npj Flexible Electronics<\/a>.<\/p>\n\u201cIf it\u2019s cracked, it compromises the mechanical integrity of the entire device. This is the first clear evidence of cracking in a device substrate caused by a brittle film on top of it.\u201d<\/p>\n
The layers used in flexible electronics have specific jobs. The top layer conducts electricity across the surface to keep the device running. That layer is usually made of special ceramic oxide materials because they are transparent and also good conductors, which is essential for things like display screens, sensors, and solar cells. But ceramics are brittle and prone to cracking, so the substrate\u2019s job is to add some toughness. Substrates are generally made from polymer materials that are highly flexible and resist cracking.<\/p>\n
While using these materials to make flexible solar cells, Anush Ranka, a postdoctoral researcher at Brown who performed the work as a PhD student in materials science, became increasingly curious about the mechanism by which fatigue can degrade performance. He decided to take a closer look at the cracking processes.<\/p>\n
For the study, Ranka made small experimental devices using various types of ceramic electrodes and polymer substrates. He then subjected them to bending tests and used a powerful electron microscope to examine the cracks. In places where he found cracks in the ceramic layer, he used a focused ion beam\u2014a kind of nanoscale sandblaster\u2014to etch away the ceramic and reveal the substrate directly beneath a ceramic crack.<\/p>\n
The work showed that cracks in the ceramic layer often drive deeper cracks into the substrate. The effect occurred across ceramic and polymer combinations, suggesting this is a common\u2014and surprising\u2014failure mechanism in flexible electronics. Once cracks form deep in the polymer, the researchers say, they become permanent structural defects. With repeated bending, these cracks widen, misalign, or fill with debris, which then prevents the ceramic crack faces from reconnecting. That causes electrical resistance to increase and device performance to degrade.<\/p>\n
Working with Haneesh Kesari, a Brown engineering professor who specializes in theoretical and applied mechanics, and solid mechanics PhD student Sayaka Kochiyama, the researchers analyzed this cracking problem. They showed that a mismatch in the elastic properties of the two layers was driving the deep cracking phenomenon in the substrate. Understanding the cracking mechanism led the team toward a potential fix: Adding a third layer of material between the ceramic and the substrate that mitigates the elastic mismatch.<\/p>\n
\u201cWe created a design map that identified hundreds of polymers that, with the correct thickness, could potentially mitigate this elastic mismatch and prevent cracking in a wide range of electrode-substrate combinations,\u201d says Padture who leads Brown\u2019s Initiative for Sustainable Energy.<\/p>\n
\u201cUsing this design map, we were able to choose a specific polymer for the third layer and experimentally demonstrate the feasibility of our approach.\u201d<\/p>\n
The researchers are hopeful that the design diagram will make for more durable devices. Just as important, however, is the discovery that cracks do indeed affect polymer substrates\u2014a fact that was not apparent before this research.<\/p>\n
\u201cWe\u2019re essentially solving a problem people didn\u2019t know they had,\u201d Padture says. \u201cWe think this could significantly improve the cyclic life of flexible devices.\u201d<\/p>\n
Other researchers from Brown, Yale University, and University of Rome Tor Vergata also contributed to the work.<\/p>\n
Support for the research came from the US Department of Energy, the US National Science Foundation, and the Office of Naval Research.<\/p>\n
Source: Brown University<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"Share this Article You are free to share this article under the Attribution 4.0 International license. Researchers have…\n","protected":false},"author":2,"featured_media":63848,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[4087,61,60,43791,80],"class_list":{"0":"post-63847","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-technology","8":"tag-electronics","9":"tag-ie","10":"tag-ireland","11":"tag-mobile-devices","12":"tag-technology"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/63847","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/comments?post=63847"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/63847\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media\/63848"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media?parent=63847"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/categories?post=63847"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/tags?post=63847"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}