A powerful flash of light lasting less than a millisecond could offer a new way to make materials that capture solar energy much more effectively—without damaging the surface underneath.
Researchers at the Hebrew University of Jerusalem have developed a technique that uses extremely short bursts of intense light to rearrange atoms inside a semiconductor material.
The resulting material generated up to 50 times more electrical current from light than its ordinary form.
The study, published in Small Structures, was led by Shahar Artzi and Dr. Ronen Gottesman from the university’s Institute of Chemistry and Center for Nanoscience and Nanotechnology.
Many materials can have the same chemical ingredients but very different internal structures. A familiar example is carbon: both diamond and graphite are made entirely of carbon, but their atoms are arranged differently, giving them dramatically different properties.
Semiconductors can behave in a similar way. Some atomic arrangements may be much better at absorbing light or conducting electricity. Unfortunately, these useful structures can be difficult to produce and keep because they may exist only at very high temperatures.
Traditional furnaces aren’t an ideal solution. They heat both the material being treated and the surface underneath it. This is a serious problem for transparent conducting glass, which is widely used in solar cells and touchscreens because it cannot withstand extremely high temperatures.
The researchers found a way around this problem using what is known as flash photonic heating.
They placed a thin coating of bismuth oxide on conducting glass and exposed it to extremely powerful flashes of white light. Each flash lasted from about one-tenth of a millisecond to a few milliseconds.
The coating absorbed the energy so quickly that its temperature approached 2,000°C, while the glass underneath remained below 100°C. Heating rates reached as high as 10 million degrees Celsius per second.
Just as importantly, the material cooled extremely quickly. This prevented its atoms from returning to their usual arrangement.
The researchers compare the process to a blacksmith rapidly cooling hot steel. Fast cooling can lock the metal into a structure that would disappear if it cooled slowly. In this case, however, the researchers accomplish the transformation with light.
By changing the strength and duration of the flashes, the team could control which form of bismuth oxide appeared. Longer flashes produced its normal stable form, which was pale gray. Shorter, more intense flashes created a less stable form that remained at room temperature and appeared bright yellow.
The yellow form was particularly interesting because it absorbed more visible light. Depending on how it was prepared, it generated between 10 and 50 times more electrical current from light than the ordinary form.
The scientists achieved this improvement without changing the material’s chemical composition. They simply changed how its atoms were arranged.
They were also able to repeatedly switch the material between the two forms directly on conducting glass.
Although the experiments focused on bismuth oxide, the researchers believe the technique could work with other materials used in solar energy, electronics and technologies that use light to drive chemical reactions.
The team is now investigating whether the method could even work on plastics and flexible surfaces, potentially opening the door to new lightweight and flexible solar and electronic devices.
