Schematic of the perovksite material

Image: University of Cambridge

A team led by researchers at the University of Cambridge in the United Kingdom has demonstrated layer-by-layer (LbL) vapor-phase-based growth of halide perovskites, specifically cesium, lead, bromine (CsPbBr3) grown on a two-dimensional (2D) perovskite single crystal. The 2D substrate was PEA2PbBr4, with PEA being an acronym for 2-phenylethylammonium.

“The resulting CsPbBr 3-PEA 2 PbBr 4 heterostructure exhibited angstrom-level precise and uniform layer thickness down to monolayer, which is important for quantum-confined applications,” said the researchers in “Layer-by-layer epitaxial growth of perovskite heterostructures with tunable band offsets,’ published in Science.

“The hope was we could grow a perfect perovskite crystal where we change the chemical composition layer by layer and that’s what we did,” said co-first author Yang Lu in a statement. “It’s like building a semiconductor from the ground up, one atomic layer after another, but with materials that are much easier and cheaper to process.”

Highlighting that the process is scalable, solvent-free, and industrially compatible, the scientists stated that to their knowledge, it was a first for such precise LbL growth in perovskite-related heteroepitaxy.

There is potential for the technology in solar PV processing, among other optoelectronic applications, according to the corresponding author of the study, Samuel Stranks. “For depositing perovskites, vapor equipment is commercially available, brought online over the last 5 years or so, and more options are coming onto the market, with increasing traction from both academia and industry,” Stranks told pv magazine, noting that the research opens up new approaches for further improving and stabilizing PV.

The group is now trying to make these sandwich structures into multi-layer structures, and demonstrate them in “fully functioning” devices, such as solar cells, light-emitting diodes (LED), radiation detectors and quantum devices, according to Stranks.

The paper highlighted that uniform thickness control enables “tunable band offsets, overcoming key limitations of solution-based synthesis.” 

It said that combining “computational simulations and optical spectroscopic measurements” helped to show that large band offset shift could be achieved by “precisely controlling the interfacial structure through tuning the deposition conditions, allowing either type I or type II heterojunctions and enabling tailored charge transport and recombination dynamics.”

The heteroepitaxial templating also enabled a reduction in defect densities, enhanced carrier transport, and it resulted in higher photoluminescence quantum yields (PLQY) in the CsPbBr 3 layer, according to the research.

After experimenting with depositing CsPbBr 3 on several other types of 2D substrates, the researchers said they anticipate that LbL epitaxy can be “extended to other halide systems as well,” but cautioned that when it comes to iodide perovskites, further phase management research is required “to allow the desired phase formation under the growth conditions.”

The UK researchers were joined by teams from AMOLF in the Netherlands and the University of Colorado, Boulder in the US.