Perovskite solar cells (PSCs) have become one of the most promising candidates for next-generation photovoltaics. In the precise control of the crystallographic orientation of perovskite films, randomly oriented grains often lead to uneven charge transport and accelerated degradation, limiting the performance and stability of PSCs. 

It is crucial to achieve a uniform and well-defined crystal orientation to develop high-efficiency and durable devices. In a study published in Energy & Environmental Science, a research team led by Prof. LI Can from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences developed a solvent-additive cascade regulation (SACR) strategy which enables the controlled growth of single-oriented perovskite films.

The team has been systematically exploring how crystal facet orientation affects the optoelectronic properties of perovskite materials. Its previous studies have developed methods to induce highly (111)-oriented perovskite films, achieved ordered stacking of (001)-oriented crystals, and revealed the crucial role of facet distribution in determining device performance.

In this study, researchers demonstrated that solvent composition and additive chemistry cooperatively determine the crystallographic orientation of perovskite films during solution growth. They found that the solvent composition governs the formation of specific intermediate phases that serve as structural templates for nucleation. 

For example, the N,N-dimethylformamide (DMF) /dimethyl sulfoxide (DMSO) system forms PbI₂·DMSO adducts favoring (111)-facet nucleation, whereas the DMF/N-methyl-2-pyrrolidone (NMP) system produces PbI₂·(DMF/NMP) complexes that promote (100)-facet growth. Meanwhile, cyclohexylamine and cyclohexylammonium iodide act as facet-selective additives, modulating facet-dependent crystallization kinetics through selective adsorption or chemical reactions.

Moreover, researchers established a direct link between solvent coordination, facet-dependent growth dynamics, and film orientation. They achieved precise orientation control and produced single-oriented perovskite films through SACR strategy. (100)-oriented devices achieved a power conversion efficiency of 25.33% with enhanced charge transport, and (111)-oriented devices exhibited superior environmental stability—retaining over 95% of their performance after 2,000 hours of ambient exposure.

"Our solvent-additive cascade strategy bridges solvent chemistry and crystal growth dynamics, enabling controllable orientation in perovskite films. This study deepens our understanding of facet-driven performance and offers new opportunities to design more efficient and stable perovskite solar technologies," said Assoc. Prof. LIU Jiewei from DICP, co-corresponding author of the study.