Low-grade heat (below 373 K) is abundant and ubiquitous, but mostly wasted due to the lack of cost-effective recovery technologies. The liquid-state thermocell (LTC), an inexpensive and scalable thermoelectric device, may be commercially viable for harvesting low-grade heat energy if its Carnot-relative efficiency (ηr) reaches ~5%, which is a challenging metric to achieve experimentally. We used a thermosensitive crystallization and dissolution process to induce persistent concentration gradient of redox ions, a highly enhanced Seebeck coefficient (~3.73 mV K–1), and suppressed thermal conductivity in LTCs. As a result, we achieved a high ηr of 11% for LTCs near room temperature, and a substantially decreased cost-performance of our LTC. Our device demonstration offers promise for cost-effective low-grade heat harvesting.

https://science.sciencemag.org/content/sci/370/6514/342.full.pdf

Thermosensitive crystallization-boosted liquid thermocells for low-grade heat harvesting.

To develop photosensitizers with high open-circuit photovoltage (Voc) is a crucial strategy to enhance the power conversion efficiency (PCE) of co-sensitized solar cells. Here, we show a judiciously tailored organic photosensitizer, coded MS5, featuring the bulky donor N-(2’,4’-bis(dodecyloxy)-[1,1’-biphenyl]-4-yl)-2’,4’-bis(dodecyloxy)-N-phenyl-[1,1’-biphenyl]-4-amine and the electron acceptor 4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid. Employing MS5 with a copper (II/I) electrolyte enables a dye-sensitized solar cell (DSC) to achieve a strikingly high Voc of 1.24 V, with the Voc deficit as low as 130 mV and an ideality factor of merely 1.08. The co-sensitization of MS5 with the wider spectral-response dye XY1b produces a highly efficient and stable DSC with the PCE of 13.5% under standard AM1.5 G, 100 mW cm−2 solar radiation. Remarkably, the co-sensitized solar cell (active area of 2.8 cm2) presents a record PCE of 34.5% under ambient light, rendering it very attractive as an ambient light harvesting energy source for low power electronics. Designing photo-sensitisers with high open-circuit voltage (Voc) is desirable to enhance the power conversion efficiency (PCE) of co-sensitized solar cells. Here, the authors employ a judiciously tailored organic sensitiser MS5 with copper electrolyte to achieve a Voc of 1.24 V, and recorded PCE of 34.5% under ambient light.

/pdf/a-molecular-photosensitizer-achieves-a-v-oc-of-1-24-v-1y8sly3gp9.pdf

A molecular photosensitizer achieves a V oc of 1.24 V enabling highly efficient and stable dye-sensitized solar cells with copper(II/I)-based electrolyte

Recent progress of organic photovoltaics for indoor energy harvesting

With the growing development of the Internet of Things, organic photovoltaic (OPV) cells are highly desirable for indoor applications because of the unique features of light weight, flexibility, and coloration. Emission spectra of the commonly used indoor light sources are much narrower with lower light intensity as compared to the standard solar spectrum. High tunability in optical absorption, insensitivity to series resistance and the active layer thickness, and mild operating conditions make indoor OPV cells promising as a practically relevant technology. Currently, the OPV module has obtained a power conversion efficiency of over 20%, with excellent stability under indoor conditions. However, at the present stage, the device physics investigations and material design strategies developed in an OPV cell for indoor applications lag behind those for outdoor applications. In particular, the emerging characterizations in photovoltaic measurements have severely affected the reliability of reports. This Spotlight on Applications highlights these opportunities and challenges of OPV cells for indoor applications and reviews the recent progress in indoor OPV cells. In addition, we summarize some studies related to accurate measurement and provide some recommendations.

Organic Photovoltaic Cells for Indoor Applications: Opportunities and Challenges.

