The evolution of green energy technology: Developing three-dimensional smart energy devices with radiant cooling and solar absorption
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Advanced Materials Cover
view moreCredit: Advanced Materials Cover
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A research team led by Professor Bonghoon Kim from DGIST’s Department of Robotics and Mechatronics Engineering has developed a “3D Smart Energy Device” that features both reversible heating and cooling capabilities. The team collaborated with Professor Bongjae Lee from KAIST’s Department of Mechanical Engineering and Professor Heon Lee from Korea University’s Department of Materials Science and Engineering. Their innovative device was officially recognized for its excellence and practicality through its selection as the cover article of the international journal Advanced Materials.
□ Heating and cooling account for approximately 50% of the global energy consumption, contributing significantly to environmental problems such as global warming and air pollution. In response, solar absorption and radiative cooling devices, which harness the sun and outdoor air as heat and cold sources, are gaining attention as eco-friendly and sustainable solutions. While various devices have been developed, many are limited in function, focusing solely on heating or cooling, and large-scale systems lack adjustability.
□ To address these limitations, Prof. Kim’s team created a “3D Smart Energy Device” that integrates reversible heating and cooling functions in a single device. The device operates on a unique mechanism: when the 3D structure opens through a mechanical peeling process, the lower layer—made of silicone elastomer and silver—is exposed to generate radiative cooling. When the structure closes, the surface coated with black paint absorbs solar heat, thus producing heating.
□ The team tested the device on multiple substrates, including skin, glass, steel, aluminum, copper, and polyimide, and demonstrated that adjusting the angle of the 3D structure enabled control over its heating and cooling performance. This ability to modulate thermal properties offers an efficient and promising solution for reducing energy consumption in temperature-controlled buildings and electronic devices at both macro and micro scales.
□ “We are honored to have our research selected for the cover article of such a prestigious journal,” said Professor Bonghoon Kim. “We aim to ensure that these findings are applied in industrial and building settings to help reduce energy consumption.”
□ This research was supported by the “Global Bioconvergence Interfacing Leading Research Center (ERC)” and the “Nano and Materials Technology Development Project” of the National Research Foundation of Korea. The results were published in Advanced Materials, where they were featured as the cover article.
- Corresponding Author E-mail Address : bonghoonkim@dgist.ac.kr
Journal
Advanced Materials
Article Title
Reversible Solar Heating and Radiative Cooling Devices via Mechanically Guided Assembly of 3D Macro/Microstructures
Next-generation solar cells become more powerful with silver (Ag) doping technology!
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A team of senior researchers, including Kee-jeong Yang, Dae-hwan Kim, and Jin-gyu Kang from the Division of Energy & Environmental Technology, DGIST (President Kunwoo Lee), collaborated with Prof. Kim Jun-ho’s team from the Department of Physics, Incheon National University and Prof. Koo Sang-mo’s team from the Department of Electronic Materials Engineering to significantly improve the performance of kesterite (CZTSSe) thin-film solar cells in joint research. They developed a new method for doping silver (Ag) in solar cells to suppress defects that hinder cell performance and promote crystal growth, thereby dramatically increasing efficiency and paving the way for commercialization.
□ CZTSSe solar cells are composed of copper (Cu), zinc (Zn), tin (Sn), sulfur (S), and selenium (Se), and are gaining attention as a resource-abundant, low-cost, and eco-friendly solar cell technology. In particular, they have the advantage of being suitable for large-scale production and highly competitive in price because they use materials that are abundant in resources instead of the scarce metals used in conventional solar cells. However, conventional CZTSSe solar cells have low efficiency and high current losses due to electron-hole recombination, thus making them difficult to commercialize.
□ To address these issues, the research team employed a method of doping the solar cell precursor with Ag. Ag inhibits the loss of Sn and helps the materials mix better at low temperatures. This allows the crystals to grow larger and faster, reducing defects and improving the performance of the solar cell. In this study, they systematically analyzed how the placement of Ag at different locations in the precursor changes the defects and electron-hole recombination properties in the solar cell. The results indicate that Ag can significantly improve the performance of the solar cell by preventing Sn loss and maximizing the defect suppression effect.
□ Importantly, they also found that doping Ag in the wrong place actually interferes with the formation of Zn and Cu alloy, causing Zn to remain in the bulk and form defect clusters. This can lead to increased electron-hole recombination losses and degraded performance. From this, the research team offered an important insight: solar cell performance varies significantly depending on where Ag doping occurs.
