After more than ten years of rapid development, the efficiency of perovskite solar cells (PSCs) has already exceeded 26% in the laboratory. Many companies have begun to set up production lines for PSCs in the hope of mass-producing modules, and mature products are just around the corner. However, due to the gap between the harsh device fabrication conditions in the laboratory and the industrial production environment, module samples are still limited by the long-term stability of the device. Therefore, in addition to improving the device fabrication process, a thorough understanding of the crystallization mechanism of perovskite materials is an important part of improving device stability from a manufacturing perspective. 
Generally speaking, the controllable crystallization rate of perovskite enables the production of high-quality films, resulting in high performance solar cells. Our work shows that FAPbI3 has the longest crystallization formation time of all the pure phases of perovskite and can therefore be used to obtain films with low defect density. However, it tends to form the hexagonal non-perovskite polymorph, making it challenging for photovoltaic applications. After a thorough discussion of the perovskite crystallization process, MACl is selected as the crystallizing agent to modulate the intermediate phase and obtain a controllable crystallization rate to produce black phase perovskite films. In addition, MABr is used to heal defects and passivate FAPbI3 to obtain air-stable films. The perovskite solar cell produced using this strategy has an efficiency of 23.0%. [1]
Based on the concern that MABr may affect the growth of pure phase perovskites, we introduce (the green) dimethyl sulfide (DMS) as a novel nucleation trigger for perovskite films, uniquely combining high coordination and low vapor pressure. More specifically, DMS is more coordinative than all currently used solvents and thus effectively replaces them, including DMSO, during film formation. Crucially, DMS also has one of the highest vapor pressures reported in the literature, so it effectively leaves the thin film shortly after formation. This gives DMS universal applicability: DMS replaces other solvents by coordinating more strongly, and removes itself once film formation is complete. To demonstrate this novel coordination chemistry approach, we process MAPbI3 PSCs, typically dissolved in hard-to-remove (and green) DMSO, achieving 21.6% efficiency, one of the highest reported efficiencies for this system. This work provides a universal strategy to control perovskite crystallization using coordination chemistry and heralds the revival of perovskite compositions with pure DMSO, such as MAPbI3. [2]