Mechanisms and Suppression of Photoinduced Degradation in Perovskite Solar Cells

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.201901980

Tailoring Triple‐Anion Perovskite Material for Indoor Light Harvesting with Restrained Halide Segregation and Record High Efficiency Beyond 36%

Efficient low-grade heat recovery can help to reduce greenhouse gas emission as over 70% of primary energy input is wasted as heat, but current technologies to fulfill the heat-to-electricity conversion are still far from optimum. Here we report a direct thermal charging cell, using asymmetric electrodes of a graphene oxide/platinum nanoparticles cathode and a polyaniline anode in Fe2+/Fe3+ redox electrolyte via isothermal heating operation. When heated, the cell generates voltage via a temperature-induced pseudocapacitive effect of graphene oxide and a thermogalvanic effect of Fe2+/Fe3+, and then discharges continuously by oxidizing polyaniline and reducing Fe3+ under isothermal heating till Fe3+ depletion. The cell can be self-regenerated when cooled down. Direct thermal charging cells attain a temperature coefficient of 5.0 mV K−1 and heat-to-electricity conversion efficiency of 2.8% at 70 °C (21.4% of Carnot efficiency) and 3.52% at 90 °C (19.7% of Carnot efficiency), outperforming other thermoelectrochemical and thermoelectric systems. Recovery of low-grade heat can aid in reducing greenhouse gas emissions, but heat-to-electricity conversion technologies should be optimized. Here the authors report a direct thermal charging cell that uses asymmetric electrodes and a redox electrolyte to efficiently convert low-grade heat into electricity.

/pdf/direct-thermal-charging-cell-for-converting-low-grade-heat-5a1vrf701t.pdf

Direct thermal charging cell for converting low-grade heat to electricity.

Solution-processed 2D organic semiconductors (OSCs) have drawn considerable attention because of their novel applications from flexible optoelectronics to biosensors. However, obtaining well-oriented sheets of 2D organic materials with low defect density still poses a challenge. Here, a highly crystallized 2,9-didecyldinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (C10-DNTT) monolayer crystal with large-area uniformity is obtained by an ultraslow shearing (USS) method and its growth pattern shows a kinetic Wulff's construction supported by theoretical calculations of surface energies. The resulting seamless and highly crystalline monolayers are then used as templates for thermally depositing another C10-DNTT ultrathin top-up film. The organic thin films deposited by this hybrid approach show an interesting coherence structure with a copied molecular orientation of the templating crystal. The organic field-effect transistors developed by these hybrid C10-DNTT films exhibit improved carrier mobility of 14.7 cm2 V-1 s-1 as compared with 7.3 cm2 V-1 s-1 achieved by pure thermal evaporation (100% improvement) and 2.8 cm2 V-1 s-1 achieved by solution sheared monolayer C10-DNTT. This work establishes a simple yet effective approach for fabricating high-performance and low-cost electronics on a large scale.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/advs.201900775

Field‐Effect Transistors Based on 2D Organic Semiconductors Developed by a Hybrid Deposition Method

/pdf/orientation-engineered-small-molecule-semiconductors-as-1jgg0x13b3.pdf

Orientation-Engineered Small-Molecule Semiconductors as Dopant-Free Hole Transporting Materials for Efficient and Stable Perovskite Solar Cells

The thermally regenerative electrochemical cycle (TREC) is a promising technology for converting low-grade heat (<100 °C) to electrical power. In this work, the TREC with the NiHCF cathode and Zn a...

Sijia Wang

Papers

Tailoring Triple‐Anion Perovskite Material for Indoor Light Harvesting with Restrained Halide Segregation and Record High Efficiency Beyond 36%

Direct thermal charging cell for converting low-grade heat to electricity.

Field‐Effect Transistors Based on 2D Organic Semiconductors Developed by a Hybrid Deposition Method

Orientation-Engineered Small-Molecule Semiconductors as Dopant-Free Hole Transporting Materials for Efficient and Stable Perovskite Solar Cells

Insights into the Thermopower of Thermally Regenerative Electrochemical Cycle for Low Grade Heat Harvesting