□ Furthermore, the research team found that the liquid material formed by Ag doping promotes crystal growth, significantly improving the density and crystallinity of the absorber layer. This resulted in an improved energy band structure and fewer defects, ultimately allowing for smoother charge transport in the cell. These findings are expected to contribute significantly to the production of high-performance solar cells at low cost.
□ “In this study, we analyzed the effect of Ag doping, which had not been clearly identified before, process by process, and found that silver plays a role in suppressing tin loss and improving defects,” said Yang Kee-jeong, a senior researcher at the Division of Energy & Environmental Technology. “The results provide important insights into the design of silver-doped precursor structures to improve solar cell efficiency and are expected to contribute to the development of various solar cell technologies.”
□ The research was funded by the Ministry of Science and ICT’s Source Technology Development (Leapfrog Development of Carbon Neutral Technology) Program and the Future-Leading Specialization Research (Grand Challenge Research and Innovation Project (P-CoE)) Program. The paper was published online in the Energy & Environmental Energy (IF 32.4), a leading international journal in the field of energy.
- Corresponding Author E-mail Address : kjyang@dgist.ac.kr
Journal
Energy & Environmental Science
Article Title
Reducing carrier recombination loss by suppressing Sn loss and defect formation via Ag doping in Cu2ZnSn(S,Se)4 solar cells
New performance record for eco-friendly nanocrystal solar cells
ICFO-The Institute of Photonic Sciences
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Schematic of the post-deposition in situ passivation strategy on the AgBiS2 nanocrystal. Source: EES.
view moreCredit: EES
In the era of climate change, renewable energies have quickly gained popularity, with solar cells being a prominent example of this shift. For instance, in 2023, installed solar photovoltaic power increased by 28% in Spain compared to the previous year, accounting for 20.3% of Spain’s total energy generation pool, a trend that is similarly mirrored in most Western countries. Despite their commercialization and their unquestionable environmental benefits, solar cells still have room for improvement, as they are usually based on materials that are not fully sustainable. Ubiquitous solar harvesting – beyond solar farms - is considered the way to go to power buildings, infrastructures, IoT systems or even vehicles. That would require light-weight, low cost, flexible and eco-friendly based solar cell technology. The scientific community is thus directing its efforts toward finding sustainable alternatives that preserve (or even boost) the electricity generation efficiency, reduce costs and simplify the manufacturing efforts of current solar cells.
One promising material that has emerged as an environmentally-friendly alternative is colloidal silver bismuth sulfide (AgBiS2) nanocrystal, a material that is characterized by an extremely high absorption coefficient and thus leads toultra-thin-film absorbers for solar cells. Through a layer-by-layer manufacturing process, solar cells with compelling performance have already been reported. But to minimize material loss, reduce costs and improve manufacturing scalability, the multi-step deposition method must be replaced by a single-step approach.
This can be realized by developing AgBiS2 nanocrystal inks. Since 2020, several researches in this regard have been reported. However, the resulting AgBiS2 nanocrystals have still exhibited significant surface defects accompanied by low power conversion efficiency in a solar cell, meaning that the techniques aimed at eliminating them -called surface passivation- were not sufficiently effective. The remaining surface defects trapped the electrical charge carriers generated by sunlight and triggered their recombination, reducing the device efficiency to lower levels than those achieved with a layer-by-layer manufacturing procedure.
Therefore, a simpler yet more effective passivation methodology for AgBiS2 nanocrystal ink is needed to bring the efficiency of eco-friendly solar cells closer to competitive levels. Recently, ICFO researchers, Dr. Jae Taek Oh, Dr. Yongjie Wang, Dr. Carmelita Rodà, Dr. Debranjan Mandal, Dr. Gaurav Kumar, Dr. Guy Luke Whitworth, led by ICREA Prof. Gerasimos Konstantatos, have taken a significant step forward in this direction. In an Energy & Environmental Science article, they have reported on a post-deposition in situ passivation (P-DIP) strategy that improves surface passivation, yielding nanocrystal ink films with enhanced optoelectronic properties. The resulting ultrathin solar cells showed higher power conversion efficiency than their multi-step deposition counterparts, setting a new performance record for eco-friendly nanocrystal solar cells.
