Simple salt could help unlock more powerful perovskite solar cells

A salt called guanidinium thiocyanate can improve the efficiency and stability of perovskite solar cells, a new class of semiconductor that could make solar power cheaper and more powerful, according to researchers at UCL.

In a study published in the Journal of the American Chemical Society, the team showed that guanidinium thiocyanate can slow and control the way perovskite crystals form during fabrication, creating smoother and more uniform layers. This helps reduce the tiny flaws in the material that can hinder performance and shorten a cell’s lifespan.

Tandem perovskite cells—that is, two or more layers of solar cells stacked on top of each other—are seen as the future of ultra-efficient solar energy technology. That is because each layer can be tuned to absorb different parts of the solar spectrum, meaning they can convert more of that light into electricity. The new study used mixed tin-lead perovskites—typically the bottom layer of stacked cells.

Corresponding author Dr. Tom Macdonald (UCL Electronic & Electrical Engineering) said, “Our approach provides a straightforward, effective way to enhance perovskite quality during manufacturing, delivering solar cells that are both higher performing and more stable, key requirements for commercial success.”

In tests, the team achieved an efficiency of 22.3% for this material, close to the best reported for mixed tin-lead perovskites. For comparison, the best silicon solar cells in the lab have reached around 27% efficiency, while most commercial panels installed on rooftops today deliver about 22%. All-perovskite tandem devices (that is, using more than one layer of perovskite cell) have already surpassed 30% in the lab, highlighting their potential to achieve a step-change in solar power generation.

Using salt as demonstrated by the UCL team for the bottom layer of tandem cells—either guanidinium thiocyanate or potentially another agent—would likely increase this world-record efficiency further.

Perovskite solar cells are already known for their tolerance to defects, but reducing those defects as far as possible is key to unlocking higher efficiencies and longer-lasting devices. The guanidinium additive works by giving researchers greater control over crystal growth, limiting the imperfections that occur when the material forms too quickly.

First author Yueyao Dong (UCL Electronic & Electrical Engineering) said, “This work gave us valuable insight into the crystal formation process. By modulating it in a controlled way, we were able to create much higher-quality films—a change that directly translates into more efficient and longer-lasting devices.”

Co-author Dr. Chieh-Ting Lin (National Chung Hsing University) added, “It opens the door to fine-tuning the structure of perovskites for high-performance tandem solar cells, with the potential to significantly push the limits of efficiency.”

Perovskite solar cells have emerged over the past decade as a leading alternative to traditional silicon-based solar panels. Like silicon, perovskites are semiconductors—materials that can conduct electricity under certain conditions.

An advantage of perovskites is that they can be made at low temperatures using simpler, less energy-intensive processes. This makes them attractive for large-scale manufacturing and opens possibilities for lightweight, flexible solar panels.

Perovskite cells can also be tuned to capture different parts of the solar spectrum, making them ideal for tandem solar cells. Tandem cells can either combine perovskite with silicon to harvest more sunlight, or be configured as all-perovskite tandems, which offer enhanced light-harvesting tunability and greater manufacturing flexibility.

While guanidinium salts have been used in perovskite research before, this study provides new insight into how they influence crystal formation and how this can lead to more efficient and stable solar cells. The work builds on earlier research by the team, published in ACS Energy Letters, which showed that guanidinium can also help improve charge transport and reduce the unwanted movement of ions within the cell.

As the demand for clean energy grows, the ability to manufacture high-efficiency, low-cost solar cells at scale will be crucial. Advances like these could help overcome the remaining roadblocks to commercializing perovskite technology, opening the way for next-generation solar panels that are more efficient, more durable and more affordable.