Advancing Perovskite Single Crystal Fabrication: Enhanced Crystallinity and Reproducibility through Feedback Control of Linear Growth Rate

Lead halide perovskites have gained significant attention in recent years thanks to their excellent photon absorption capabilities and charge transport properties, raising high expectations for diverse device applications such as solar cells and X-ray detectors. However, their instability presents a major challenge that demands resolution. Notably, perovskite single crystals are known to exhibit substantially higher durability compared to polycrystalline films, with an even higher degree of crystallinity suggesting enhanced stability. Nevertheless, conventional methods for synthesizing perovskite single crystals have often been relatively straightforward, yet challenging to consistently produce high-quality single crystals.<br/>In light of this, our research focused on controlling the linear growth rate of the single crystals which has been likely overlooked in the conventional methods. Methylammonium lead tribromide (MAPbBr₃) single crystals are fabricated as a case study. Our novel approach combines in-situ imaging techniques to monitor crystal growth rates with a conventional solvent evaporation method. When the crystal growth deviates from the desired rate, our system provides feedback to adjust growth conditions accordingly. Through this approach, we successfully maintain a constant linear growth rate for over 60 hours, leading to the reproducible synthesis of single crystals with enhanced crystallinity.<br/>The degree of crystallinity is quantified by measuring the rocking curves of the (100) plane of the obtained MAPbBr₃ single crystals. This work uncovers the critical role of controlling the linear growth rate, rather than the mass growth rate, in achieving superior crystallinity and reproducibility. MAPbBr₃ single crystals grown with a linear growth rate of less than 0.3 mm h^-1 exhibit narrow rocking curves, with a full width at half maximum (FWHM) of 19.0±2.7 arcsecs (n=17), while growth rates exceeding 0.3 mm h^-1 results in a FWHM of 27.9±10.0 arcsecs (n=15). The best crystal achieves a remarkable FWHM of 15.3 arcsecs, the narrowest reported for MAPbBr₃ single crystals, comparable to a commercial silicon wafer. Note that these excellent FWHM are achieved with centimeter-scale single crystals. This research emphasizes the pivotal importance of linear growth rate control in single crystal growth.