Post-deposition in situ passivation for improved surface passivation
ICFO researchers managed to effectively passivate surface defects present in their nanocrystal ink film. “Imagine a bumpy road that slows down cars. Surface passivation is like repaving the road, making it smoother so cars can move without getting stuck. In our case, the removal of surface defects is very important to facilitate the transportation of charge carriers created from light absorption in nanocrystal films”, explains Dr. Jae Taek Oh, first author of the article. “With our P-DIP method, charge carries could move without ‘bumping into so many obstacles’ within the AgBiS2 nanocrystals thin film”, he adds.
The mitigation of defects by a proper passivation strategy translated into higher film quality and, thus, higher performance solar cells. Their efficiency of around 10% exceeded that of previous solar cells based on AgBiS2 nanocrystals, involving both single-step and layer-by-layer deposition methods.
To obtain these outstanding results, the team synthesized the AgBiS2 nanocrystal ink by introducing a multifunctional molecular agent containing chlorine. Its molecular structure helped stabilize the nanocrystals and disperse them evenly within the solution, two crucial factors to ensure smooth coatings. After depositing the film, they carried out additional passivation on the surfaces of AgBiS2 nanocrystals. This particular in situ passivation strategy extended the carrier lifetime and balanced carrier transport in the film, which are also critical aspects to enhance the efficiency of solar cells. The combination of these effects was the perfect recipe to achieve the unprecedented performance for sustainable solar cells that ICFO researchers have demonstrated in this study.
Schematic of the post-deposition in situ passivation strategy on the AgBiS2 nanocrystal. Source: EES. (IMAGE)
Schematic of the post-deposition in situ passivation strategy on the AgBiS2 nanocrystal. Source: EES.
Credit
EES
Reference:
J. T. Oh, Y. Wang, C. Rodà, D. Mandal, G. Kumar, G. L. Whitworth, G. Konstantatos. Energy Environ. Sci. (2024). DOI: https://doi.org/10.1039/D4EE03266G
Journal
Energy & Environmental Science
Article Title
Post-deposition in situ passivation of AgBiS2 nanocrystal inks for high-efficiency ultra-thin solar cells
Thermophotovoltaics demonstrate economic promise
Analysis reveals thermophotovoltaics' potential for cost-effective energy generation, highlighting key factors influencing economic feasibility
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Converting heat to electrical power, TPV combines a thermal emitter and a photovoltaic cell.
view moreCredit: M. Mosalpuri et al., doi 10.1117/1.JPE.14.042404.
As the world shifts towards sustainable energy solutions, researchers are exploring innovative technologies that can efficiently convert heat into electricity. One such technology, thermophotovoltaics (TPV), utilizes heat from thermal emitters to generate power through specially designed photovoltaic cells. TPV systems are gaining attention for their ability to produce energy silently and without moving parts, making them low-maintenance and potentially cost-effective. A recent study, reported in Journal of Photonics for Energy, provides insights into the economic feasibility of TPV integrated with solar energy and storage systems, highlighting its promise for future energy applications.
The study conducted a thorough techno-economic analysis of a TPV system paired with phase-change materials for energy storage. Researchers used an optimization method to assess the levelized cost of consumed energy (LCOE) and the levelized cost of electricity (LCOEel) across four different scenarios for a typical residential building in Boone, Iowa. These scenarios were distinguished by variations in key financial factors such as the cost of capital, inflation rates for fuel and electricity, and the capital costs associated with high-temperature energy storage and power generation systems.
The findings revealed a slight reduction in both LCOE and LCOEel, from initial estimates of $0.038 per kilowatt-hour and $0.128 per kilowatt-hour, respectively. This analysis also included a Monte Carlo uncertainty assessment, which examined how different variables could influence these costs over time. The results suggested that while TPV technology holds significant economic potential, the LCOEel currently exceeds the average electricity price.
The study identified several critical factors that affect the overall cost of TPV systems, including system lifetime, capital costs, inflation rates, and the price of natural gas. By focusing future research on these areas, scientists hope to improve the adoption of TPV technology, lighting the way for more efficient and sustainable energy systems.
For details, see the original article by M. Mosalpuri et al., “Techno-economic analysis of a solar thermophotovoltaic system for a residential building,” J. Photon. Energy 14(4), 042404 (2024), doi 10.1117/1.JPE.14.042404.
Journal
Journal of Photonics for Energy
Article Title
Techno-economic analysis of a solar thermophotovoltaic system for a residential building
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