Environment Technology

Perovskite Solar Cells Exceed 20 Percent Efficiency

solar cells perovskite

Ecole Polytechnique Fédérale de Lausanne researchers are currently working on pushing the limits of perovskite solar cell performance by exploring new ways to grow these unique crystals.

Michael Graetzel and his team discovered that by reducing the pressure for brief periods of time while fabricating perovskite crystals, they are able to reach much better performances. These performances are so massive, in fact, that they are the best ever measured for larger-sized perovskite solar cells, reaching numbers of more than 20 percent efficiency and matching the performance of conventional thin-film solar cells of similar sizes.

The news is very promising in the perovskite technology world, where costs are already exceptionally low and industrial developments are always taking place to further the use and function of the technology. The downside, however, is that higher performances within pervoskites are not necessarily able to prevent the terrible fate of the silicon-based solar technology. There are a number of safety issues that still need to be addressed, such as the amount of lead content found within current perovskite solar-cell prototypes as well as their stability. The stabilities of the actual devices are still being determined and may take a decent amount of time to calculate accurately.

perovskite solar cell
Prototype showing perovskite solar cell. (Image credit:
Alain Herzog / EPFL)

Stacking pervoskites on top of silicon in order to create hybrid solar panels may be the best way to boost the silicon solar-cell industry. Efficiency may actually be able to skyrocket far beyond 30 percent, with a theoretical limit of about 44 percent, something that may be increased with follow-up research. The improvement in terms of performance means more solar energy being harnessed. This will lead to much higher energy light being absorbed by the perovskite top layer, while lower energy sunlight will pass through the perovskite and being absorbed by the silicon layer.

Graetzel is best known for his transparent dye-sensitized solar cells. Researchers have discovered that the very first perovskite solar cells were dye-sensitized cells where small perovskite particles took the place of the dye. The lab’s most recent prototype is about the size of an SD card and looks like a piece of glass that is darker on one side by a thin film of perovskite. The perovskite solar cell is opaque.

Scientists have to grow crystals that have a special structure known as the perovskite in order to create the perovskite solar cell. They must first dissolve a selection of components in a liquid that they turn into “ink”. The ink is then placed on a special type of glass that is able to conduct electricity. The ink dries, leaving behind a thin film that crystallizes on top of the glass when mild heat is applied. The final result is a thin layer of perovskite crystals.

The tricky part is growing thin crystal films that result in solar cells that can absorb the maximum amount of light possible. Scientists are always searching for smooth and regular layers of the material with large crystal grain size in order to increase the yields of photovoltaic.

Spinning the cell when the ink is not yet dry allows it to be flattened even further and wicks off some of the extra liquid, leading to much larger films. Graetzel and his team have come up with a new vacuum flash technique that is able to selectively remove the volatile components of this additional liquid. During the same process, the burst of vacuum flash creates seeds for crystal formation. This leads to very regular and shiny perovskite crystals that have high electronic quality.

The complete results can be found in Science journal, which was published earlier this month.