Energy Focus: Large grain size may improve efficiency of perovskite solar cells

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electronic foil is transferred onto a pre-stretched elastomer (left, middle) forming out-of-plane wrinkles upon release (right). Reprinted with permission from Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. © 2014.

while continuously recording the resistance. All the metal conductors where cycled up to 1000 times (Ag, Au, and Cu) or until failure (Al, ca. 400 times); the conducting polymer PEDOT:PSS was fatigued up to 10,000 cycles. Au, Cu, and PEDOT:PSS were found to be highly reliable, withstanding 1000 stretch cycles for the metals, and 10,000 for the polymer conductor without failure. In addition, the resistance slightly increased by 30% over the course of 10,000 cycles. However, the researchers found no indication of fracture of the PEDOT:PSS. The resistance increase may be attributed to the operation in ambient air and the potential water uptake during fatigue. “The main advantage of our approach is the planar fabrication of our stretchable interconnects and the easy transfer on mechanically stretchable substrates,” says Drack. This work “is just a first step toward a novel technology platform with the thinnest and most flexible circuit boards,” he says. Such highly reliable transparent electrodes form the basis of new avenues for the design of complex, hybrid rigid-island stretchable-interconnect electronic devices such as light-emitting diode strips that can be stretched and twisted without impairing their function. Such materials are in demand in applications in textiles, wearable as glasses, and inner organs like hearts where flexibility, compliance, weight, and softness are important to next-generation electronic devices. Jean L. Njoroge

Perovskite photovoltaics are organic–inorganic hybrids such as CH 3 NH 3 PbX 3 —where X is a halide—that are in the perovskite crystal phase. They are more attractive than the conventional silicon-based solar cells due to their cost-effective fabrication and high power-conversion efficiency. However, they have issues of stability and reproducibility and exhibit persistent hysteresis during device operation. Therefore, the article published

in the January 30 issue of Science (DOI: 10.1126/science.aaa0472; p. 522), by lead authors Aditya Mohite and Hsing-Lin Wang and colleagues at LANL, represents a significant development in moving toward cheap, commercially viable perovskite photovoltaics. To create a uniform perovskite film, an equimolar solution of PbI2 and methylamine hydrochloride were dissolved in a high-boiling-point solvent such as N,N-dimethylformamide (DMF), heated

Energy Focus Design of imperceptible plastic electronics make flexible electronic devices promising

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he inside of a computer or a mobile phone contains a stiff circuit board that is green in color, is crammed with chips, resistors, capacitors, and sockets, and is interconnected by a suburban sprawl of printed wiring. What if the circuit board was not rigid, but flexible enough to fold? Now, Michael Drack of Johannes Kepler University in Austria, T. Sekitani of the University of Tokyo and their collea