Developing sustainable electricity sources remains a critical challenge of this century. Pyroelectric materials offer a promising approach for transforming waste heat into electric power. However, their practical application has been constrained by very low power outputs, typically ranging from microwatts to milli-watts. Here we present a macroscopic pyroelectric generator that continuously delivers 1 W of electric power by running an Olsen cycle with 4.3 cm3 of active pyroelectric material. Moreover, the maximum power density of our generator reaches 400 W per liter of active materials. We also demonstrate an autonomous system exclusively powered by a pyroelectric generator following a Stirling cycle. This advancement underscores the potential of nonlinear pyroelectric generators as a highly competitive technology for harvesting low-grade waste energy.

Pyroelectric materials are attractive for converting heat into electricity, yet the best performance is obtained with lead-containing ceramics, remaining a major environmental concern. Here, we address this problem by developing lead-free barium strontium titanate multilayer capacitors (Ba0.65Sr0.35Ti0.998Mn0.002O3 MLCs). A maximum energy density of 3.7 J cm-3 is achieved under an applied field of 300 kV cm-1 across a 170 K temperature span in an Olsen electro-thermodynamic cycle. We conducted Olsen cycles with two approaches: electric displacement-electric field (D-E) loops and stepwise control of temperatures and voltages, which provide consistent results. In addition, we found that Ba0.65Sr0.35Ti0.998Mn0.002O3 MLCs show a second-order ferroelectric-to-paraelectric (FE-to-PE) phase transition, which shifts to higher temperatures by the applied electric field. This provides a broad and practical temperature window for low-grade waste heat recovery. Our study shows that the performance of pyroelectric energy harvesting in barium strontium titanate materials is comparable to their conventional lead-based counterpart (3.6 J cm-3 in lead scandium tantalate in similar conditions), revealing the promising prospects of sustainable energy recovery applications.

Abstract State-of-the-art electrocaloric cooling prototypes rely on the conventional electrocaloric effect of ferroelectric lead scandium tantalate (PbSc0.5Ta0.5O3, PST), which peaks near room temperature. Here, we demonstrate that A-site calcium doping in highly ordered PST modifies its phase transitions and enables precise tuning of the electrocaloric response. The transition temperature shifts down to 258 K and up to 319 K, depending on Ca concentration. Calorimetry under electric field, electrical polarization loops, and piezoresponse force microscopy reveal the emergence of an intermediate antiferroelectric phase stabilized for Ca ≥ 2%. These results are supported by first-principles calculations. We observe conventional electrocaloric effect for Ca ≤ 2% and inverse electrocaloric effect at higher doping (≥ 2%). Under an applied field of 110 kV cm−1, Ca-doped PST exhibits an adiabatic temperature change of 2 K over a range from 263 K to 353 K. Such Ca-doped PST compounds could be used to expand the temperature range of PST below the freezing point of water. Our results offer a pathway to cascaded electrocaloric cooling devices with extended operating spans.

K0.5Na0.5NbO3 is among the most promising lead-free piezoelectrics. While its sputtered films match the performance of the champion piezoelectric Pb(Zr,Ti)O3, reproducible processing of high-quality and time-stable solution-deposited K0.5Na0.5NbO3 films remains challenging. Here, we report 1 mu m-thick Mn-doped K0.5Na0.5NbO3 films prepared via a chemical solution deposition process, which have perfectly dense microstructure and uniform composition across their thickness. The films exhibit a high transverse piezoelectric coefficient (e31,f = -15.4 C/m2), high dielectric permittivity (epsilon r approximate to 920), low dielectric losses (tans = 0.05) and can withstand electric fields up to at least 1 MV/cm. Their functional properties show excellent stability over time, and the synthesis process is reproducible. Furthermore, a surface acoustic haptic device based on K0.5Na0.5NbO3 thin-film actuators is demonstrated. The results validate the high potential of Mn-doped K0.5Na0.5NbO3 films to replace lead-based Pb(Zr,Ti)O3 films in piezoelectric applications.

