Solar Thermoelectric Generator Research Articles

A Superhydrophobic Self-Cleaning Flexible Hydrogel for Solar Thermoelectric Power Generation

A Superhydrophobic Self-Cleaning Flexible Hydrogel for Solar Thermoelectric Power Generation

Mussel-Inspired Self-Adhesive and Tough Hydrogels for Effectively Cooling Solar Cells and Thermoelectric Generators.

Adhesive hydrogel-based evaporative cooling, which necessitates no electricity input, holds promise for reducing energy consumption in thermal management. Herein, inspired by the surface attachment of mussel adhesive proteins via abundant dynamic covalent bonds and noncovalent interactions, we propose a facile strategy to fabricate a self-adhesive cooling hydrogel (Li-AA-TA-PAM) using a copolymer of acrylamide (AM) and acrylic acid (AA) as the primary framework. The monomers formed hydrogen bonds between their carboxyl and amide groups, while tannic acid (TA), rich in catechol groups, enhances the adhesion of the hydrogel through hydrogen bonding. The hydrogel demonstrated strong adhesion to various material surfaces, including plastic, ceramic, glass, and metal. Even under high-speed rotation, it still maintains robust adhesion. The adhesion strength of the Li-AA-TA-PAM hydrogel to aluminum foil reached an impressive value of 296.875 kPa. Interestingly, the excellent contact caused by robust adhesion accelerates heat transfer, resulting in a rapid cooling performance, which mimics the perspiration of mammals. Lithium bromide (LiBr) with hydroactively sorptive sites is introduced to enhance sorption kinetics, thereby extending the effective cooling period. Consequently, the operation temperature of commercial polycrystalline silicon solar cells was reduced by 16 °C under an illumination of 1 kW m-2, and the corresponding efficiency of energy conversion was increased by 1.14%, thereby enhancing the output properties and life span of solar cells. The strategy demonstrates the potential for refrigeration applications using viscous gels.

Impedance spectroscopy analysis of thermoelectric modules under actual energy harvesting operating conditions and a small temperature difference

Thermoelectric (TE) devices can convert heat into electricity and have gained great interest as energy harvesters in many applications, such as self-powered sensors, solar TE generators and industrial waste heat recovery. Not many techniques are usually available for their characterization under operating conditions. Consequently, only current-voltage (power output) curves are typically reported to account for their performance, which provide limited information. Impedance spectroscopy, which has been mainly applied to the study of TE modules suspended in air or vacuum, has the advantage to be used under operating conditions. Here, we exploit this advantage and provide an in-depth analysis of the impedance response of standard TE devices when they operate under a small temperature difference. First, we derive the physical models (equivalent circuits) for the two most common operating conditions: (i) constant temperature difference and (ii) constant heat power input. Then, we use the obtained equivalent circuit to successfully fit experimental impedance measurements in both operating modes, which show significant differences. From the fittings, it is possible to obtain the thermal contact resistance between the TE device and the heat exchangers (heat source and heat sink) among other key parameters. In addition, we analyze the variations found in the impedance spectra for different current output levels. Moreover, we show how different electrical resistances, extracted from the impedance results, directly relate to the slope of the I-V curve (power output), and can provide very valuable information about the different processes that determine its value. All these results establish impedance spectroscopy as a very powerful tool to characterize TE devices under operating conditions and as a method that can provide highly valuable insights into their performance.

Lead free A2NaInI6 (A = Cs, Rb, K) double perovskites for optoelectronic and thermoelectric applications

Alkali metal substitution in double perovskites is an appropriate approach to deliberate tuning of band edges which play a vital role in bandgap engineering of emerging semiconducting materials. Here we tuned the optoelectronic behavior by carefully engineering the band edges in A2NaInI6 (A = Cs, Rb, K) systems and by tuning the alkali atoms at A site using density functional theory based WIEN2K code. First of all, the unit cell is relaxed to find the optimized lattice parameters. The substitution of smaller-sized cation at the A site leads to the reduction in lattice parameter which shifts the absorption edge towards a shorter wavelength and reduces the bandgap energy. The value of bandgap energy is noticed at 1.60 eV for Cs2NaInI6 which increases to 1.65 and 1.70 eV for Rb2NaInI6 and K2NaInI6 respectively. The computation of the elastic constant’s dependent modulus of elasticity and the Pugh and Poisson ratio confirm their brittle nature. Their viability for solar-thermoelectric generators is carried out by computing the temperature-dependent transport parameters using the BoltzTrap code showing the potential of these systems for solar thermoelectric generators.

