Researchers in Australia have solved a fundamental challenge preventing the widespread adoption of next-generation perovskite solar cells.
Metal halide perovskites, a class of hybrid organic-inorganic materials, offer an inexpensive, flexible, and promising avenue for efficient solar photovoltaics, as well as light-emitting devices and fast X-ray detectors.
Since perovskite materials have gained prominence over the past decade, scientists and engineers have faced several problems that preclude their widespread use in commercial applications.
This includes light-induced phase separation, in which lighting such as sunlight disrupts the carefully arranged composition of elements in perovskites with mixed halide.
This in turn leads to an instability of the band gap of the material, which perturbs the wavelengths of the absorbed light, while the charge carrier conduction and the efficiency of the components are reduced.
Now, however, an unlikely solution has been found.
Members of the ARC Center of Excellence for Exciton Research have shown that high intensity light cancels the disturbance caused by light at lower intensities and that this approach can be used to actively control the band gap of the material.
The results were published in the journal Nature Materials.
Dr. Chris Hall, member of Professor Trevor Smith’s team at the University of Melbourne, and Dr. Wenxin Mao from Professor Udo Bach’s group at Monash University recognized for the first time the potential of exploring this research path in a separate experiment.
“It was one of those unusual discoveries you sometimes hear about in science,” said Chris.
“We took a measurement, looked for something else, and then came across this process, which seemed quite strange at the time. We quickly realized, however, that it was an important observation.”
They asked Dr. Stefano Bernardi, a member of Dr. Asaph Widmer-Cooper at the University of Sydney for help who led the computer modeling work to better understand their surprising solution to the problem.
Stefano said: “We found that with increasing excitation intensity, the local strains in the ion lattice that were originally the cause of the segregation merge. In this case, the local deformations that led to the segregation disappear.
“On a normal sunny day, the intensity is so low that these deformations are still localized. However, if you find a way to increase the excitation above a certain threshold, for example using a solar concentrator, the segregation disappears.”
The implications of the results are significant as researchers are now able to maintain the optimal composition of the elements in mixed halide perovskites when exposed to light necessary for use in solar cells.
“A lot of people have approached this problem by looking for ways to suppress light-induced interference, such as looking at different compositions of the material or changing the dimensions of the material,” said Chris.
“We have shown that you can actually use the material in the state you would like to use it in a solar cell. All you have to do is focus more light on it.
“An exciting addition to this work is that the ability to quickly switch the band gap with light opens up an interesting opportunity to use perovskites for data storage,” said Wenxin.
Chris added, “We did the basic work and the next step is to put it on a device.”