Self-assembly and templated growth techniques have emerged as powerful strategies for controlling the morphology, crystallinity, and functionality of perovskite semiconductors. These methods enable precise manipulation of perovskite structures at the nanoscale, offering advantages in optoelectronic applications such as solar cells, light-emitting diodes, and photodetectors. Key approaches include mesoporous scaffolds, block copolymer templates, and colloidal crystallization, each providing unique pathways to tailor perovskite properties.

Mesoporous scaffolds are widely used to guide perovskite growth, particularly in solar cell applications. These scaffolds typically consist of metal oxide frameworks, such as TiO2 or Al2O3, with well-defined pore sizes ranging from 10 to 50 nm. The porous structure serves as a template, confining perovskite crystallization within the pores and reducing grain boundary defects. Infiltration of perovskite precursors into the mesoporous network is achieved through solution processing, followed by thermal annealing to induce crystallization. The scaffold not only directs perovskite growth but also enhances charge transport by providing a conductive pathway. For instance, mesoporous TiO2 scaffolds have been shown to improve the power conversion efficiency of perovskite solar cells by facilitating electron extraction and reducing recombination losses. The pore size and surface chemistry of the scaffold play critical roles in determining perovskite crystallinity and film uniformity. Smaller pores promote nucleation density, leading to finer-grained films, while larger pores allow for more extensive crystal growth. Surface modifications, such as hydroxyl group passivation, can further optimize perovskite infiltration and crystallization kinetics.

Block copolymer templates offer another versatile platform for perovskite self-assembly. These polymers consist of two or more chemically distinct blocks that undergo microphase separation, forming periodic nanodomains with tunable dimensions. By selecting appropriate block ratios and molecular weights, the morphology can be tailored to produce spheres, cylinders, or lamellae with feature sizes between 5 and 100 nm. Perovskite precursors are incorporated into the hydrophilic domains of the copolymer, either through direct blending or selective solvent swelling. Subsequent removal of the polymer template via thermal or chemical treatment yields perovskite nanostructures with controlled geometry. For example, poly(styrene-block-ethylene oxide) copolymers have been used to template perovskite nanowires and quantum dots, exhibiting enhanced photoluminescence quantum yields due to reduced defect states. The block copolymer approach also enables the fabrication of complex architectures, such as gyroidal or double-gyroidal perovskite networks, which are promising for light management in optoelectronic devices. The key challenge lies in achieving complete perovskite infiltration while preserving the template’s structural integrity during processing.

Colloidal crystallization provides a bottom-up route to assemble perovskite nanocrystals into ordered superlattices. Monodisperse perovskite nanocrystals, typically synthesized via hot-injection or ligand-assisted reprecipitation methods, serve as building blocks for hierarchical assembly. By controlling solvent evaporation rates, interfacial interactions, or external fields, these nanocrystals can self-organize into face-centered cubic or hexagonal close-packed arrays. The interparticle spacing and superlattice symmetry are dictated by the nanocrystal size, shape, and surface ligand chemistry. For instance, CsPbBr3 nanocrystals with oleic acid and oleylamine ligands have been assembled into superlattices exhibiting collective optical properties, such as superfluorescence and enhanced charge transport. Colloidal crystallization also allows for the integration of heterostructures, where different perovskite compositions or other nanomaterials are co-assembled to create multifunctional systems. One notable example is the formation of binary superlattices combining CsPbBr3 and CsPbI3 nanocrystals, which exhibit energy transfer and tunable emission spectra. The main advantage of this approach is the ability to precisely engineer the nanocrystal surface chemistry to control assembly kinetics and stability.

A critical aspect of templated perovskite growth is the interplay between the template and the perovskite material. The template’s surface energy, chemical compatibility, and mechanical properties must be carefully matched to the perovskite to ensure uniform nucleation and growth. For instance, hydrophobic templates may require perovskite precursors with modified ligand systems to achieve adequate wetting. Similarly, the thermal expansion coefficients of the template and perovskite must be considered to avoid strain-induced defects during annealing. In mesoporous scaffolds, incomplete pore filling can lead to voids and poor device performance, while excessive precursor loading may cause pore blockage or uncontrolled crystallization outside the scaffold. Block copolymer templates face challenges related to perovskite infiltration depth and domain alignment, particularly for large-area films. Colloidal crystallization must balance the trade-off between nanocrystal stability and superlattice order, as strongly bound ligands can hinder close packing.

Recent advances have explored hybrid templating strategies to combine the benefits of multiple approaches. For example, mesoporous scaffolds functionalized with block copolymers can provide dual confinement effects, enhancing perovskite crystallinity and orientation. Similarly, colloidal nanocrystals have been incorporated into block copolymer matrices to create nanocomposites with tailored optical and electronic properties. These hybrid systems often exhibit synergistic effects, such as improved moisture resistance or enhanced charge carrier mobility, by leveraging the strengths of each templating method.

The choice of templating technique depends on the target application and desired perovskite characteristics. Mesoporous scaffolds are well-suited for photovoltaic devices, where efficient charge transport and minimal defects are paramount. Block copolymer templates excel in creating nanostructured perovskites for light emission or lasing, where quantum confinement and photonic bandgap engineering are critical. Colloidal crystallization is ideal for designing metamaterials or optoelectronic devices requiring precise control over interparticle coupling and collective phenomena.

Future developments in templated perovskite growth will likely focus on scalability, reproducibility, and multifunctionality. Large-area fabrication techniques, such as roll-to-roll processing or spray coating, must be adapted to accommodate templating methods without sacrificing precision. Advances in in situ characterization tools will provide deeper insights into the nucleation and growth dynamics within templates, enabling finer control over perovskite morphology. Additionally, the integration of machine learning for template design and optimization could accelerate the discovery of novel perovskite architectures with tailored properties.

In summary, self-assembly and templated growth techniques represent a sophisticated toolbox for engineering perovskite semiconductors with enhanced performance and functionality. By leveraging mesoporous scaffolds, block copolymer templates, and colloidal crystallization, researchers can manipulate perovskite structures across multiple length scales, unlocking new opportunities for optoelectronic applications. The continued refinement of these methods will be instrumental in overcoming current limitations and realizing the full potential of perovskite-based technologies.