An insight into the analogies, state-of-the-art technologies, concepts, and prospects under the umbrella of perovskite materials (both inorganic-organic hybrid halide perovskites and ferroelectric perovskites) for future multifunctional energy conversion and storage devices is provided. Often, these are considered entirely different branches of research; however, considering them simultaneously and holistically can provide several new opportunities. Recent advancements have highlighted the potential of hybrid perovskites for high-efficiency solar cells. The intrinsic polar properties of these materials, including the potential for ferroelectricity, provide additional possibilities for simultaneously exploiting several energy conversion mechanisms such as the piezoelectric, pyroelectric, and thermoelectric effect and electrical energy storage. The presence of these phenomena can support the performance of perovskite solar cells. The energy conversion using these effects (piezo-, pyro-, and thermoelectric effect) can also be enhanced by a change in the light intensity. Thus, there lies a range of possibilities for tuning the structural, electronic, optical, and magnetic properties of perovskites to simultaneously harvest energy using more than one mechanism to realize an improved efficiency. This requires a basic understanding of concepts, mechanisms, corresponding material properties, and the underlying physics involved with these effects.

Mutual Insight on Ferroelectrics and Hybrid Halide Perovskites: A Platform for Future Multifunctional Energy Conversion.

This review provides a detailed overview of the energy harvesting technologies associated with piezoelectric materials along with the closely related sub-classes of pyroelectrics and ferroelectrics. These properties are, in many cases, present in the same material, providing the intriguing prospect of a material that can harvest energy from multiple sources including vibration, thermal fluctuations and light. Piezoelectric materials are initially discussed in the context of harvesting mechanical energy from vibrations using inertial energy harvesting, which relies on the resistance of a mass to acceleration, and kinematic energy harvesting which directly couples the energy harvester to the relative movement of different parts of a source. Issues related to mode of operation, loss mechanisms and using non-linearity to enhance the operating frequency range are described along with the potential materials that could be employed for harvesting vibrations at elevated temperatures. In addition to inorganic piezoelectric materials, compliant piezoelectric materials are also discussed. Piezoelectric energy harvesting devices are complex multi-physics systems requiring advanced methodologies to maximise their performance. The research effort to develop optimisation methods for complex piezoelectric energy harvesters is then reviewed. The use of ferroelectric or multi-ferroic materials to convert light into chemical or electrical energy is then described in applications where the internal electric field can prevent electron–hole recombination or enhance chemical reactions at the ferroelectric surface. Finally, pyroelectric harvesting generates power from temperature fluctuations and this review covers the modes of pyroelectric harvesting such as simple resistive loading and Olsen cycles. Nano-scale pyroelectric systems and novel micro-electro-mechanical-systems designed to increase the operating frequency are discussed.

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Piezoelectric and ferroelectric materials and structures for energy harvesting applications

This review covers energy harvesting technologies associated with pyroelectric materials and systems. Such materials have the potential to generate electrical power from thermal fluctuations and is a less well explored form of thermal energy harvesting than thermoelectric systems. The pyroelectric effect and potential thermal and electric field cycles for energy harvesting are explored. Materials of interest are discussed and pyroelectric architectures and systems that can be employed to improve device performance, such as frequency and power level, are described. In addition to the solid materials employed, the appropriate pyroelectric harvesting circuits to condition and store the electrical power are discussed.

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Pyroelectric materials and devices for energy harvesting applications

Pyroelectric cells based on fabricated screen-printed PZT and commercial PVDF films are proposed as thermal energy harvesting sources in order to supply low-power autonomous sensors. The cells are electrically modelled as a current source in parallel with output impedance. Heating and cooling temperature fluctuations generated by air currents were applied to the pyroelectric converters. The generated currents and charges were respectively in the order of 10 −7  A and 10 −5  C for temperature fluctuations from 300 K to 360 K in a time period of the order of 100 s, which agrees with the theoretical model. Parallel association of cells increased the generated current. The dependence of the generated current on relevant technological parameters has been also characterized. Finally, current from cyclic temperature fluctuations was rectified and stored in a 1 μF load capacitor. Energies up to 0.5 mJ have been achieved, enough to power typical autonomous sensor nodes during a measurement and transmission cycle.

