Power/Performance Bits: Nov. 25

The use of a perovskite solution in a semiconductor device could improve the quality and manufacturing efficiency of imaging devices, according to UCLA researchers; a University of Oregon microscope puts the spotlight on the surface structure of quantum dots for designing new solar devices.

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Better photodetectors
Photodetectors are semiconductor devices that convert incoming light into electrical signals used in a vast array of products, from visible and infrared light detection systems to television remote controls. Meanwhile, perovskite is an organic-inorganic hybrid material with a crystal structure that is very efficient at converting light into electricity, and in recent years, the use of perovskite materials has led to rapid advances in the efficiency of solar cells.

Now, a UCLA research team has developed a photodetector that uses thin coatings of perovskite — rather than silicon or other common materials—that can efficiently and quickly transports signals with minimum loss. It also offers improved sensitivity under dim light.

The perovskite coating is roughly 300nm, while the silicon layer in common photodetectors is 100 micrometers, or more than 330 times as thick.

The new perovskite photodetector developed at the UCLA Henry Samueli School of Engineering and Applied Science. (Source: UCLA)

The new perovskite photodetector developed at the UCLA Henry Samueli School of Engineering and Applied Science. (Source: UCLA)

The researchers believe the device has the potential to improve the efficiency and contrast in optical sensors used in various applications. Their production requires less energy and time than is currently needed to make photodetectors, and so promises to make manufacturing on the industrial scale very cost-efficient.

Improved nanomaterials
A collaboration of University of Oregon and industry researchers has resulted in a potential path to identify imperfections and improve the quality of nanomaterials for use in next-generation solar cells.

To increase light-harvesting efficiency of solar cells beyond silicon’s limit of about 29 percent, manufacturers have used layers of chemically synthesized semiconductor nanocrystals. By controlling the synthetic process and surface chemical structure, properties of quantum dots can be manipulated.

However, the process creates imperfections at the surface-forming trap states that limit device performance and until recently, improvements in production quality have relied on feedback provided by traditional characterization techniques that probe average properties of large numbers of quantum dots.

Researchers investigated electronic states of lead sulfide nanocrystals. By using a specially designed scanning tunneling microscope, researchers created atomic-scale maps of the density of states in individual nanocrystals. This allowed them to pinpoint the energies and localization of charge traps associated with defects in the nanocrystal surface structure that are detrimental to electron propagation.

This work is expected to help manufacturers tweak their synthesis of nanocrystals used in a variety of electronic devices, the researchers said. Specifically, they believe the information will help to fine-tune the ligand chemistry to make better devices for photovoltaics, detectors and sensors.