Researchers from Ulsan National Institute of Science and Technology (UNIST) have reported the deposition of dense and uniform α-formamidinium lead triiodide (α-FAPbI3) films using perovskite precursor solutions dissolved in ethanol-based solvent. This addresses the issue of halide perovskites generally not being completely soluble in most non-toxic solvents.
The research team, led by Seok Sang-il, has worked out an ethanol-based perovskite precursor solution by designing a complex compound structure so that perovskites can be dissolved well in ethanol. In their study, the researchers obtained power conversion efficiencies of 24.3% using a TiO2 electrode, and of 25.1% with a SnO2 electrode.
"It was possible to manufacture a perovskite thin film with high density, uniformity, and excellent crystallinity by optimizing a combination of binders that can control the speed of volatilization with a solvent during coating and thermal treatment," said Seok, a professor of energy and chemical engineering at the Ulsan National Institute of Science and Technology (UNIST).
In October 2021, Seok set a new record of 25.8 percent in the power conversion efficiency of perovskite solar cells by forming a coherent interlayer between electron-transporting and perovskite layers to reduce interfacial defects. Efforts have focused mainly on surface passivation, but passivating the perovskite surface is difficult because surface-treatment agents on the electron-transporting layer may dissolve while coating the perovskite thin film.
"Perovskite solar cell research has focused on improving efficiency and stability, but now it is more important to conduct research on the foundation for commercialization to reduce or eliminate the use of toxic solvents," Seok said. "This study is the starting point for solving such a problem."
The deposition of dense and uniform α-formamidinium lead triiodide (α-FAPbI3) films was possible using perovskite precursor solutions dissolved in an ethanol-based solvent, Seok's team said in the research paper.
The combination of dimethylacetamide (or dimethylsulfoxide) and an alkylammonium chloride in ethanol resulted in the stable solvation of FAPbI3, the paper said, adding that it's possible to form "very dense and uniform" α-FAPbI3 perovskite films with high crystallinity by combining several types of alkylammonium chloride.
Seok's team opened a joint laboratory with South Korea's Hyundai auto group in June 2022 for a three-year study to develop high-efficiency, large-area perovskite-silicon tandem cells and apply them to vehicle roofs containing solar panels, which are a relatively new phenomenon that promises to use renewable energy to add some charge to car batteries.