Volatile Molecules Tune Crystallisation for Record-Breaking Solar Efficiency

Perovskite solar cells (PSCs) offer immense potential for renewable energy, yet their development is often hindered by energy losses resulting from imperfect crystal structures and microscopic defects. To overcome this, scientists investigated the use of volatile positional isomers—molecules with identical atomic formulas but different structural arrangements—of methoxythioanisole (MTA) to regulate the film formation process.

The study revealed that the meta- isomer, known as m-MTA, provided the optimal balance of chemical properties. By interacting with lead and formamidinium components within the mixture, m-MTA effectively slows down the reaction. This extended crystallisation time allows for homogeneous nucleation, ensuring the crystal lattice forms in a highly ordered, defect-free manner. Crucially, because the molecule is volatile, it evaporates completely, leaving no residue to interfere with the final film's performance.

The results of this additive engineering are striking. Devices treated with m-MTA achieved a champion power conversion efficiency (PCE) of 26.46% with minimal voltage loss, and scaled 1 cm² devices maintained a robust 24.75% PCE. Furthermore, the unencapsulated cells displayed exceptional durability, retaining over 90% of their initial efficiency after 1,440 hours of continuous operation under simulated sunlight. This work establishes that exploiting subtle differences in molecular geometry is a powerful strategy for mitigating defects and boosting the viability of perovskite technology.