Abstract
Solution-processable halide perovskites have emerged as strong contenders for next-generation solar cells owing to their favorable optoelectronic properties. To maintain the efficiency momentum of perovskite solar cells (PSCs), development of advanced processing techniques, particularly for the perovskite layer, is imperative. There is a close correlation between the quality of the perovskite layer and its photophysical properties: Highly crystalline large grains with uniform morphology of the perovskite layer and their interface with charge transporters are crucial for achieving high performance. Significant efforts have been dedicated to achieve perovskite films with large grains reaching the millimeter-scale for high-efficiency PSCs. Recent work showcases a transition from large grain polycrystalline to single-crystalline (SC) PSCs made possible by the facile growth of perovskite single crystals. In this review, the recent progress of the large grain polycrystalline PSCs and grain boundary-free SC-PSCs is reported, particularly focusing on the recent approach of depositing large-grained perovskite layers and single crystal growth technique, that have been adopted for fabrication of efficient PSCs. In addition, prospects of SC-PSCs and their further development in terms of efficiency, device design, scalability, and stability are discussed.