A Novel Application of a Parabolic Trough Collector for Solar Cooking, Thermal Storage and Thermoelectric Energy Harvesting

The work here involves designing a solar solution for safe cooking and low-power generation intended for application in rural communities. A system was developed that combines Concentrated Solar Power (CSP) and Thermoelectric Generator (TEG) technologies. The CSP provides heat for clean cooking, and the excess heat is harvested by the TEG and converted into electrical power. A storage tank was integrated into the system, storing excess energy and serving as the medium for indirect cooking and supplying the heat required by the TEG. The Parabolic Trough Collector, having a resulting average thermal efficiency value of 21%, provided the useful energy to store over 4.25kWh of heat in the tank during the initial testing of the system. The TEG developed has four Peltier modules and attained 23W - over 80% of their rated power and a maximum conversion efficiency of 4.14% at a temperature difference of 220°C between the cold and hot surfaces of the generator. During the experiment, the TEG operation was limited to only four hours before subjecting a no-load test to assess the total energy storable from the system. The initial results from the test carried out here show the potential of the hybrid system in storing energy in the tank for an extended period and simultaneous operation of the TEG. Excess energy stored can be utilised further in providing the heat required for cooking or further electrical power generation.

Unveiling the DFT perspectives on structural, elastic, optoelectronic, and thermoelectric properties of zirconate perovskites XZrO3 (X = Ca, Sr, Ba)

A thorough comparative study of lead free zirconate perovskite XZrO3 (X = Ca, Sr, Ba) is carried out employing WIEN2k which is a density functional theory based code. A good agreement between reported synthesis and the theoretical results is observed. BaZrO3 can be inferred as the most stable compound among XZrO3 (X = Ca, Sr, Ba) as its ground state energy is lowest. According to the Burn-Haun criterion, the compounds under research are mechanically stable. The ductile nature, anisotropy, and reasonable resistance to deformation in response to external stress are observed. The semiconducting nature of the compounds is observed having indirect band gaps with values of 3.25 eV, 3.71 eV, and 3.80 eV. Exceptional optical absorption peaks for the investigated compounds can be observed in UV region (around 5.0 eV) which suggests their numerous optoelectronic applications within UV. XZrO3 (X = Ca, Sr, Ba) are active optical materials as their refractive inrdex n(ω) occurs in the range of 1.0 and 2.0. Thermoelectric properties of these compounds are also very promising since the large Seebeck coefficients (∼2250–2700 μV/K), large power factor values (∼1011 W/mK2s), and figure of merits are very close to the unity are observed. The mechanical stability and ductility, and the appealing optical and thermoelectric properties of the examined compounds persuade us that these compounds may play a significant role for numerous industrial applications like solar cells, LEDs, sensors, thermoelectric generators and other energy conversion devices in the future.

High-Entropy Photothermal Materials.

High-entropy (HE) materials, celebrated for their extraordinary chemical and physical properties, have garnered increasing attention for their broad applications across diverse disciplines. The expansive compositional range of these materials allows for nuanced tuning of their properties and innovative structural designs. Recent advances have been centered on their versatile photothermal conversion capabilities, effective across the full solar spectrum (300-2500nm). The HE effect, coupled with hysteresis diffusion, imparts these materials with desirable thermal and chemical stability. These attributes position HE materials as a revolutionary alternative to traditional photothermal materials, signifying a transformative shift in photothermal technology. This review delivers a comprehensive summary of the current state of knowledge regarding HE photothermal materials, emphasizing the intricate relationship between their compositions, structures, light-absorbing mechanisms, and optical properties. Furthermore, the review outlines the notable advances in HE photothermal materials, emphasizing their contributions to areas, such as solar water evaporation, personal thermal management, solar thermoelectric generation, catalysis, and biomedical applications. The review culminates in presenting a roadmap that outlines prospective directions for future research in this burgeoning field, and also outlines fruitful ways to develop advanced HE photothermal materials and to expand their promising applications.

