Single-crystal perovskites have emerged as a promising class of materials for optoelectronic applications due to their superior electronic and optical properties compared to polycrystalline films. The growth of high-quality single crystals is critical for achieving low defect densities, long carrier diffusion lengths, and high optoelectronic homogeneity. Several techniques have been developed to grow single-crystal perovskites, each with distinct advantages and challenges. This article focuses on two prominent methods: inverse temperature crystallization (ITC) and antisolvent vapor diffusion (AVD), comparing their outcomes in terms of material quality and performance.

Inverse temperature crystallization is a widely used technique for growing large, high-quality single crystals of perovskites. The method exploits the retrograde solubility behavior of perovskite precursors in certain solvents, where solubility decreases with increasing temperature. A precursor solution is prepared at room temperature and then heated gradually, causing supersaturation and subsequent crystal nucleation and growth. ITC has been successfully applied to grow methylammonium lead trihalide (MAPbX3, where X = I, Br, Cl) and formamidinium lead trihalide (FAPbX3) single crystals with dimensions exceeding several millimeters. The slow heating process allows for controlled nucleation, reducing defect formation and enhancing crystal quality. Defect densities in ITC-grown single crystals are typically in the range of 10^9 to 10^10 cm^-3, significantly lower than those in polycrystalline films. The reduced defect density contributes to carrier diffusion lengths exceeding 10 micrometers, making these crystals suitable for high-performance optoelectronic devices. Additionally, ITC-grown crystals exhibit excellent optoelectronic homogeneity, with minimal spatial variations in photoluminescence and charge carrier mobility.

Antisolvent vapor diffusion is another effective method for growing single-crystal perovskites, particularly for systems where ITC may not be applicable. In AVD, a perovskite precursor solution is exposed to an antisolvent vapor, which gradually diffuses into the solution, reducing the solubility of the perovskite and inducing crystallization. This method is particularly useful for growing mixed-halide and mixed-cation perovskites, where precise control over composition is required. AVD-grown single crystals often exhibit defect densities comparable to those achieved via ITC, ranging from 10^9 to 10^11 cm^-3, depending on the specific perovskite composition and growth conditions. Carrier diffusion lengths in AVD-grown crystals are also impressive, often exceeding 5 micrometers, though slightly shorter than those in ITC-grown crystals due to subtle differences in defect distribution. Optoelectronic homogeneity in AVD-grown crystals is generally high, but slight compositional gradients can occur if the antisolvent diffusion is not uniformly controlled.

Comparing the two techniques, ITC tends to produce larger single crystals with slightly lower defect densities and longer carrier diffusion lengths, making it ideal for fundamental studies and applications requiring high material quality. However, ITC is limited to perovskites with retrograde solubility and may not be suitable for all compositions. AVD, on the other hand, offers greater flexibility in terms of perovskite composition and can be adapted to grow crystals of materials that are not amenable to ITC. The trade-off is a slightly higher defect density and shorter carrier diffusion length, though these differences are often marginal and may not significantly impact device performance.

Both techniques face challenges in scaling up for industrial applications. ITC requires precise temperature control and long growth times, which can be impractical for large-scale production. AVD, while more versatile, demands careful optimization of antisolvent concentration and diffusion rates to avoid uncontrolled nucleation and polycrystalline growth. Additionally, both methods struggle with the incorporation of certain dopants or mixed compositions without introducing defects or phase segregation. For example, growing mixed halide perovskites with uniform halide distribution remains a challenge due to the tendency of halides to segregate during crystallization.

Despite these challenges, advancements in single-crystal perovskite growth have enabled significant improvements in device performance. Single-crystal perovskites exhibit superior charge transport properties compared to their polycrystalline counterparts, leading to higher efficiency in solar cells, brighter and more stable light-emitting diodes, and more sensitive photodetectors. The reduced defect density in single crystals also enhances device stability, as defects often act as degradation initiation sites under operational stresses.

Future research directions include the development of hybrid growth techniques that combine the advantages of ITC and AVD while mitigating their limitations. For instance, combining temperature control with antisolvent engineering could yield crystals with even lower defect densities and improved compositional uniformity. Additionally, exploring new solvent systems and growth additives may further enhance crystal quality and enable the growth of previously inaccessible perovskite compositions.

In summary, inverse temperature crystallization and antisolvent vapor diffusion are two leading techniques for growing single-crystal perovskites, each offering unique benefits and facing distinct challenges. ITC excels in producing large, high-quality crystals with minimal defects, while AVD provides greater compositional flexibility. Both methods contribute to the advancement of perovskite optoelectronics by enabling materials with superior electronic and optical properties. Continued innovation in growth techniques will be essential for unlocking the full potential of single-crystal perovskites in next-generation devices.