Layering a perovskite material onto a substrate of alternating metal–dielectric layers dramatically increases the light conversion efficiency of the material. [Image: C. Zhang, University of Rochester]
The light conversion efficiency of a perovskite-based photodetector can be increased by as much as 250% by layering the material onto a metallic substrate rather than one made of glass, reports a research team based in the United States and China (Nat. Photon., doi: 10.1038/s41566-022-01151-3). The dramatic boost in efficiency, according to the team, suggests that cheap and abundant perovskites could replace silicon in photonic devices such as solar cells, for which the cost of mining and purifying raw silica remains a barrier to mass-market adoption.
Slashing recombination rate
The optical and electronic properties of lead-halide perovskites make them an appealing option for photonic devices, but complex chemical treatments are typically needed to achieve the long carrier lifetimes needed for efficient solar cells and detectors. In the latest study, however, a research team led by Chunlei Guo at the University of Rochester, USA, found that spin-coating a thin layer of perovskite material onto a metallic substrate, or one made of a metamaterial containing alternating layers of metal and dielectric material, can dramatically suppress the recombination processes that kill carrier lifetimes.
“Putting a metal platform under a perovskite utterly changes the interaction of the electrons within the perovskite,” comments Guo. “As new perovskites emerge, we can use our physics-based method to further enhance their performance.”
For one of the most studied perovskites, MAPbI3, the researchers found that the recombination rate was reduced by 30% when layered directly onto a metamaterial, and by 50% for a substrate containing a single layer of silver. Even more striking results were achieved for a more complex triple-cation perovskite that contains some cesium, a material that has recently captured attention for its enhanced stability and reproducible performance. When this perovskite was spin-coated onto a plasmonic substrate, the researchers recorded a 10-fold reduction in the rate of recombination.
Surprising results
The team expected to see some improvement in carrier lifetimes: mirror images of electron–hole pairs in the perovskite are generated in the plasmonic substrates, weakening the ability of electrons to recombine with the holes. But Guo and his colleagues were surprised by the scale of the response in the triple-cation perovskite, which also showed a six-fold reduction in the recombination rate when layered onto a metamaterial.
Citing “a lot of surprising physics,” the team suggests that the plasmonic and metamaterial platforms enable excited electrons to be released from shallow trapped states in the perovskite, which, in addition to the mirror-image effect, further prolongs the carrier lifetime.