Recent advances of spectrally selective absorbers: Materials, nanostructures, and photothermal power generation

With the increasing development of photothermal techniques in various fields, particularly concentrated solar power (CSP) systems and solar thermoelectric generators (STEGs), the demand for high-performance spectrally selective absorbers (SSAs) has grown significantly. These SSAs are essential in achieving high solar absorption and minimal infrared thermal loss, thereby significantly enhancing solar utilization efficiency. This need becomes particularly critical in CSP systems, where high temperatures are pivotal for improved efficiency. However, the necessity for high temperatures imposes stringent requirements on the fabrication of SSAs, given the inherent trade-off between optical performance and thermal stability. SSAs typically require nanoscale thin films, but they are prone to oxidation and diffusion at high temperatures. Recent developments in photothermal materials, including ceramic composites, MXenes, high-entropy materials, and graphene, offer promising solutions to enhance SSAs’ performance. This review article provides a comprehensive evaluation of the latest advancements in these emerging photothermal materials. We summarize the strategies for integrating these advanced materials with already established nanostructures, which is a highly promising approach for the development of advanced SSAs. Additionally, the review explores the application of SSAs in CSP systems and STEGs to boost power generation efficiency. We conclude by summarizing the challenges and opportunities in the field of high-temperature SSAs, offering valuable insights into the development of high-performance SSAs and their role in solar-thermal power generation systems.

Polyol-assisted efficient hole transfer and utilization at the Si-based photoanode/electrolyte interface

The sluggish kinetics of the anodic oxygen evolution reaction significantly restricts the efficiency of silicon (Si)-based photoelectrochemical (PEC) cells. In this study, we employ microfabrication technology to batch-prepare reproducible Si substrates, and develop a facile electrodeposition technique to load high-quality nickel film onto the substrates. Innovatively, we introduce energetically favorable polyols (such as glycerol, propylene glycol, and ethylene glycol) into the electrolyte, resulting in a remarkably low onset potential and a high hole injection efficiency during the PEC oxidation process. Taking glycerol as an example, in-situ impendence spectra provide real-time evidence for the accelerated hole transfer and utilization at the photoanode/electrolyte interface in the presence of glycerol. Mechanistic studies further reveal that glycerol undergoes synergistic oxidation mediated by holes and catalysts. Finally, by intergrating a solar thermoelectric generator into a PEC polyol oxidation cell, the self-powered system demonstrates promising potential for producing valuable products solely by harnessing solar energy.

Mathematical analysis of the solar assisted thermoelectric generator

The direct conversion of solar energy into electrical energy is primarily dependent on the photovoltaic systems. However, in the last few decades, researchers have shown interest to work on the thermoelectric modules for direct conversion of solar thermal energy into electrical energy based on the Seebeck effect. This research paper provides a comprehensive analysis of various Solar Thermoelectric Generator (STEG) designs, focusing on their conversion efficiencies. Despite the comparatively lower efficiency of STEG in comparison to photovoltaic (PV) cells, owing to limitations in the figure of merit value and temperature differences between hot and cold sides of the thermoelectric modules, this study proposes strategies for enhancement. Approaches include the development of materials with higher figure of merit values, design optimization, solar tracking, heat storage systems, and efficient heat sink designs. Also, Mathematical analysis of the power and efficiency calculation of a STEG has been presented on the basis of some fundamental and derived mathematical equations. The overall efficiency of STEG, a product of Opto-thermal Efficiency and thermoelectric module efficiency, is explored, identifying an optimal hot side temperature for maximum efficiency. Module mismatch analyses for series and parallel connections are also derived, underscoring conditions for mitigating power loss. These findings serve as guidelines for designing more feasible and efficient STEG systems, with considerations for economic viability, sustainability and greenhouse gas reduction throughout the life cycle.

Fabrication of low-cost flexible thermoelectric generator using conductive HB graphite paint operated by solar radiation

Paper-based flexible thin film thermoelectric generators have emerged as a promising and feasible alternative to organic and inorganic conductors due to their ability to operate at room temperature within a limited temperature range. Here, a flexible solar thermoelectric generator (STEG) designed from a single material has been introduced, prepared by a simple painting method. We prepared HB graphite-based conductive paint and demonstrated a very unique method to design flexible STEG devices. The graphite paint shows p-type semiconductive behaviour, while, in conjunction with the polyethyleneimine (PEI) polymer, it acts as an n-type material. Based on the transport properties, the paint appears to be a good candidate for designing STEG devices. At room temperature, the power factor of 378 nW m−1 K−2 for p-type paint and 1.51 nW m−1 K−2 for n-type paint is obtained. In order to examine flexibility over the long term, the performance of the material was inspected through 300 repeated cycles, and transport properties (conductivity) were found to increase from 21 700 S m−1 to 73 500 S m−1 due to the excellent emulsifying properties of gum Arabic, which were confirmed by field emission scanning electron microscope analysis. To evaluate the performance of the thermoelectric (TE) generator, eight pairs of p–n legs are fabricated on normal copier (80 GSM) paper, and an output voltage of ∼0.1 mV K−1 (∼5.5 mV) for a temperature gradient T of up to ∼60 K was achieved. Further, the performance of flexible TE devices can be improved by increasing the number of thermoelectric legs and by sandwiching the device between Kapton tapes. Our work suggests a promising and simple approach to achieving cost-effective conversion of solar energy into electricity and highlights the potential of flexible STEGs for low-power applications.