Lead zirconate (PbZrO3) stands out as the prototypical antiferroelectric material, often studied for its applications in link capacitors and actuators. However, the conventional fabrication of single crystal films necessitates costly vacuum techniques and face scalability challenges. Exploiting scalable solution-based methods could unlock their full potential at reduced costs. Here, a chemical route for the preparation of high-quality single-crystal PbZrO3 thin films on Nb-doped SrTiO3 substrates is presented. Films with different thicknesses were grown and their structure was characterized by X-ray diffraction and transmission electron microscopy. Metal-insulator-metal capacitors were built to study their electrical switching characteristics. An unexpected ferroelectric-like switching is observed in 170 nm-thick film, while antiferroelectric-like switching is observed in 680 nm-thick films. The presence of ferroelectric-like switching is associated with the defect formation during the high-temperature annealing of the films.

Since the discovery of ferroelectricity in HfO2 thin films, significant research has focused on Zr-doped HfO2 and solid-solution (Hf,Zr)O2 thin films. Functional properties can be further tuned via multilayering; however, this approach has not yet been fully explored in HfO2-ZrO2 films. This work demonstrates ferroelectricity in a 50 nm-thick, solution-processed HfO2-ZrO2 multilayer film, marking it as the thickest multilayer film to date exhibiting ferroelectric properties. The multilayer structure was confirmed through transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy, with high-resolution TEM revealing grain continuity across multiple layers. This finding indicates that a polar phase in the originally paraelectric ZrO2 layer can be stabilized by the HfO2 layer. The film attains a remanent polarization of 9 μC cm-2 and exhibits an accelerated wake-up behavior, attributed to its higher breakdown strength, resulting from the incorporation of multiple interfaces. These results offer a faster wake-up mechanism for thick ferroelectric hafnia films.

Thermal energy conversion using non-linear pyroelectric materials present a sustainable solution for transforming waste heat into useful energy. By utilizing the temperature and electric field dependence of these materials, heat can be directly converted into electrical energy. This review explores non-linear pyroelectric energy conversion, highlighting the use of ferroelectric materials and their non-linear behaviour in thermal energy harvesting. In this work, we critically examine the materials, thermodynamic cycles for pyroelectric energy conversion, figures-of-merit for pyroelectric energy harvesting, and the influence of material geometry, aging and conversion losses. The primary objective of this review is to emphasize the importance of power generation through pyroelectric modules and re-examine the scope of macroscopic pyroelectric energy harvesters for practical applications. Concepts related to macroscopic devices such as regeneration and heat exchange conditions using thermal control elements for thermal energy harvesting are also discussed. This article aims to provide a comprehensive overview of the advancements, challenges, and future directions in the field of non-linear pyroelectric energy harvesting.

In this study, we present a lead-free, piezoelectric energy harvester capable of generating power in the milliwatt range. The harvester consists of four layers of polyvinylidene difluoride piezoelectric polymer, bonded to a cantilever with a tip mass. The cantilever’s resonance frequency was measured at 13.4 Hz. The piezoelectric layers are connected in parallel, resulting in a total capacitance of 27 nF. At resonance, under open-circuit conditions, the harvester generates nearly 90 Vpp when subjected to an acceleration of 1 g. When impedance is matched, the maximum power output reaches 2.4 mW. In addition, we integrated the harvester with commercially available signal conditioning cards, enabling conversion from an AC signal to a steady 3.3 V DC signal useful for electronics to evaluate their efficiency in charging a capacitor. Finally, we demonstrated the harvester’s functionality in an autonomous system that measures and displays temperature on a digital screen. The system operated autonomously for 6.5 h.

In a recent issue of Device, Zhang et al. describe an elastocaloric cooling system with two essential new features: a cam-driven mechanism reducing the overall size of the system and NiTi elastocaloric tubes with fin inner structures enabling a much better heat exchange.

The demand for flexible, low-cost, and lightweight sensors is increasing, particularly for structural health monitoring in harsh environments exposed to temperature fluctuations and mechanical strain. Inkjet printing, an additive manufacturing technique for electronics, offers low-cost fabrication with high spatial resolution. In this work, we present strain sensors fabricated by inkjet-printing silver onto flexible Kapton substrates. The sensing grid is protected from the environment by a polymeric encapsulant. The sensors exhibit a linear increase in resistance with increasing strain, with gauge factor values ranging from 1.40 to 1.80 recorded over a temperature range of −40 to 100 °C. Furthermore, we demonstrate the applicability of these sensors for monitoring the mechanical deformation of a propellant tank with an aluminum liner. The strain sensor was printed directly onto the Kapton, which was pre-glued on a curved surface (tank). To compensate for temperature effects, two strain gauges, i.e., one aligned in the hoop direction and the other in the axial direction, were connected in a half-Wheatstone bridge configuration. A linear increase in output voltage with rising internal pressure up to 50 bar was observed, confirming the potential of inkjet-printed sensors for direct integration into structural health monitoring systems.

