Waste heat generated by electronics is a big problem. Not only can it damage components if it gets out of hand, but it represents a large amount of energy going to waste. Now scientists at the University of California, Berkeley have developed a thin film that could be built into computers, cars or factories to capture and recycle the energy from waste heat.

Many existing systems that tap into this energy source work on the thermoelectric principle, which generates electricity through the temperature difference between two sides of a material. That works well for devices like the JikoPower, which captures heat from pots and pans while cooking to charge phones, but it's not much use for smaller temperature differences between the hot and cold sides of a material.

The UC Berkeley team wanted to create a device that could tap into what's known as low-quality waste heat, which involves temperatures below 100° C (212° F). To do so, the new film works on the principle of pyroelectric energy conversion, which can work with lower temperatures and more gradual changes. That makes it ideal for use in electronics.

"We know we need new energy sources, but we also need to do better at utilizing the energy we already have," says Lane Martin, senior author of the study. "These thin films can help us squeeze more energy than we do today out of every source of energy."

The team built prototype devices that supplied heat and electric fields to pyroelectric films just 50 to 100 nanometers thick, and measured the temperature and amount of electricity they generated. The devices managed to achieve an energy density of 1.06 Joules per cm3, a power density of 526 W per cm3, and a Carnot efficiency of 19 percent. According to the team, all of these figures are new records for this kind of pyroelectric energy conversion.

The researchers say their work helps improve our understanding of pyroelectric physics, which in turn can improve how these devices are designed. In future, the films could be optimized for individual systems, depending on how much heat is being lost and at what temperature.

"Part of what we're trying to do is create a protocol that allows us to push the extremes of pyroelectric materials so that you can give me a waste-heat stream and I can get you a material optimized to address your problems," says Martin.

The research was published in the journal Nature Materials.