Unidirectionally Structured Magnetic Phase-Change Composite Based on Carbonized Polyimide/Kevlar Nanofiber Complex Aerogel for Boosting Solar-Thermo-Electric Energy Conversion.

To realize highly efficient solar-thermo-electric energy conversion for clean electricity power generation, we have developed a new type of unidirectionally structured magnetic phase-change composite comprising a carbonized polyimide (C-PI)/Kevlar nanofiber (KNF) complex aerogel as a 3D carbon skeleton porous supporting material, CoFe2O4 nanoparticles as a magnetic additive, polyethylene glycol (PEG) as a phase-change material, and polypyrrole as a photothermal absorption coating layer. The as-fabricated C-PI/KNF complex aerogel exhibits a unidirectional microstructure, high porosity, robust skeleton frame, ultralight weight, and high thermal conductance. Featured with such unique structure and characteristics, the complex aerogel can offer an effective heat and electron transfer method to ensure highly efficient solar-thermal conversion and photothermal energy storage of the developed composite. The developed composite exhibits a high latent heat capacity of over 150 J g-1, outstanding shape stability along with a low leakage of 0.2 wt %, good thermal cycling stability, and high photothermal conversion efficiency of 84.8%. Based on the Seebeck effect, a solar thermoelectric generation system (STEGS) was constructed with the hot side coupled with the developed composite and the cold side immersed in air and ice water. Under 2.0 kW m-2 solar irradiation, the developed STEGS in ice water obtained maximum output voltage and current of 259.7 mV and 27.1 mA, respectively, which are significantly higher than those in air. The output power of the developed STEGS in an ice water environment is 50.6% higher than that in air under 4.0 kW m-2 solar irradiation. More importantly, the developed STEGS in ice water continuously generated output voltage and current for about 810 s without solar irradiation thanks to the latent heat release by the PEG component within the developed composite. In addition, the introduction of magnetic CoFe2O4 can accelerate solar-thermal conversion through periodic electron motion by the Néel relaxation or Brownian relaxation. This resulted in an increase in the maximum output voltage and current by 13.7 and 11.5%, respectively, under an alternating magnetic field as a result of the magnetism-accelerated solar-thermo-electric conversion. This study offers an innovative approach for developing PCM-based advanced functional materials for solar energy utilization in clean and sustainable electricity generation.

Sustainable thermal energy harvest for generating electricity

Electricity is the lifeblood of modern society. However, the predominant source of electricity generation still relies on non-renewable fossil fuels, whose combustion releases greenhouse gases contributing to global warming. The increasing demand for energy and escalating environmental concerns necessitate proactive measures to develop innovative green energy technologies capable of both cooling the Earth and generating electricity. Here, we look forward to an interdisciplinary power system integrating solar absorbers, radiative coolers, and thermoelectric generators. This system can simultaneously harvest thermal energy from the sun and from cold space, thereby transforming the challenges posed by global warming into opportunities for the production of clean electricity. We underscore recent advancements in this field and address key challenges while also exploring forward-looking opportunities in the foreseeable future. The proposed integrated energy technology achieves uninterrupted power supply through the unrestricted capture of thermal energy, offering a robust alternative pathway for next-generation sustainable energy technologies.

Tuning the optoelectronic and thermoelectric properties of vacancy-ordered halide perovskites Cs2Ge(1-x)PtxCl6 (x=0, 0.25, 0.50, 0.75 and 1.00) via substitutional doping of Pt using first-principles approach

Vacancy-ordered halide perovskites have gained considerable attention from researchers regarding non-traditional energy harvesting applications like solar cells and thermoelectric generators. However, in most of the reported cases, band gaps are larger (>3.5eV) consequently the efficiency of solar cells and thermoelectric generators becomes low. Currently, we studied non-toxic and stable vacancy-ordered halide perovskites Cs2GeCl6 and tuned its band gap via substitutional doping of Pt (0, 25, 50, 75, and 100 %) using the first-principles approach. The band gap engineering strategy of Pt doping effectively decreased the band gaps (up to 2.50eV) hence, the more attractive optical and thermoelectric parameters are obtained for instance; high absorption coefficients (∼105 cm−1), low reflectivity (∼0.3–10 %), high optical conductivity (∼1015 sec−1), and large figure of merits (∼1). Based on these enhanced optical and thermoelectric performance parameters, the Pt doping strategy can be taken as an effective practice to tune the band gap significantly in order to stimulate the performance of future solar cells and thermoelectric generators.

