Breakthrough synthesis method improves solar cell stability

Solar cell efficiency has soared in recent years due to light-harvesting materials like halide perovskites, but the ability to produce them reliably at scale continues to be a challenge.

Now, a U.S. National Science Foundation-supported process developed by Rice University chemical and biomolecular engineer Aditya Mohite and collaborators at Northwestern University, the University of Pennsylvania and the University of Rennes has yielded 2D perovskite-based semiconductor layers of ideal thickness and purity by controlling the temperature and duration of the crystallization process.

The research instrumentation was supported through NSF's Soft and Hybrid Nanotechnology Experimental Resource, part of the National Nanotechnology Coordinated Infrastructure.

Known as kinetically controlled space confinement, the new process could help improve the stability and reduce the cost of halide perovskite-based emerging technologies like optoelectronics and photovoltaics.

"Producing 2D perovskite crystals with layer thicknesses — or quantum well thickness, also known as 'n value' — greater than two is a major bottleneck," said Jin Hou at Rice, a lead author of a paper about the process published in Nature Synthesis.

As they form into crystals, atoms or molecules arrange themselves into highly organized, regular lattices. Ice, for instance, has 18 possible atomic arrangements, or phases. Like the hydrogen and oxygen atoms in ice, the particles that make up halide perovskites can also form multiple lattice arrangements.

Because material properties are phase-dependent, scientists aim to synthesize 2D halide perovskite layers that exhibit only a single phase throughout. "In traditional methods of 2D perovskite synthesis, you get crystals with mixed phases due to the lack of control over crystallization kinetics, which is basically the dynamic interplay between temperature and time," Hou said. "We designed a way to slow down the crystallization and tune each kinetics parameter gradually to hit the sweet spot for phase-pure synthesis."

The researchers also created a map — or phase diagram — of the process through characterization, optical spectroscopy and machine learning. "This work pushes the boundaries of higher quantum well 2D perovskites synthesis, making them a viable and stable option for a variety of applications," Hou said.