Study to Help Develop More Efficient Solar Cells

Many technical applications, such as the development of solar cells or new types of electronic components need a mapping of the dynamics of electrons in molecules and solids as exactly as possible.

Modern microscopy methods offer almost unlimited possibilities to perform the task. However, they are all also associated with certain limitations or others. For instance, scanning tunneling microscopy, which has a resolution of a tenth of a picometer (a picometer is a trillionth of a meter) allows taking extremely sharp images of individual atoms. But it is slow and, therefore, cannot capture the dynamics of the electrons in a material. Likewise, optical methods with ultrafast laser pulses can detect electron movements at ultra-high speed, in the attosecond range (an attosecond is one billionth of a billionth of a second). But they cannot deliver clear images simultaneously.

A research group at the Max Planck Institute for Solid State Research headed by an Indian scientist, Dr. Manish Garg, has come up with a solution that overcomes the long-standing problem. Researchers have developed a new technique that combines scanning tunneling microscopy and ultra-fast laser pulses in such a way that both can play to their strengths, without their weaknesses playing spoilsport.

Many technical applications, such as the development of solar cells or new types of electronic components need a mapping of the dynamics of electrons in molecules and solids as exactly as possible.

“The new microscopy technique uses laser pulses to modulate the tunnel current through targeted excitation of the electrons in the material. The necessary ultrafast laser pulses in the attosecond range cannot be bought off the shelf. But thanks to the rapid development of laser technology in recent years, we have succeeded in generating exactly the right pulses”, explained Dr. Garg.

The new technology involves firing two pulses at the molecule to be examined with a slight time delay from each other and scanning it in the process. By repeating this procedure several times with varied time gaps between the pulses, they got a series of images that reproduced the behavior of the electrons in this molecule with atomic precision. The fast laser pulses provide information about the electron dynamics, while the scanning tunneling microscope precisely scans the molecule.

Speaking to India Science Wire, Dr. Garg said, “the new technique enabled us for the first time to directly map the dynamics of the electrons in molecules as they jump from one orbital to another. It provides completely new possibilities for directly observing quantum mechanical processes such as charge transfer in individual molecules and thus for better understanding them”.

The new technique is expected to help provide decisive new insights, especially in charge transfer processes, which play a decisive role in many biophysical reactions as well as in solar cells and transistors. The researchers have published a report on their findings in the science journal, Nature Photonics.