Simple Salt Additive Controls Crystal Growth for Better Solar Cells

Wide-bandgap perovskites are a vital component for creating ultra-efficient tandem solar cells, but their potential has been hampered by a chaotic crystallisation process. When these materials are made, a strong attraction between the chemical precursors and the solvent causes crystals to form and grow in an unbalanced way, leading to defects, instability, and poor performance.

Now, researchers have found a simple yet powerful solution: adding ammonium chloride (AC) into the mix. This common salt acts as a chemical director, weakening the problematic precursor-solvent bond. This allows for a more controlled, balanced formation of crystals.

The AC provides ideal starting points for the desired cubic crystal structure to grow while simultaneously suppressing unwanted hexagonal shapes. It also retards runaway crystal growth through a process of ion exchange. The result is a more uniform, higher-quality perovskite film with fewer defects, leading to solar cells that achieve around 18% efficiency with enhanced photostability, paving the way for better photovoltaic technologies.