Cooling through solid-state electrocaloric materials is an attractive replacement for vapor compression. Despite recent efforts, devices that are potentially commercially competitive have not been developed. We present an electrocaloric cooler with a maximum temperature span of 20.9 kelvin and a maximum cooling power of 2.1 watts under the moderate applied electric field of 10 volts per micrometer without any observed breakdown. Moreover, the maximum coefficient of performance, even taking into account energy expended on fluid pumping, reaches 54% of Carnot’s efficiency as long as energy is properly recovered. We believe that this demonstration shows electrocaloric cooling to be a very promising alternative to vapor compression cooling.

Coming up with sustainable sources of electricity is one of the grand challenges of this century. The research field of materials for energy harvesting stems from this motivation, including thermoelectrics¹, photovoltaics² and thermophotovoltaics³. Pyroelectric materials, converting temperature periodic variations in electricity, have been considered as sensors⁴ and energy harvesters^5–7, although we lack materials and devices able to harvest in the joule range. Here we develop a macroscopic thermal energy harvester made of 42 g of lead scandium tantalate in the form of multilayer capacitors that produces 11.2 J of electricity per thermodynamic cycle. Each pyroelectric module can generate up to 4.43 J cm⁻³ of electric energy density per cycle. We also show that two of these modules weighing 0.3 g are sufficient to sustainably supply an autonomous energy harvester embedding microcontrollers and temperature sensors. Finally, we show that for a 10 K temperature span these multilayer capacitors can reach 40% of Carnot efficiency. These performances stem from (1) a ferroelectric phase transition enabling large efficiency, (2) low leakage current preventing losses and (3) high breakdown voltage. These macroscopic, scalable and highly efficient pyroelectric energy harvesters enable the reconsideration of the production of electricity from heat.

As a major challenge, sustainable energy management and energy self-sufficiency require microsystems that manage multiple energy operations in a single device. In this work, flexible thick-film structures with promising energy storage and electrocaloric cooling capabilities as well as piezoelectric properties are developed. The functional thick-film layer is based on relaxor-ferroelectric 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–35PT) directly deposited on a flexible polyimide substrate by an aerosol deposition method. The thick-film structures exhibit a promising recoverable energy-storage density of 10.3 J cm⁻³. After extensive bending tests, the structures showed no signs of degradation. The high bendability and durability are confirmed by stable energy storage properties after bending up to a radius of 1.5 mm (2.4% bending strain) and 10⁵ repeated bending cycles. The developed thick-film structures also exhibit a piezoelectric coefficient d₃₃ of ∼80 pm V⁻¹. Using two direct electrocaloric measurement methods, we demonstrated that the electrocaloric temperature change in the prepared PMN–35PT thick-film structures reaches a maximum of 0.87 K at 63.5 °C and 300 kV cm⁻¹, which exceeds the value of 0.72 K at ∼65 °C and 60 kV cm⁻¹ reported for bulk ceramics of the same composition. The PMN–35PT thick films prepared here are thick-film structures with excellent flexibility, promising for future multifunctional microsystems that manage multiple energy operations, enabling comprehensive energy harvesting, storage and conversion to thermal energy.

Reliable and accurate characterization of the electrocaloric effect is necessary to understand the intrinsic properties of materials. To date, several methods are developed to directly measure the electrocaloric effect. However, each of them has some limitations, making them less suitable for characterizing ceramic films, which rely almost exclusively on less accurate indirect methods. Here, a new approach is proposed to address the process of rapid heat dissipation in ceramic films and to detect the electrically induced temperature change before it thermally bonds with the surrounding elements. By using a polymer substrate that slows heat dissipation to the substrate and fast infrared imaging, a substantial part of the adiabatic electrocaloric effect in Pb(Mg_1/3Nb_2/3)O₃‐based ceramic films is captured. Infrared imaging provides a robust technique to reduce the ratio between the adiabatic and the measured electrocaloric temperature change in micrometer‐sized ceramic films to a single‐digit number, ≈3.5. The obtained results are validated with another direct thermometric method and compared with the results obtained with an indirect approach. Despite different measurement principles, the results obtained with the two direct methods agree well. The proposed approach is timely and can open a door to verify the predicted giant electrocaloric effects in ceramic films.