Recent progress of crystal orientation engineering in halide perovskite photovoltaics

Manipulating the crystallographic orientation of semiconductor crystals plays a vital role in fine-tuning their facet-dependent properties, such as surface properties, charge transfer properties, trap state density, and lattice strain. The success in crystal orientation engineering enables the preferential growth orientation of perovskite thin films with favorable crystal planes by precise nucleation manipulation and growth condition optimization, rendering the films with the unique optoelectronic properties to further improve the efficiency of perovskite solar cells (PSCs). However, the origin and impact of preferential crystallographic orientation of perovskite thin films on the corresponding photovoltaic performance of PSCs are still far from being well understood. Herein, we explore the crystal orientation-dependent optoelectronic properties of halide perovskites and their influence on the photovoltaic performance of PSCs. We summarize the basic strategies for crystal facet engineering in the fabrication of preferentially oriented perovskite thin films, with a focus on the oriented growth mechanism during thin film formation. Based on the above knowledge and the recent research progress in terms of crystal orientation engineering in PSCs, a brief outlook on the remaining challenges and perspectives are provided.