Thin solar cell turns any surface into a power source

MIT engineers have developed a method of fabricating thin and light solar cells that can be added to any surface.

The cells that result from the new technique are durable and flexible. When glued to a strong, lightweight fabric, the cells provide an energy source which can be rapidly deployed. They are 1% of the weight of conventional solar panels, while generating 18 times more power-per-kilogram. The cells are made from semiconducting inks using printing processes that can be scaled in the future to large-area manufacturing. Being thin and lightweight, the solar cells can be laminated onto many different surfaces 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. Just as important is integrability — the ease with which the new technology can be adapted. The lightweight solar fabrics enable integrability, providing impetus for the current work. We strive to accelerate solar adoption, given the present urgent need to deploy new carbon-free sources of energy,” says Vladimir Bulović, the Fariborz Maseeh Chair in Emerging Technology, leader of the Organic and Nanostructured Electronics Laboratory (ONE Lab), director of MIT.nano, and senior author of a new paper describing the work. Co-lead authors on the paper are Mayuran Saravanapavanantham, an electrical engineering and computer science graduate student at MIT; and Jeremiah Mwaura, a research scientist in the MIT Research Laboratory of Electronics.

Six years ago, the ONE Lab team produced solar cells using an emerging class of thin-film materials that were so lightweight they could sit on top of a soap bubble. But these ultrathin solar cells were fabricated using complex, vacuum-based processes, which can be expensive and challenging to scale up. They then set out to develop thin-film solar cells that are printable using ink-based materials and scalable fabrication techniques.

The new solar cells are made from nanomaterials in the form of a printable electronic inks. In the MIT.nano clean room, the researchers coated the solar cell structure using a slot-die coater, which deposits layers of the electronic materials onto a substrate that is only 3 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 in thickness, off the plastic substrate, forming an ultralight solar device. That solar device is fragile, and can easily tear. To solve this challenge, the MIT team searched for a lightweight, flexible, and high-strength substrate for the solar cells. Fabrics were the optimal solution, as they provide mechanical resilience and flexibility with little added weight. The ideal material they found was a composite fabric that weighs only 13 grams per square meter, commercially known as Dyneema. By adding a few microns thick layer of UV-curable glue, the solar modules are adhered to the fabric.

Testing the device, the MIT researchers found it could generate 730 watts of power per kilogram when freestanding and about 370 watts-per-kilogram if deployed on the Dyneema fabric, which is about 18 times more power-per-kilogram than conventional solar cells. They also tested the durability of their devices and found that, even after rolling and unrolling a fabric solar panel more than 500 times, the cells still retained more than 90 percent of their initial power generation capabilities. The solar cells would still need to be encased in another material to protect them from the environment as the carbon-based organic material used to make the cells could be modified by interacting with moisture and oxygen in the air, deteriorating their performance.

This research is funded, in part, by Eni S.p.A. through the MIT Energy Initiative, the U.S. National Science Foundation, and the Natural Sciences and Engineering Research Council of Canada. The research was published in Small Methods.