In Situ Metrology of Hybrid Halide Perovskite Single Crystals—Investigating Growth Dynamics of Inverse Temperature Crystallisation

Following the discovery of inverse temperature crystallisation phenomena of single crystal hybrid halide perovskites in specific solvent pairings,^1,2 the rapid growth of high quality single crystal perovskites by this technique has been widely adopted. This has proven immensely useful in differentiating fundamental material properties from those derived from the granular structure of thin-film counterparts.³ As methods to structurally characterise halide perovskite systems become increasingly intensive, it remains imperative to provide due care to simultaneously advancing our understanding of materials synthesis.<br/>Here, we present an <i>in-situ</i> study and analysis of methylammonium lead bromide (MAPbBr₃) single crystal growth. The space-confined inverse temperature growth of MAPbBr₃crystals is monitored in real-time using optical microscopy methods examining many relevant experimental conditions including temperature and solute concentration. MAPbBr₃ is selected as an ideal model system, with stable cubic phase within the relevant temperature window of growth and convenient solubility profile. Individual surface facets are monitored and growth rates extracted. We understand this to be the first time that the tracking of individual hybrid perovskite crystal facets has been demonstrated using advanced image analysis techniques.<br/>Our method reveals inhomogeneity in the growth rates of crystallographically identical facets and the importance of mass transfer and concentration gradients. Regions of accelerated growth rate lead to excess defect incorporation and diminished crystalline quality within one “single crystal”. We identify the often overlooked complexities of relevant thermodynamic and kinetic crystal growth within the phenomena of inverse temperature crystallisation, the fundamental understanding of which has remained limited since first reported in 2015.<br/><br/>1. Saidaminov, M. I. <i>et al.</i> High-quality bulk hybrid perovskite single crystals within minutes by inverse temperature crystallization. <i>Nat. Commun.</i> <b>6</b>, 7586 (2015).<br/>2. Saidaminov, M. I., Abdelhady, A. L., Maculan, G. & Bakr, O. M. Retrograde solubility of formamidinium and methylammonium lead halide perovskites enabling rapid single crystal growth. <i>Chem. Commun.</i> <b>51</b>, 17658–17661 (2015).<br/>3. Stavrakas, C. <i>et al.</i> Probing buried recombination pathways in perovskite structures using 3D photoluminescence tomography. <i>Energy Environ. Sci.</i> <b>11</b>, 2846–2852 (2018).