Perovskites change shape when exposed to light

　　Perovskite crystals can change shape in response to light according to researchers at King Abdullah University of Science and Technology.They believe the crystals could form the heart of novel light-activated devices.

　　Photostriction is the property of certain materials to undergo a change in internal strain,and therefore shape,with exposure to light.Organic photostrictive materials are said to offer the greatest shape change in response to light–a parameter known as the photostrictive coefficient–but their response is slow and unstable under ambient conditions.

　　While searching for photostriction in new materials,the researchers found that the perovskite called MAPbBr3 revealed strong and robust photostriction behaviour.

　　To extensively test the material’s photostriction capabilities,the team developed a new method using Raman spectroscopy,which probes the molecular vibrations within the structure.When bathed in light,photostriction alters the internal strain in the material,which then shifts the internal pattern of vibrations.By measuring the shift in the Raman signal when the material was placed under mechanical pressure,the team could calibrate the technique and use it to quantify the effect of photostriction.

　　“We demonstrated that in situ Raman spectroscopy with confocal microscopy is a powerful characterisation tool for measuring intrinsic photoinduced lattice deformation,”says electrical engineer Tzu-Chiao Wei.

　　According to the researchers,the perovskite material possesses a significant photostriction coefficient of 1.25%.The spontaneous generation of positive and negative charges when the perovskite is bathed in light polarises the material,which induces a movement in the ions in the material.

　　“We could use this material to fabricate next-generation optoelectronic devices,including wireless remote switchable devices and other light-controlled applications,”Wei concludes.