The functionalization of thin, flexible glass with piezoelectric oxides is a pathway toward transparent electromechanical devices. The crystallization of lead zirconate titanate thin films on thick, rigid glass is previously demonstrated using flash lamp annealing to selectively anneal the films, without damaging the substrates. In this work, a 2‐step process suitable for Schott AF 32 eco glass and Corning Willow glass is developed, both 100 μm thick, the latter of which is compatible with roll‐to‐roll processes. Herein, demonstration is done of: 1) the importance of heat management during flash lamp annealing; and 2) a method to orient perovskite thin films during their crystallization by flash lamp annealing. With this process, the 540 nm thick lead zirconate titanate thin films with morphotropic phase boundary composition display a relative permittivity ε r of 330, a dielectric loss of 8.4% and a piezoelectric coefficient of 5.5 C m −2 . This work demonstrates the feasibility of transparent piezoelectric films, which has a potential to opening the way to flexible and invisible devices.

A stable and effective HTL leads to a record efficiency of 18.2% for ultra-thin (750 nm) CIGS solar cells.

In this study, we investigate the non-linear pyroelectric energy conversion potential of titanium doped lead scandium tantalate Pb(Sc0.5Ta0.5)(1-x)TixO3 (x = 0, 0.05 and 0.1) thin films on c-sapphire substrates using the solgel technique. Doping with Ti4+ ions increased the transition temperature from 30 degrees C (x = 0) to 85 degrees C (x = 0.1). Indirect measurements using the Olsen cycle indicate that Pb(Sc0.5Ta0.5)(1-x)TixO3 thin films, with x = 0.05 and 0.1, yield energy densities of 2.5 and 3.06 J cm(-3), respectively. Additionally, they reach up to 30 % and 18 % of Carnot efficiency, respectively, for a 10 K temperature span close to their transition temperatures. Furthermore, these doped films could be incorporated in a multi-stage device to expand the harvesting temperature range and enhance the performance of the device. A 27 % increase in energy output is calculated for a three-stage device using Pb(Sc0.5Ta0.5)(1-x)TixO3 (x = 0, 0.05, and 0.1) compared to a similar device consisting of undoped thin films (x = 0) under identical electrical and thermal cycling conditions. These results highlight the potential of Pb (Sc0.5Ta0.5)(1-x)TixO3 thin films and show promise for developing Pb(Sc0.5Ta0.5)(1-x)TixO3 multilayer capacitors to realize macroscopic multi-material cascade devices with varying transition temperatures for efficient thermal energy harvesting in the future.

Reducing the thickness of Cu(In,Ga)Se2 solar cells is a key objective in order to reduce production cost and to improve sustainability. The major challenge for sub-micron Cu(In,Ga)Se2 cells is the recombination at the backside. In standard Cu(In,Ga)Se2 backside recombination is suppressed by a bandgap gradient, acting as a back surface field. This gradient is difficult to maintain in sub-micron thick absorbers. In this study, a hole transport layer passivates the back contact and enables efficient sub-micron Cu(In,Ga)Se2 solar cells without the need of a Ga gradient. The backside passivation by the hole transport layer is as effective as an optimized Ga gradient, resulting in a significant increase in open-circuit voltage by 80 mV in comparison to the reference sample without passivation. Moreover, the hole transport layer exhibits good transport properties, leading to a fill factor as high as 77

Acoustic haptic technology adds touch sensations to human-machine interfaces by integrating piezoelectric actuators onto touchscreens. Traditional piezoelectric haptic technologies use opaque lead-containing ceramics that are both toxic and visible. We have developed a highly transparent lead-free piezoelectric haptic device using potassium sodium niobate (KNN) and transparent conductive oxide thin films. The KNN film, grown on glass, exhibits a pure perovskite phase and a dense microstructure. This device achieves up to 80 Acoustic haptic technology enhances touch interfaces but often relies on opaque, toxic lead-based ceramics. Here, the authors develop a transparent, lead-free piezoelectric device using potassium sodium niobate and conductive oxide films, achieving superior transmittance and effective acoustic resonance, offering a promising alternative for safer, more versatile haptic applications.

