These researchers have created a new system to artificially capture light and convert it into power, thus recreating photosynthesis, the process by which plants absorb sunlight and produce sugar. This could potentially change how we collect solar energy.
Scientists worldwide have attempted to create more efficient solar cells by replicating chromophores' molecular and atomic structure — light-absorbing molecules used by plants in photosynthesis — in lab-engineered systems.
Chromophores absorb visible light and transfer it to other components, which use the energy for various chemical reactions. The exposed chromophores on leaves absorb solar energy and transfer it to neighbouring chromophores until it reaches its destination.
However, these attempts using polymeric structures, detergent-type molecules, and other similar structures have all encountered a common problem: molecular bunching or aggregation, which results in poor light capture and conversion efficiencies. Because aggregation reduces the active sites on molecules, it reduces their activity and ability to harvest light. As a result, this aggregation results in less efficient light absorption.
"Understanding the structure of these nanoclusters is critical for finding ways to improve their efficiency." Previously, the silver nanoclusters had fragile emission properties at room temperature. We were able to improve its emission properties by strategically synthesising them, improving the way it captures, absorbs, and transfers light between molecules," said Dr. Sukhendu Mandal, Associate Professor, Department of Chemistry, IISER.
The researchers discovered a method to create a highly efficient photosynthetic system using silver nanoclusters a hundred thousand times smaller than the width of human hair due to this study. The scientists used organic adamantanethiol ligands to react with and surround the inorganic silver molecules, protecting them from the environment and preventing them from reacting with each other and other substances. Ligands are neutral molecules or ions that form bonds with a central metal atom or ion.
This ligand-protected molecule is then entrapped inside another large molecule known as cyclodextrin, which further protects the silver nanoclusters, increasing their longevity and improving their emission properties. The scientists achieved a 93% energy transfer efficiency using this method, demonstrating that the harvested energy could generate current with significantly higher yields than the individual components.
"We used silver clusters because they are less expensive than gold and platinum clusters." However, using silver presented some difficulties because the material is prone to oxidation and is light sensitive," explained Dr. Mandal of IISER, TVM. "To overcome these challenges with silver, we used organic ligands to protect the silver clusters from oxidation and worked on it at night to avoid any reaction with light," said the project's lead researcher. “The clusters were protected by entrapment in the cyclodextrin molecule, which also increased their longevity and improved their emission properties."
The researchers hope that their research into highly efficient energy transfer systems will lay the groundwork for developing new light-harvesting materials that will improve the efficiency of solar cells and reduce energy loss. "In this project, we are also working with copper clusters because it is the cheapest material, and we want to make this technology as cost-effective as possible. However, because copper oxidizes faster than silver, it poses a greater challenge," Dr. Mandal explained.
IISER, TVM's Dr. Sukhendu Mandal, Dr. Sourav Biswas, Anish Kumar Das, and IIT Indore's Professor Biswarup Pathak and Surya Sekhar Manna all contributed to the paper. These studies are expected to contribute to India reaching net-zero carbon emissions by 2070 and meeting 50% of its electricity needs through renewable sources such as solar power by 2030.
