A new international study led by chemists at the Georgia Institute of Technology has observed that hybrid organic-inorganic perovskites (HOIPs) possessed a “richness” of semiconducting physics created by what could be described as electrons "dancing" on wobbling chemical underpinnings. That contradicts established semiconductors that rely upon rigidly stable chemical foundations, or quieter molecular frameworks, to produce the desired quantum properties. This could mean that HOIPs may be used in the future as semiconductors with nuanced colors emanating from lasers, lamps, and even window glass.
HOIPs have been reported by the team to be quite challenging to examine, but the researchers from a total of five research institutes in four countries succeeded in measuring a prototypical HOIP and found its quantum properties on par with those of established, molecularly rigid semiconductors, many of which are graphene-based. “We don’t know yet how it works to have these stable quantum properties in this intense molecular motion,” said first author Felix Thouin, a graduate research assistant at Georgia Tech. “It defies physics models we have to try to explain it. It’s like we need some new physics.”
“The properties were at least as good as in those materials and may be even better,” said Carlos Silva, a professor in Georgia Tech’s School of Chemistry and Biochemistry. Not all semiconductors also absorb and emit light well, but HOIPs do, making them optoelectronic and thus potentially useful in lasers, LEDs, other lighting applications, and also in photovoltaics. The lack of molecular-level rigidity in HOIPs also plays into them being more flexibly produced and applied.
Despite HOIP’s wobbling, it’s also a very ordered lattice with its own kind of rigidity, though less limiting than in the customary two-dimensional materials. "It’s not just a single layer,” the researchers said. “There is a very specific perovskite-like geometry”. “The lattice self-assembles, and it does so in a three-dimensional stack made of layers of two-dimensional sheets. But HOIPs still preserve those desirable 2D quantum properties.”
Those sheets are held together by interspersed layers of another molecular structure that is a bit like a sheet of rubber bands. That makes the scaffolding "wiggle". “At room temperature, the molecules wiggle all over the place. That disrupts the lattice, which is where the electrons live. It’s really intense,” Silva said. “But surprisingly, the quantum properties are still really stable.”
Having quantum properties work at room temperature without requiring ultra-cooling is important for practical use as a semiconductor.
Going back to what HOIP stands for - hybrid organic-inorganic perovskites - this is how the experimental material fit into the HOIP chemical class: It was a hybrid of inorganic layers of a lead iodide (the rigid part) separated by organic layers (the rubber band-like parts) of phenylethylammonium (chemical formula (PEA)2PbI4). The lead in this prototypical material could be swapped out for a metal safer for humans to handle before the development of an applicable material.