Effect of nonuniform solar radiation on the performance of solar thermoelectric generators

Solar radiation must be concentrated before irradiating hot sides in solar thermoelectric generators (STEGs) to increase the temperature difference between hot and cold sides and thus enhance output performance. However, concentrated solar radiation is often nonuniform. This condition affects the output performance of STEGs. Herein, a thermal–electric coupled model of STEGs was constructed to investigate the thermoelectric performance of STEGs under nonuniform solar radiation. Results demonstrate that when the concentration ratio is low, increasing nonuniformity facilitates the increase in the output power of STEGs. When the concentration ratio is 60, output power increases by a maximum of 3.05 %, whereas the average temperature difference decreases by 4.44 K. When the concentration ratio is high, STEG output power peaks under a specific nonuniformity, and some thermoelectric legs at the edges of STEGs turn into load, affecting the overall STEG output performance. When the cold-side cooling performance is poor, the solar radiation input to STEGs should be made as uniform as possible to ensure the output performance and safe operation of STEGs. The results of this study provide guidance for the design of efficient STEGs.

EVALUATION OF HEAT LOSSES IN A NONCONCENTRATED SOLAR THERMOELECTRIC GENERATOR WITH SPECTRALLY SELECTIVE ABSORBERS

Solar thermoelectric generator (STEG) has been widely studied in optical and thermal concentrating fields, and the spectral properties are mainly focused on the solar spectrum. However, limited attention has been paid to STEG without any concentrators and in the full spectral range. Therefore, in this work, a thermal-electrical coupled mathematical model for STEG systems is developed according to thermal resistance networks to investigate heat losses above the absorber and power generation performance. For the ideal selective absorber and emitter (ISAE) system, the main heat losses from the absorber occur due to radiative cooling to the sky as well as for the ideal broadband absorber (IBA) system, as opposed to convection and ambient radiative losses. These sky radiative cooling losses account for approximately 83.8% and 73.7% of the total heat losses, respectively. The total water vapor has the greatest impact on radiative cooling power compared to other heat losses, and the radiative cooling power for the IBA and ISAE modules decreases significantly, with a decline of nearly 62.93 W/m<sup>2</sup> and 62.97 W/m<sup>2</sup> from 129.6 W/m<sup>2</sup> and 129.7 W/m<sup>2</sup>, respectively. Wind speed has the largest effect on convective heat loss, and for every 1 m/s increase in speed, the increment of convective loss is approximately constant with the average increment of 8.76 W/m<sup>2</sup>. Elevated ambient temperatures result in decreased heat loss across all forms. In light of its environmentally friendly characteristics, this paper offers recommendations on enhancing the system design of STEG aiming to minimize heat loss and enhance system performance.

A day-night solar thermoelectric generator enabled by phase change material and forced water cooling

Solar thermoelectric generators (STEGs), which are capable of directly converting solar energy to electricity, are essential to many potential applications in addition to photovoltaics. It is of great importance to advance the design of STEGs to significantly boost the output performance by combining solar selective absorbers, cooling technologies and phase change materials. In this work, a novel day-night STEG integrated with transparent phase change materials of methyl palmitate and forced water cooling (PCM-STEG-WC) is proposed. The fabricated solar selective absorber exhibits a high solar absorption of 96.05 %, leading to its surface temperature up to 100 °C under 1-sun illumination (1 kW m−2), while the surface temperature of conventional thermoelectric module is only about 44.4 °C. Consequently, the temperature difference between hot and cold ends can be significantly increased to 5.6 °C from 2 °C, about 2.8 times higher than the conventional thermoelectric module. Moreover, this unconcentrated PCM-STEG-WC can realize a power level of 6.42 mW associated with output voltage of 307.3 mV at a solar density of 1 kW m−2, which is about 9 times higher than that of conventional thermoelectric module (35.5 mV). Additionally, the hot end temperature of PCM-STEG-WC only decays by 17 % in 100 s without solar radiation. To demonstrate the effectiveness of the PCM-STEG-WC in power generation at night, a single red LED is completely powered. Finally, this study may provide a promising strategy to develop high-performance STEGs for remote applications.