Thermal energy harvesting through pyroelectricity

This paper deals with small-power energy harvesting from heat. It can be achieved using both thermoelectric and pyroelectric effects. In the first case, temperature gradients are necessary. The main difficulty of thermoelectric energy harvesting is imposing a large temperature gradient. This requires huge heat flows because of the limited surface heat exchanges and the large heat conductivity of thermoelectric materials. This results in a drastic decrease of power and the efficiency of conversion. In case of pyroelectric energy harvesting, a time varying temperature is necessary. Although such a temperature time profile is hard to find, the overall optimization is easier than the thermoelectric strategy. Indeed, it depends much less on heat exchange between the sample and the outer medium, than on heat capacity that dimensions optimization may easily compensate. As a consequence, it is shown that the efficiency and output power may be much larger using pyroelectric energy harvesting than thermoelectric methods. For instance, using a limited temperature gradient due to the limited heat exchange, a maximum efficiency of 1.7% of Carnot efficiency can be expected using a thermoelectric module. On the contrary, a pyroelectric device may reach an efficiency up to 50% of Carnot efficiency. Finally, an illustration shows an estimation of the output power that could be expected from natural time variations of temperature of a wearable device. Power peaks up to 0. 2m W cm −3 were found and a mean power of 1 μ Wc m −3 on average was determined within 24 h testing.

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On thermoelectric and pyroelectric energy harvesting

The effect of the type of power cycle upon the amount of output electrical work for a pyroelectric converter has been measured. Output electrical energy densities are reported for ceramic lead zirconate modified with Sn4+ and Ti4+ in the execution of a variety of thermal‐electrical cycles. The effect upon the energy density due to changes in the voltage cycle limits and changes in the load resistance were also studied. A conversion cycle which is an electric analog of the Ericsson cycle is shown to yield the largest output energy density (100 mJ/cm3 for a 12.6 K temperature excursion and a 28‐kV/cm electric field excursion).

Pyroelectric conversion cycles

Copolymers of vinylidene fluoride–trifluoroethylene P(VDF‐TrFE) exhibit large piezoelectric and pyroelectric effects. In addition to the most common application of the pyroelectric effect (radiant detection) it is possible to convert heat directly into electrical energy by pyroelectric conversion. This study reports the first pyroelectric conversion cycle to be measured for the copolymer P(VDF‐TrFE). It is found that standard isothermal D‐E hysteresis loop measurements are not necessarily accurate predictors of pyroelectric conversion performance for this material. Conduction effects are found to obscure the observation of conversion cycles in most cases for the presently available materials. In spite of these difficulties, a conversion cycle was measured whose output electric energy density was 30 mJ/cm3. The output density is 15 times larger than any other polymer previously measured .

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Pyroelectric conversion cycle of vinylidene fluoride‐trifluoroethylene copolymer

A single-stage regenerative pyroelectric heat engine has been built and tested The pyroelectric engine converts heat directly into electrical energy The efficiency of the conversion process was directly measured (the first such measurement for any pyroelectric conversion process) The measured 04% efficiency is 16 times larger than the so-called van der Ziel limit Further improvements of efficiency are discussed The engine's power density (at 013Hz) was 17 Watt per liter of ferroelectric material This early progress indicates that multi-stage pyroelectric engines operating at higher frequencies may achieve 2 kW per liter with efficiencies of 10% to 20%

A pyroelectric energy converter which employs regeneration

A regenerative pyroelectric converter employing multiple staging has been constructed and tested. Operating between the temperatures of 150°C and 180°C the device converted heat into electrical energy. Measurements of the conversion efficiency and power density as functions of frequency (0.05 to 0.3 Hz) are reported. The converter's maximum power density was 33 Watts per liter of pyroelectric ceramic at 0.26 Hz.

Cascaded pyroelectric energy converter

Copolymers of vinylidene fluoride‐trifluoroethylene P(VDF‐TrFE) exhibit large piezoelectric and pyroelectric effects. In addition to the most common application of the pyroelectric effect (radiant detection) it is possible to convert heat directly into electrical energy by pyroelectric conversion. This study reports the first measurements of high (constant) field pyroelectric effects of P(VDF‐TrFE) which are relevant to pyroelectric conversion. Electric displacement changes which result from temperature changes of the copolymer were measured for thermal cycling from room temperature to 90 °C at fields up to 1 MV/cm. The displacement changes (0.1–0.3 μ C/cm2) were dependent upon the molar ratio of the constituent monomers. The resistivity of the copolymer was also measured in the temperature range 20 to 90 °C and was found to vary from 1012 to 1016Ω cm depending on monomer ratio, temperature, field, and time. The resistivity and displacement change data are discussed in terms of predicted pyroelectric ener...

Randall B. Olsen

Papers

Pyroelectric conversion cycles

Pyroelectric conversion cycle of vinylidene fluoride‐trifluoroethylene copolymer

A pyroelectric energy converter which employs regeneration

Cascaded pyroelectric energy converter

High electric field resistivity and pyroelectric properties of vinylidene fluoride‐trifluoroethylene copolymer