Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and the Center for Hybrid Organic Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center (EFRC), University of Wisconsin-Madison, University of Colorado Boulder, Duke University and University of Utah have discovered a new process to induce chirality in halide perovskite semiconductors, which could open the door to cutting-edge electronic applications.
The development is the latest in a series of advancements made by the team involving the introduction and control of chirality. Chirality refers to a structure that cannot be superimposed on its mirror image, such as a hand, and allows greater control of electrons by directing their spin. The researchers have been able to create a spin-polarized LED using chiral perovskite semiconductor in the absence of extremely low temperatures and a magnetic field, as was previously reported. The newest advance accelerates the materials development process for spin control.
The key was in introducing a chiral molecule with a different headgroup into the perovskite. The chiral molecule intentionally does not fit into the perovskite lattice but “twists” the structure from the surface. The chiral molecule transfers its properties several unit cells or layers deep into the perovskite structure. This twist can be controlled by employing left- or right-handed chiral molecules into the grain boundaries and surfaces of a perovskite film, which control the spin properties accordingly. Such twisted structures enable unique functionalities for energy applications where spin-control adds additional potential by acting as electronic spin filters.
Md Azimul Haque, the first author of the paper, said introducing chirality to the low-dimensional perovskite semiconductors generally includes a chiral molecule being present in the perovskite lattice, which needs extensive analysis every time one changes the composition of the chiral molecule. The ability of a proximal chiral molecule to transfer its properties without changing the perovskite composition makes the process simple, faster, and less limiting on the composition, he said.
“We can create materials with known properties now with added chirality very easily compared to traditional methods,” said Haque, a postdoctoral researcher. “The next step is to experiment with the materials and incorporate them into new applications.”
Hybrid perovskites refer to a crystalline structure, containing both inorganic and organic components. In other semiconductors, such as those made from silicon, the material is purely inorganic and rigid. Hybrid perovskites are soft and more flexible, “so a twisting molecule on the surface, will extend the effect deeper into this semiconductor than it can in most rigid, inorganic semiconductors,” said Joey Luther, an NREL senior research fellow and corresponding author.
“This is a new way to induce chirality in halide perovskites,” Luther said, “and it could lead to technologies that we can't really envision but might be somewhere along the lines of polarized cameras, 3D displays, spin information transfer, optical computation, or better optical communication—things of that nature.”