Researchers discovered that atomic-level defects in perovskite material can boost the power conversion efficiency of the material significantly.
Perovskites are a promising candidate for high efficiency photovoltaic modules. These materials typically consist of negatively charged iodine or bromine ions and positively charged lead and organic ions. Adjusting the ions in the arrangement can generate wide bandgap perovskites that capture the solar wavelengths that silicon does not efficiently absorb. Therefore, the two materials could be combined in tandem cells to capture even more energy from the Sun.
Researchers from King Abdullah University of Science and Technology have reported that various atomic-scale defects in perovskite solar materials can significantly boost the longevity and electrical output.
Perovskites feature many defects, like when ions are not in their place creating a gap. These gaps are reactive sites which degrade the performance. “Defect passivation is very important for improving the long-term stability of perovskite solar cells,” says Furkan Isikgor, a researcher in Stefaan De Wolf’s group.
The defect sites can be positively or negatively charged depending on which ion is missing. The researchers have shown that a molecule called phenformin hydrochloride (PhenHCl) overcomes this problem. The molecule consists of an electro-positive ammonium head group that can plug negatively charged defects and an electro-negative amine and imine group body to plug positive gaps.
The researchers observed that the PhenHCl boosted the power conversion efficiencies (PCEs) of wide bandgap perovskites from 16.7 percent in untreated cells up to 20.5 percent in treated cells. “Moreover, PhenHCl passivation improves the PCE of textured perovskite/silicon tandem solar cells from 25.4 percent to 27.4 percent,” Isikgor says.
The stability is also improved in treated cells. “Under continuous light soaking, the PhenHCl-passivated device retained 80 percent of its post-burn-in efficiency for around 106 hours of operation,” Isikgor says.
“Our simple holistic defect-passivation strategy has drastically improved the semiconductor quality of solution-processed perovskites,” says De Wolf. “Simultaneously, we are working on further improvements in device performance and stability through extensive outdoor testing,” he adds.
The work is described in the journal Joule.