Debasmita Banerjee
Debasmita Banerjee
Instrumentation
25 Jan 2016

Controlling Electrons At Femtosecond Timescales Could Enhance Efficiency Of Solar Cells

A group of physicists at MIT has developed a way to manipulate electron-light interaction in conducting sheets which may potentially upgrade the performance of solar cells. With this innovation, scientists can redirect highly-energized electrons before they interact with other electrons. The findings of this research were published in 'Nature Physics' under the title “Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure.”

By default, electrons tend to settle in the low-energy band if no external stimulation is given, so that atoms maintain their stability. If light is incident on the electrons, it jumps to high energy states resulting in a series of interactions within a femtosecond (10^-15 seconds). These energized electrons scatter and affect other electrons to finally reach thermal equilibrium by distributing the energy, a process dubbed as thermalization.

electron_burst
The middle "explosion" is a cloud of hot electrons

The department of Physics at MIT has devised an ultrafast control of high-energy electrons on a conducting surface like silicon or graphene that may lead to more efficient photovoltaic cells, a way to capture photo-excited electrons before they lose their energy to thermalization.

Jarillo-Herrero, the team leader explained that the idea behind their research generated from the results of their previous experiment. Owing to extremely short time and length scales, controlling, measuring and manipulating electron thermalization in nanoscale devices remains a very difficult task. Ma, a member of the group explained that the high speed interaction appears due to the one-atom thick 2-D structure of graphene.

graphene_channel

The team finally concluded that coaxing electrons to jump from one sheet of graphene to another required perfect sync between the voltage and light energy. Recording the pattern from a series of voltages and light they could ultimately reproduce a method for controlling the electrons before they stabilize.

Jarillo-Herrero claimed that their research could potentially improve efficiency in photovoltaic devices. In general, if the light consists of lower-energy infrared photons, silicon does not absorb them, and this limits the efficiency of solar cells. The future goal of the Herrero team is to practically incorporate the process into optoelectronic devices.

Watch Thermilization of Silicon Nano-wire -


Source: MIT News | Nature Physics

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