Defect engineering increases polarization retention in ferroelectric thin films
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esearchers report a new strategy to make high-quality perovskite quantum dots (QDs), giving QD solar cells with a record certified power-conversion efficiency of 16.6%. Perovskite QD solar cells could be more stable than their thin-film counterparts, but making highquality QDs with desirable optoelectronic properties has been a challenge. “This substantial improvement of efficiency and stability paves the way for addressing high-value applications in
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nfrared (IR) light-emitting diodes (LEDs) used in night vision, optical communications, and medical applications are expensive. Embedding lead sulfide QDs into perovskite films could give low-cost, efficient IR LEDs. These devices combine the tunability of QDs to precise wavelength emissions with excellent charge-transport properties of perovskites. But the QDs
niche markets,” says Yang Bai of The University of Queensland in Australia and an author of the Nature Energy paper (doi:10.1038/s41560-019-0535-7). Bai and colleagues made cesium and formamidinium lead triiodide perovskites (Cs1–xFAxPbI3) QDs by first preparing CsPbI3 and FAPbI3 QDs using a modified hot-injection method. Before mixing them together, they intentionally retained excessive oleic acid (OA) ligands in the parent CsPbI3 and FAPbI3
QD solutions, forming an OA-rich environment. The surface ligands promoted a cation exchange reaction of the Cs and FA cation and suppressed surface defects, boosting efficiency. The best material, Cs0.5FA0.5PbI3, gave solar cells a remarkable power-conversion efficiency of 16.6% and negligible hysteresis. The cell retained 94% of its efficiency under continuous 1-Sun illumination for 600 hours, a stability comparable to that of thin-film materials.
tend to aggregate, causing inhomogeneity because of imbalanced charge accumulation. To overcome these issues, a team led by Jiang Tang of the Huazhong University of Science & Technology and Edward Sargent of the University of Toronto turned to low-dimension layered perovskites as a matrix for QDs. They altered the surface of the QDs with
perovskite cations, which caused them to disperse evenly through the matrix. In the LEDs reported in Nature Photonics (doi:10.1038/s41566-019-0577-1), energy flowed in the form of excitons, tightly bound electron–hole pairs that traveled together, from the perovskite into the QDs. The devices exhibited a high external quantum efficiency of 8.1% at 980 nm at a radiance of up to 7.4 W Sr−1m−2.
Nano Focus Defect engineering increases polarization retention in ferroelectric thin films
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erroelectric thin films are intriguing candidates for nanoscale electronics, including memory systems in which information is stored as polarization states equivalent to the 1s and 0s of binary systems. Researchers at the University of New South Wales (UNSW) and Monash University in Australia have recently overcome a key limitation of this technology—the decay of polarization states over short time scales. As they described in Nature Communications (doi:10.1038/ s41467-019-14250-7), they utilized de
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