A race is on in solar engineering to create almost impossibly-thin, flexible solar panels. Engineers imagine them used in mobile applications, from self-powered wearable devices and sensors to lightweight aircraft and electric vehicles. Against that backdrop, researchers at Stanford University have achieved record efficiencies in a promising group of photovoltaic materials. Chief among the benefits of these transition metal dichalcogenides – or TMDs – is that they absorb ultrahigh levels of the sunlight that strikes their surface compared to other solar materials.

Transition metal dichalcogenide solar cells on a flexible polyimide substrate

“Imagine an autonomous drone that powers itself with a solar array atop its wing that is 15 times thinner than a piece of paper,” said Koosha Nassiri Nazif, a doctoral scholar in electrical engineering at Stanford and co-lead author of a study published in the Dec. 9 edition of Nature Communications. “That is the promise of TMDs.”

The search for new materials is necessary because the reigning king of solar materials, silicon, is much too heavy, bulky and rigid for applications where flexibility, lightweight and high power are preeminent, such as wearable devices and sensors or aerospace and electric vehicles.

“Silicon makes up 95 percent of the solar market today, but it’s far from perfect. We need new materials that are light, bendable and, frankly, more eco-friendly,” said Krishna Saraswat, a professor of electrical engineering and senior author of the paper. While TMDs hold great promise, research experiments to date have struggled to turn more than 2 percent of the sunlight they absorb into electricity. For silicon solar panels, that number is closing in on 30 percent. To be used widely, TMDs will have to close that gap.

The new Stanford prototype achieves 5.1 percent power conversion efficiency, but the authors project they could practically reach 27 percent efficiency upon optical and electrical optimizations. That figure would be on par with the best solar panels on the market today, silicon included.

Moreover, the prototype realized a 100-times greater power-to-weight ratio of any TMDs yet developed. That ratio is important for mobile applications, like drones, electric vehicles and the ability to charge expeditionary equipment on the move. When looking at the specific power – a measure of electrical power output per unit weight of the solar cell – the prototype produced 4.4 watts per gram, a figure competitive with other current-day thin-film solar cells, including other experimental prototypes. “We think we can increase this crucial ratio another ten times through optimization,” Saraswat said, adding that they estimate the practical limit of their TMD cells to be a remarkable 46 watts per gram.”

Source: https://news.stanford.edu/

Tesla has unveiled its latest structural battery pack with 4680 cells during a Gigafactory Berlin tour ahead of Model Y production at the new factory. The start of production at Gigafactory Berlin is not just significant for Tesla’s growth in Europe, but it will also mark the launch of an important new version of the Model Y. Tesla plans to build the new Model Y at Gigafactory Berlin on a whole new platform with its structural battery pack.

At its Battery Day event last year, Tesla not only unveiled its new 4680 battery cell but also a new battery architecture built around the new cell. Inspired by the aerospace innovation of building airplane wings as fuel tanks instead of building the fuel tanks inside the wings, Tesla decided to build a battery pack that acts as a body structure, linking the front and rear underbody parts. Currently, Tesla builds battery packs by combining cells into modules, which are put together to form a battery pack. That battery pack is installed into the vehicle platform.

The difference with this new concept is that Tesla is not using modules, and is instead building the entire battery pack as the structural platform of the vehicle, with the battery cells helping to solidify the platform as one big unit. Using its expertise in giant casting parts, Tesla can connect a big single-piece rear and front underbody to this structural battery pack.

This new design reduces the number of parts, the total mass of the battery pack, and therefore enables Tesla to improve efficiency and ultimately the range of its electric vehicles (412 Miles or 663 km).

Source: https://electrek.co/

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure. Now, a team of Penn Engineers has demonstrated a new material they call “nanocardboard,” an ultrathin equivalent of corrugated paper cardboard. A square centimeter of nanocardboard weighs less than a thousandth of a gram and can spring back into shape after being bent in half.

Nanocardboard is made out of an aluminum oxide film with a thickness of tens of nanometers, forming a hollow plate with a height of tens of microns. Its sandwich structure, similar to that of corrugated cardboard, makes it more than ten thousand times as stiff as a solid plate of the same mass.

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Nanocardboard is made out of an aluminum oxide film with a thickness of tens of nanometers, forming a hollow plate with a height of tens of microns. Its sandwich structure, similar to that of corrugated cardboard, makes it more than ten thousand times as stiff as a solid plate of the same mass. A square centimeter of nanocardboard weighs less than a thousandth of a gram and can spring back into shape after being bent in half.

Nanocardboard‘s stiffness-to-weight ratio makes it ideal for aerospace and microrobotic applications, where every gram counts. In addition to unprecedented mechanical properties, nanocardboard is a supreme thermal insulator, as it mostly consists of empty space. Future work will explore an intriguing phenomenon that results from a combination of properties: shining a light on a piece of nanocardboard allows it to levitate. Heat from the light creates a difference in temperatures between the two sides of the plate, which pushes a current of air molecules out through the bottom.

Igor Bargatin, Assistant Professor of Mechanical Engineering, along with lab members Chen Lin and Samuel Nicaise, led the study.

They published their results in the journal Nature Communications.

Source: https://phys.org/