“Revolutionary Nanocrystal Breakthrough Maximizes Solar Energy Harvesting from Infrared Light”

In the quest for sustainable energy sources, scientists have made significant strides in harnessing solar power. However, current solar technology predominantly relies on visible and ultraviolet rays, leaving a vast portion of the solar spectrum untapped. Researchers from Hokkaido University, led by Assistant Professor Melbert Jeem and Professor Seiichi Watanabe, have unveiled a groundbreaking discovery that could revolutionize solar energy generation. Their findings, published in the journal Advanced Materials, center around copper-doped tungstic acid nanocrystals capable of harnessing the full spectrum of solar radiation, including the often-overlooked infrared range.

Assistant Professor Jeem elaborates, “Presently, solar technology neglects the potential energy within the near- and mid-infrared spectra, spanning from 800 nm to 2500 nm. Tungstic acid, with its crystal structure featuring inherent defects that absorb these wavelengths, emerges as a promising candidate for nanomaterial development capable of utilizing this untapped solar resource.”

The research team employed a sophisticated photo-fabrication technique, previously developed, known as “submerged photo-synthesis of crystallites,” to create copper-doped tungstic acid nanocrystals with varying copper concentrations. These nanocrystals were subjected to extensive analysis, evaluating their structural characteristics and light-absorbing properties. Moreover, their performance in terms of photothermal effects, photo-assisted water evaporation, and photo-electrochemical behavior was meticulously assessed.

Remarkably, the copper-doped tungsten oxide nanocrystals exhibited a remarkable ability to absorb light across the entire solar spectrum, ranging from ultraviolet through visible light to infrared. Among the various copper concentrations tested, the 1% copper-doped nanocrystals exhibited the highest absorption of infrared light. Furthermore, these 1% and 5% copper-doped nanocrystals demonstrated the most significant temperature elevation (photothermal characteristic), while the 1% copper-doped crystals excelled in water evaporation efficiency, reaching approximately 1.0 kg per m² per hour. Structural analysis indicated that the presence of copper ions might distort the tungsten oxide crystal structure, leading to the observed characteristics upon light absorption.

Professor Watanabe underscores the significance of their findings, stating, “Our discoveries represent a substantial leap in the development of nanocrystals capable of both generating and harnessing solar energy across the entire spectrum. Copper doping imparts diverse characteristics to tungstic acid nanocrystals, enabling all-solar utilization. This breakthrough provides a solid foundation for further research and potential applications.”

This pioneering research, titled “Defect Driven Opto-Critical Phases Tuned for All-Solar Utilization,” authored by Melbert Jeem, Ayaka Hayano, Hiroto Miyashita, Mahiro Nishimura, Kohei Fukuroi, Hsueh-I Lin, Lihua Zhang, and Seiichi Watanabe, was published on July 29, 2023, in Advanced Materials. The project received support from the Japan Society for the Promotion of Science (JSPS) KAKENHI (20H00295, 21K04823) and benefited from the advanced research infrastructure for materials and nanotechnology in Japan (ARIM), sponsored by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT).

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• Advanced Materials Journal
• Hokkaido University
• Japan Society for the Promotion of Science (JSPS) KAKENHI
• Ministry of Education, Culture, Sports, Science and Technology (MEXT)