NRL is seeking conditions that would speed up crystal formation by varying the amounts of chlorine in substitution for iodine and adding a "negative solvent” that will cause the perovskite to settle out of solution faster. The result, thus far, is a substance that takes only one minute at 100°C to dry onto a surface: fast enough to achieve rapid and cost-effective “roll to roll” manufacturing onto sheets. The solar cells prepared using this perovskite “ink” have a measured efficiency of 17 percent, with levels reaching 19 percent with an additional coating of fullerenes.
The benefits from the new ink, according to the NREL team, include a long time-window of precursor film processing—up to about eight minutes—and a rapid one-minute rate of perovskite grain growth, which greatly increases the method’s reproducibility and production rate and gets it closer to suitability for mass production.
Dr. Kai Zhu, senior scientist at the Chemistry and Nanoscience Center at NREL, told Design News that with the longer processing window, the researchers were able to decouple the precursor film deposition step from the perovskite crystallization and grain growth.
“This has enabled us to use blade coating (which is one of the scalable deposition techniques) to coat perovskite film uniformly over large-area substrates,” said Dr. Zhu. “Finally, using blade-coated absorbers, we achieved a lab-scale (0.1 cm2) device with stabilized efficiency of more than 19 percent and a 12.6-cm2 four-cell module with 13.3 percent stabilized active-area efficiency output.”
The team will continue its research with perovskite solar cells and pursue new avenues of material synthesis, interface design, device physics, fundamental characterizations, scalability and stability issues, as the latter remains a problem with perovskite materials.
“Recent results from the research community (including our own studies) have shown promise that with fine tuning of perovskite compositions, device architecture, interface properties, the stability of perovskite solar cells can be much improved,” Dr. Zhu told Design News. “Our aim is to push perovskite-based materials and technologies with an emphasis on creating a foundation for bringing perovskite PV to market.”
The researchers’ study, “Perovskite Ink with Wide Processing Window for Scalable High-Efficiency Solar Cells,” was published in the journal Nature Energy .