Facet Engineering: A Promising Pathway toward Highly Efficient and Stable Perovskite Photovoltaics.

Perovskite solar cells are considered to be important candidates for future energy applications. The facet orientation causes anisotropy in the photoelectric and chemical properties of the surface of perovskite films and therefore might affect the photovoltaic properties and stability of the devices. Facet engineering has attracted increasing attention only recently in the perovskite solar cell community, and related deep investigation is rather rare. To date, it is still difficult to precisely regulate and directly observe perovskite films with specific crystal facets due to the limitations of solution methods and characterization technology. Consequently, the link between facet orientation and photovoltaic performance of perovskite solar cells is still controversial. Herein, we highlight the latest progress in the means of direct characterization and regulation of crystal facets and briefly analyze the existing issues and future perspectives of facet engineering in perovskite photovoltaics.