In a recent paper from Joule, Bo and co-workers reveal a new application related to electrocaloric materials. Whereas these materials are generally considered for cooling applications, here they show that electrocaloric polymers can be useful for thermal camouflage by providing very fast temperature change, a property that the well-known Joule effect cannot provide.

High‐efficiency Cu(In,Ga)Se 2 solar cells rely on Ga grading to mitigate back surface recombination. However, the inhomogeneous absorber has drawbacks, including increased non‐radiative loss and inadequate absorption. Therefore, literatures demand a paradigm shift of using a hole‐transport layer to passivate the back surface. Herein, a functional hole‐transport layer is demonstrated as an alternative to Ga grading. The novel hole‐transport layer is prepared as a double‐layer: co‐evaporated CuGaSe 2 covered by solution combustion synthesis prepared In 2 O 3 . As demonstrated by micrographs, elemental mapping, and photoluminescence spectroscopy, the oxide layer improves thermal stability and prevents Ga diffusion. However, during the absorber deposition, a complete ion exchange of In and Ga converts CuGaSe 2 /In 2 O 3 into CuInSe 2 /GaO x . Incorporating this hole‐transport layer in co‐evaporated nongraded CuInSe 2 solar cells leads to significantly increased minority carrier lifetime from 5 to 113 ns, yielding an 80 meV improvement in quasi‐Fermi‐level splitting. The devices exhibit improved open‐circuit voltage, as well as a promising fill factor of over 71%, indicating good hole‐transport properties. In these results, the passivation effect and good hole‐transport properties of the hole‐transport layer are experimentally demonstrated. Thus, high‐efficiency solar cells can be achieved by using a functional hole‐transport layer without relying on Ga grading.

Since the discovery of ferroelectricity in HfO_2 thin films, significant research has focused on Zr-doped HfO_2 and solid solution (Hf,Zr)O_2 thin films. Functional properties can be further tuned via multilayering, however, this approach has not yet been fully explored in HfO_2-ZrO_2 films. This work demonstrates ferroelectricity in a 50 nm thick, solution-processed HfO_2-ZrO_2 multilayer film, marking it as the thickest such film to date exhibiting ferroelectric properties. The multilayer structure was confirmed through transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy, with high-resolution TEM revealing grain continuity across multiple layers. This finding indicates that a polar phase in the originally paraelectric ZrO_2 layer, can be stabilized by the HfO_2 layer. The film attains a remanent polarization of 8 uC/cm^2 and exhibits accelerated wake-up behavior, attributed to its higher breakdown strength resulting from the incorporation of multiple interfaces. These results offer a faster wake-up mechanism for thick ferroelectric hafnia films.

Non-linear pyroelectric energy harvesting using ferroelectric thin films exhibits high energy conversion, primarily due to their large breakdown field compared to bulks. Here, we report the pyroelectric energy conversion potential of lead scandium tantalate, Pb(Sc 1/2 Ta 1/2 )O 3 (PST) thin film fabricated on a c-sapphire substrate using chemical solution deposition. To enable the application of high electric field and to assess the pyroelectric energy conversion performance, interdigitated electrodes were deposited on the PST thin film. A maximum harvested energy density of 9.1 J cm -3 per cycle was deduced from polarization measurements in films undergoing an Olsen cycle between 0 degrees C and 150 degrees C when the electric field was varied between 50 and 1500 kV/cm. Furthermore, PST thin films can reach up to 27 % of Carnot efficiency for a temperature interval of 10 K between 30 degrees C and 40 degrees C. This study highlights the significance of PST thin films for electro-thermal energy harvesting and promising opportunities for enhancing the conversion efficiency and power density using thin films or thin film multi-layer capacitors in the future for thermal energy harvesting.

Integration of thin-film oxide piezoelectrics on glass is imperative for the next generation of transparent electronics to attain sensing and actuating functions. However, their crystallization temperature (above 650 °C) is incompatible with most glasses. We developed a flash lamp process for the growth of piezoelectric lead zirconate titanate films. The process enables crystallization on various types of glasses in a few seconds only. The functional properties of these films are comparable to the films processed with standard rapid thermal annealing at 700 °C. A surface haptic device was fabricated with a 1 μm-thick film (piezoelectric e 33 ,f of −5 C m −2 ). Its ultrasonic surface deflection reached 1.5 μm at 60 V, sufficient for its use in surface rendering applications. This flash lamp annealing process is compatible with large glass sheets and roll-to-roll processing and has the potential to significantly expand the applications of piezoelectric devices on glass.