Insight into the structural, elastic, phonon dispersions, and optoelectronic properties of Cs2YXCl6 (X = In, Tl) double perovskites for solar cells and energy conversion applications

Due to their lack of lead, stability, and outstanding performance, double perovskites have emerged as a prominent subject of study in solar cell research. Thus, we present an analysis of the structural, elastic, electronic, and optical characteristics of Cs2YXCl6 (X = In, Tl) with regard to their applications in solar cells and thermoelectric generators. The structural stability has been validated by observing the thermodynamic stability, as evidenced by the negative formation energy and the fitting of the Birch-Murnaghan equation of state. The confirmation of structural stability in our materials is further supported by the absence of imaginary frequencies in the phonon dispersion calculations. The mechanical stability of both compounds is established by the relationship between their elastic constants, specifically C11 - C12 > 0, C11 > 0, C11 + 2 C12 > 0, and B > 0. However, it should be noted that these materials are characterized as mechanically anisotropic and ductile. By employing the highly promising Tb-MBj potential, the band gaps of Cs2YInCl6 and Cs2YTlCl6 have been calculated to be 4 eV and 0.9 eV, respectively. Cs2YInCl6 is categorized as an insulator, whereas Cs2YTlCl6 is considered a semiconductor. This distinction arises from the higher atomic mass of Tl in comparison to In, which results in elevated energy levels within the conduction band. A comprehensive investigation of the optical properties of both compounds was conducted within the energy range of 0 eV to 40 eV. It was found that these compounds exhibit significant absorption and optical conductivity in the higher energy range. Conversely, they demonstrate transparency to incident photons in the lower energy range. Based on our analysis of the optical properties, we have determined that these compounds are well-suited for applications in high-frequency UV devices. To the best of our knowledge, this study represents the first comprehensive theoretical analysis of the structural, elastic, electronic, and optical properties of Cs2YXCl6 (X = In and Tl), which have not yet been experimentally confirmed. In Summary, Cs2YXCl6 (X = In, Tl) exhibits significant promise for both solar cell and thermoelectric applications, showcasing its potential to contribute to the advancement of renewable energy and efficient energy conversion technologies.

Enhancing the performance of the solar thermoelectric generator in unconcentrated and concentrated light

The solar thermoelectric generator is undoubtedly an important candidate to convert solar into electric energy. The current efficiency of the thermoelectric generator is low, but recent research indicates an improvement in efficiency. The paper presents a method that leads to performance enhancement of the solar thermoelectric generator. An absorbent layer comprising of metallic oxides and additives was deposited by the spray deposition technique on the hot side of the solar thermoelectric generator to increase irradiance absorption. The main properties of the absorbent layer consist of an optimized IR absorption, good thermal transmission to the contact material, and thermal resistance. The absorbent layer deposited on the hot side of the STEG has low thermal emittance 0.073, high absorbance 0.98 and high stability, which makes it a very good candidate for use as an absorbent layer for improving the performance of the STEG. The new solar thermoelectric generator is studied in two environmental situations: artificial light in the lab, from 600 W/m2 to 1200 W/m2 and in concentrated light from 20 suns to 80 suns. Analysis of the results obtained shows an increase in power generation more than 25 % for the irradiance around 1 sun and up to 82 % for the concentration light.

Stretchable photothermal membrane of NIR-II charge-transfer cocrystal for wearable solar thermoelectric power generation

Harvesting sunlight into cost-effective electricity presents an enticing prospect for self-powered wearable applications. The photothermal materials with an extensive absorption are fundamental to achieve optical and thermal concentration of the sunlight for efficiency output electricity of wearable solar thermoelectric generators (STEGs). Here, we synthesize an organic charge-transfer (CT) cocrystal with a flat absorption from ultraviolet to second near-infrared region (200 to 1950 nanometers) and a high photothermal conversion efficiency (PCE) of 80.5%, which is introduced into polyurethane toward large-area nanofiber membrane by electrospinning technology. These corresponding membranes demonstrate a high PCE of 73.7% under the strain more than 80%. Sandwiched with carbon nanotube–based thermoelectric fibers, the membranes as stretchable solar absorbers of STEGs could supply a notably increase temperature gradient, processing a maximum output voltage density of 23.4 volts per square meter at 1:00 p.m. under sunlight. This strategy presents an important insight in heat management for wearable STEGs with a desired electricity output.