Light flashes boost bismuth oxide photocurrent up to 50-fold

A pale-gray film turns bright yellow under a flash lasting less than a millisecond. In the Jerusalem lab of Shahar Artzi and Ronen Gottesman, that color change marked a new atomic arrangement in bismuth oxide—and a photocurrent up to 50 times higher than in the material’s ordinary form.

The trick is to heat only the thin semiconductor coating. The team’s white-light pulses drove the film to nearly 2,000°C, while the transparent conducting glass beneath it stayed below 100°C. Conventional furnaces heat both layers together, and the glass and its conducting coating do not tolerate much above 500–600°C.

Bismuth oxide can take two crystal forms, or polymorphs—different atomic arrangements with the same chemical composition. Longer flashes produced the stable alpha phase; shorter, more powerful flashes trapped the less stable beta phase at room temperature. The beta structure absorbs a wider range of visible light and produced between 10 and 50 times more photocurrent, depending on how the film was prepared.

The pulse’s timing mattered more than the total energy delivered: two pulses with identical energy produced different materials when that energy arrived at different speeds. The researchers could also switch the film repeatedly between the alpha and beta phases, directly on transparent conducting glass.

So what changes in practice? A process that could eventually improve solar technologies could avoid exposing the entire device stack to extreme heat. The immediate result is a way to test high-temperature crystal structures on surfaces used in solar cells and touchscreens, while keeping the supporting glass cool. The study remains a laboratory result, and the researchers describe broader applications as potential rather than deployed technology.