University of Washington researchers show in a new study that perovskite material contains flaws that can be engineered to improve solar cells and other devices even further.

UW researchers used confocal optical microscopy to identify inefficient regions in perovskite materials. The flaws are evidenced by dark areas in image C. Image Credit: University of Washington  Click image for the largest view.

UW researchers used confocal optical microscopy to identify inefficient regions in perovskite materials. The flaws are evidenced by dark areas in image C.
Image Credit: University of Washington.  Click image for the largest view.

A new study published online in the journal Science by the University of Washington (UW) and University of Oxford researchers demonstrates that perovskite materials, generally believed to be uniform in composition, actually contain flaws that can be engineered to improve solar devices even further.

Perovskites are promising light harvesters that could revolutionize the solar and electronics industries because they show potential to convert sunlight into electricity more efficiently and less expensively than today’s silicon-based semiconductors.

These super efficient crystal structures have taken the scientific community by storm in the past few years because they can be processed very inexpensively and can be used in applications ranging from solar cells to light-emitting diodes (LEDs) found in phones and computer monitors.

Lead author Dane deQuilettes, a UW doctoral student working with David Ginger, professor of chemistry and associate director of the UW’s Clean Energy Institute said, “Perovskites are the fastest-growing class of photovoltaic material over the past four years. In that short amount of time, the ability of these materials to convert sunlight directly into electricity is approaching that of today’s silicon-based solar cells, rivaling technology that took 50 years to develop. But we also suspect there is room for improvement.”

The research team used high-powered imaging techniques to find defects in the perovskite films that limit the movement of charges and, therefore, limit the efficiency of the devices. Perovskite solar cells have so far have achieved efficiencies of roughly 20 percent, compared to about 25 percent for silicon-based solar cells.

In a collaboration made possible by the Clean Energy Institute, the team used a technique called confocal optical microscopy, which is more often used in biology, and applied it to semiconductor technology. They used fluorescent images and correlated them with electron microscopy images to find “dark” or poorly performing regions of the perovskite material at intersections of the crystals. In addition, they discovered that they could “turn on” some of the dark areas by using a simple chemical treatment.

According to corresponding author David Ginger, the Alvin L. and Verla R. Kwiram Endowed Professor of Chemistry and Washington Research Foundation Distinguished Scholar, the images offered several surprises but also will lead to accelerated improvements in the materials’ uniformity, stability and efficiency.

Ginger said, “Surprisingly, this result shows that even what are being called good, or highly-efficient perovskite films today still are ‘bad’ compared to what they could be. This provides a clear target for future researchers seeking to improve and grow the materials.”

Professor Ginger also noted the imaging technique developed by the UW team also offers an easy way to identify previously undiscovered flaws in perovskite materials and to pinpoint areas where their composition can be chemically altered to boost performance.

deQuilettes, who spearheaded the project as a Clean Energy Institute graduate fellow, estimates there are more than a thousand laboratories around the world currently researching the semiconducting properties of perovskite materials. Yet there is more work to be done to understand how to consistently make a material that is stable, has uniform brightness and can stand up to moisture without degrading. The UW research offers new ways for people to think strategically about how to improve the materials and how to extend their applications to high performance light-emitting devices such as LEDs and lasers.

deQuilettes said, “There are so many of us focusing on perovskites, so hopefully this technique will offer some new direction and steer us toward the places we can look to optimize their energy-capturing and emitting potential.”

Hopefully this news will circulate quickly. Perovskites seem to be at the cutting edge of the next stage in light technology both in the harvesting and in use. There probably aren’t enough confocal optical microscopy slots available for now, but that will change soon.

Coming up is a series of flaw identification, chemical doping and a long set of steps in the run to 30% efficiency. Your humble writer is confident that the field will get there and perhaps well beyond.


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