17.96%. And these cells were scaled up to an area of 3.68 square centimeters, achieving 16.08% efficiency, which the group sees as strong potential for its approach to be worth investigating for larger area devices.
“The industrialization of perovskite modules is inevitable,” the group concluded. “Providing reliable and cheap precursors is the key to fabricate PSCs as a competitive product in the solar cell market in the future.”