Multi-Institutional team led by IISER Thiruvananthapuram develops highly efficient Artificial Photosynthetic systems for Solar energy capture

Thiruvananthapuram : Researchers from Indian Institute of Science Education and Research (IISER) Thiruvananthapuram and IIT Indore have studied and developed a new artificial light-harvesting system that can efficiently capture light for power conversion by mimicking photosynthesis, the process by which plants absorb sunlight and produce sugars. The results of this study have been published in the journal of the prestigious Royal Chemical Society – Chemical Science. The paper has been co-authored by IISER TVM researchers – Dr. Sukhendu Mandal, Associate Professor, Department of Chemistry along with his research scholars Dr. Sourav Biswas and Mr. Anish Kumar Das, and IIT Indore researchers – Prof. Biswarup Pathak, Department of Chemistry, IIT Indore, along with this research scholar Mr. Surya Sekhar Manna.

All over the world, scientists are trying to replicate the light-harvesting step of photosynthesis in engineered systems for use in solar cells or artificial leaves. The light-harvesting cores in plants and other photosynthetic bacteria are chromophores, molecules that absorb visible light and pass it on to other components that use the energy for various chemical reactions. The top most chromophores that are exposed to the sun absorb the energy. The chromophores are arranged in arrays and an energised chromophore passes the energy to the adjoining chromophore, and so on. There is a rapid cascade of energy until the energy reaches its destination.

There have been many attempts at replicating the molecular and atomic structure of the light-harvesting mechanism in the lab. Polymeric structures, detergent-type molecules, vesicles, gels, and other bioinspired structures have been used to mimic photosynthesis. The most common problem faced by such molecules is that the light is quenched due to aggregation or bunching up of the molecules together. This leads to poor light capture and conversion efficiencies.

The IISER TVM and IIT Indore scientists have found a way to overcome the quenching problems of artificial light absorbers and transmitters. They have worked with clusters of silver that are of nanometer dimensions – a hundred thousand times smaller than the width of human hair. Such nanoclusters have fascinating structures and exotic photophysical properties. The researchers stabilised these nanoclusters with bulky ligands and entrapped the entire ensemble inside another large molecule called cyclodextrin.

Explaining the structure of their atomically precise molecule, Dr Sukhendu Mandal, Associate Professor, Department of Chemistry, IISER TVM, said “The molecule we developed is a 16 silver atoms-ligand-cyclodextrin assembly that acts as a donor and β-carotene as an acceptor. This is the first time we have utilized atom-precise nanocluster in such an application”.

Explaining further, the lead researcher said, “The opposite charges on the surfaces and the matched electronic energy distribution result in a 93% energy transfer efficiency with a great antenna effect from the UV-to-visible region of the light spectrum”. The researchers also showed that this harvested energy could generate current with much-enhanced yields compared to the individual components.

The IISER TVM and IIT Indore researchers believe that this fundamental investigation into highly-efficient energy transfer systems will provide the basis for designing new light-harvesting materials that can enhance the efficiency of solar cells and reduce energy loss. This is important given that India aims to achieve net zero carbon emissions by 2070 and to meet 50% of its electricity needs from renewable sources such as solar power by 2030.

The researchers believe that although there is a long way to go to ensure that these types of materials enter mainstream solar energy generation on a mass scale, such research help in bringing efficiency enhancement one step closer to reality.