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New Nano-structure Is Developed to Raise Light Energy Conversion Efficiency

published: 2018-01-02 16:44

A group of nano-scientists found a newer, faster, and better energy conversion method. They created a type of hybrid nano-material that can accelerate the conversion of light energy to hot electron, so as to raise solar energy efficiency. This is a great improvement to related PV technologies.

This nano-material is only 10-9m long and developed by the team from Department of Energy's Argonne National Laboratory from the US. It can utilize all the energy from a photon.

Typically, in bigger particles, there are very few hot electrons whose energies are approaching photons' energy level while hot electrons are with extremely high momentum. Thus, nano-scientists needed the help from smaller particles. Then researchers adjusted the metals and metal nano-structures that are responsible to absorb light. This is the first step to escalate the amount of energetic electrons. 

In order to find out which hybrid nano-materials can generate the most number of hot electrons, researchers tried lots of combinations. At the end, they declared the winner to be silver nano-cubes and gold films that are separated by Al2O3 (aluminium oxide) spacer. The coupling of these two can enhance the energy of light. One of the critical reasons is that, when compared with other structures, this nano-structure can generate more hot electrons from a broader range of spectrum (from ultra-violet, the visible, to the near infra-red).

The research team used the transient absorption spectrometer to measure the change rate in the concentration of hot electrons. The result can determine when and how hot electrons will lose energy. In this way, the result helped researchers find out a clue of how to reduce energy loss or a method to extract the hot electrons before they lose energies.

Moreover, this nano-structure contains different bands of energy. These bands will influence the decay rate of the hot electrons when electrons move within these bands. Hence, different electrons' lifespan will be different. Each electron's lifetime length will depend on the direction of the electron. Matthew Sykes, one of the co-authors of the thesis, said that it would be helpful to imagine that some electrons are vehicles that are moving on the freeway. If the traffic is light, then electrons can keep higher speed for a longer time. By contrast, if some electrons unfortunately encounter busy traffic during the rush hour, then they are forced to slow down. This factor above will determine how long a hot electron can survive after being activated.

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