A team of engineers at MIT has developed ultralight fabric solar cells that can quickly and easily turn any surface into a power source.
The durable, flexible solar cells, which are much thinner than a human hair, are glued to a strong, lightweight fabric, making them easy to install on a fixed surface. They can provide energy on the go as a wearable power fabric or be transported and rapidly deployed in remote locations for assistance in emergencies. They are one-hundredth the weight of conventional solar panels, generate 18 times more power-per-kilogram and are made from semiconducting inks using printing processes that can be scaled in the future to large-area manufacturing.
Because they are so thin and lightweight, the solar cells can be laminated onto many different surfaces. For instance, they could be integrated onto the sails of a boat to provide power while at sea, adhered onto tents and tarps that are deployed in disaster-recovery operations, or applied to the wings of drones to extend their flying range. The lightweight solar technology can also be easily integrated into built environments with minimal installation needs.
‘The metrics used to evaluate a new solar cell technology are typically limited to their power-conversion efficiency and their cost in dollars-per-watt,’ said Vladimir Bulović, the Fariborz Maseeh chair in emerging technology at MIT. ‘Just as important is integrability – the ease with which the new technology can be adapted.’
Traditional silicon solar cells are fragile, so they must be encased in glass and packaged in thick, heavy aluminium framing, which limits where and how they can be deployed.
Six years ago, the MIT team produced solar cells using an emerging class of thin-film materials that were so lightweight that they could sit on top of a soap bubble. However, these ultrathin solar cells were fabricated using complex, vacuum-based processes, which can be expensive and challenging to scale up.
In the present work, they set out to develop thin-film solar cells that are entirely printable, using ink-based materials and scalable fabrication techniques. To produce the solar cells, they use nanomaterials that are in the form of a printable electronic inks. Working in the MIT.nano clean room, they coat the solar cell structure using a slot-die coater, which deposits layers of the electronic materials onto a prepared, releasable substrate that is only three microns thick. Using screen printing, an electrode is deposited on the structure to complete the solar module.
The researchers can then peel the printed module, which is about 15 microns thick, off the plastic substrate, forming an ultralight solar device. However, such thin, freestanding solar modules are challenging to handle and can easily tear, which would make them difficult to deploy. To solve this challenge, the MIT team searched for a lightweight, flexible and high-strength substrate to which they could adhere the solar cells. They identified fabrics as the optimal solution, as they provide mechanical resilience and flexibility with little added weight.
The ideal material proved to be a composite fabric that weighs only 13 grams per square metre, commercially known as Dyneema. The fabric is made of fibres that are so strong that they were used as ropes to right the stricken cruise ship Costa Concordia. By adding a layer of UV-curable glue, which is only a few microns thick, they adhere the solar modules to sheets of this fabric to form an ultra-light and mechanically robust solar structure.
‘While it might appear simpler to just print the solar cells directly on the fabric, this would limit the selection of possible fabrics or other receiving surfaces to the ones that are chemically and thermally compatible with all the processing steps needed to make the devices. Our approach decouples the solar cell manufacturing from its final integration,’ explained Mayuran Saravanapavanantham, an electrical engineering and computer science graduate student.
When they tested the device, the researchers found that it could generate 730 watts of power per kilogram when freestanding and about 370 watts per kilogram if deployed on the high-strength Dyneema fabric, which is about 18 times more power per kilogram than conventional solar cells.
‘A typical rooftop solar installation in Massachusetts is about 8,000 watts. To generate that same amount of power, our fabric photovoltaics would only add about 20 kilograms to the roof of a house,’ Saravanapavanantham said.
The team also tested the durability of the devices and found that, even after rolling and unrolling a fabric solar panel more than 500 times, the cells still retained more than 90 per cent of their initial power-generation capabilities.
While the solar cells are much lighter and more flexible than traditional cells, they would need to be encased in another material to protect them from the environment. The carbon-based organic material used to make the cells could be modified by interactions with moisture and oxygen in the air, which could cause their performance to deteriorate.
‘Encasing these solar cells in heavy glass, as is standard with the traditional silicon solar cells, would minimise the value of the present advancement, so the team is currently developing ultrathin packaging solutions that would only fractionally increase the weight of the present ultralight devices,’ said Jeremiah Mwaura, a research scientist in the MIT Research Laboratory of Electronics.
The research has been published in Small Methods.