Solar Cell Technology: What is the Latest Breakthrough? - WorldOfChemicals

Excited State! - A Breakthrough In Solar Cell Technology

Category : General Chemicals
Published by : Data Research Analyst, Worldofchemicals.com

Solar cells in the past had a limit on their efficiency. In a conventional silicon based solar cell, each light photon that would strike the surface of the cell would release one electron. Photons with greater energy would not make a difference as they could not draw additional electrons. Researchers have now come up with a novel method to obtain high energy light photons to release two electrons instead of one, which opens avenues for a new type of solar cell with greater efficiency.


The highest possible theoretical efficiency achieved by conventional solar cells are 29.1%. Over the last few years, researchers at MIT and other places have developed a new method to increase the efficiency of the cells.


Early Demonstrations

The principle of this technology has been known as well as its demonstration has already been carried out. However, it took years for this technology to become operational. Earlier studies demonstrated the release of two electrons from one light photon for organic photovoltaic cells. However, silicon solar cells are more efficient than organic solar cells. When tests were conducted on a solar cell with the top layer being composed of tetracene, the transfer of two electron was not straightforward. Although, this technology was conceptualized 4 decades back, its practicality is now becoming a reality.

 

Excitation Process

The technology involves the use of excitons, which are a group of materials that contain excited states. They enable the energy division of one photon into two electrons. Excitons are packets of energy like electrons which propagate in a circuit. However, they have different properties as compared with electrons. In this process, singlet exciton fission is carried out, where light energy gets split into two independent mobile packets of energy. Silicon solar cell absorbs a photon and forms an exciton, which undergoes fission reaction to form two excited states, where each packet of energy possesses half the energy of the initial state.


Resolving Challenges 

Coupling the energy obtained from photon into silicon was difficult as it is a non-excitonic material. The research team tried to couple the energy from the excitonic layer into tiny semiconductor particles known as quantum dots. This was when the breakthrough happened in solar cell technology, where they were both inorganic and excitonic. This led to the development of a more efficient silicon solar cell.


Role of Surface Chemistry

The energy transfers are possible not due to the bulk of the material but due to the surface of the material. The research team were able to obtain the desired results due to their focus on the surface chemistry of silicon. This helped in the determination of the surface states that were present there. The solution lies in a thin intermediate layer, which is at the interface between the tetracene layer and the silicon cell layer. The intermediate material used is hafnium oxynitride, which is a few atoms thick and acts as bridge for the excitons. This new technology pushed the maximum theoretical efficiency from 29.1% to 35%.


Scope 

Although, efficient coupling of the two materials has been accomplished, further optimization of silicon cells is required for this process. There is a need for the cells to be made thinner than the present versions. Stabilization of materials for durability must also be worked upon. It would take few years for the product to be commercially available. Other methods to improve efficiency involve addition of other types of cells like perovskite layer over silicon.


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