Researchers from University College London (UCL), National Chung Hsing University, Queen Mary University of London, University of Washington and London South Bank University have found that guanidinium thiocyanate (GASCN), a chaotropic agent, can slow and control the way perovskite crystals form during fabrication, creating smoother and more uniform layers. This helps reduce defects in the material that can hinder performance and shorten a solar cell’s lifespan.
The team focused on mixed tin-lead perovskites – typically the bottom layer of stacked cells in a tandem architecture. The scientists reported on the use of GASCN as a chaotropic agent to improve the film quality and device performance of mixed Sn–Pb perovskites. The use of the guanidinium additive gives researchers greater control over crystal growth, limiting the imperfections that occur when the material forms too quickly.
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.
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."
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, which showed that guanidinium can also help improve charge transport and reduce the unwanted movement of ions within the cell.
