Tomasz Marszalek

Heterogeneous crystallization kinetics critically govern the morphology and performance of solution-processed semiconductors, yet morphology control is often achieved through trial-and-error optimization. Quantitative understanding of crystallization is essential for precise morphology control but is limited by the simultaneous occurrence of heterogeneous nucleation and crystal growth. Here, a time-defined induced nucleation strategy has been developed to initiate crystallization at specific stages of solution processing. Systematic variation of nucleation timing reveals three distinct morphological regimes, whose emergence is explained by the concentration-dependent critical cluster radius in bulk, interfacial, and cusp environments. On this basis, a quantitative, dimensionless model is developed for heterogeneous crystallization kinetics across diverse processing conditions. The model demonstrates universality across perovskite and organic semiconductors. In situ studies reveal identical growth kinetics for induced and spontaneous nuclei, validating its generality. The resulting morphology control enables tuning of crystallinity and charge transport in solution-processed transistors.

Dion-Jacobson (DJ) phase perovskites are increasingly recognized as potential semiconductor materials for electronic applications. However, the restricted coordination between the organic diammonium cations and the inorganic framework inhibits their self-assembly into efficient DJ Sn-based perovskites during solution processing. This study introduces solvent vapor assisted drop casting (SVAD) as a novel processing method to favor the organization into highly crystalline DJ perovskite films. The key aspect of the processing is the extended crystallization time in solvent vapor at elevated temperature. The processing study was conducted on four DJ perovskites that varied in the rigidity and symmetry of their A-cations to demonstrate the universal applicability of SVAD for this category of semiconductors and to establish correlations between structure and properties. The SVAD films exhibit markedly improved crystallinity and morphology compared to spin-coated samples resulting in significantly increased local and device charge carrier mobilities. DJ perovskites with rigid and symmetric A-cations form a planar [SnI₆]^4– octahedral framework that favors structural order and charge carrier transport. This work paves the way for the solution processing of highly ordered DJ Sn-based perovskites for their implementation in electronic applications.

The charge carrier transport properties of two-dimensional benzimidazolium tin iodide perovskite ((Bn)₂SnI₄) show a hopping mechanism for macroscopic transport and a band mechanism on the nanoscopic scale.

Oscillations in the chemical or physical properties of materials, composed of an odd or even number of connected repeating methylene units, are a well-known phenomenon in organic chemistry and materials science. So far, such behavior has not been reported for the important class of materials, perovskite semiconductors. This work reports a distinct odd-even oscillation of the molecular structure and charge carrier transport properties of phenylalkylammonium two-dimensional (2D) Sn-based perovskites in which the alkyl chains in the phenylalkylammonium cations contain varying odd and even carbon numbers. Density functional theory calculations and grazing-incidence wide-angle X-ray scattering characterization reveal that perovskites with organic ligands containing an alkyl chain with an odd number of carbon atoms display a disordered crystal lattice and tilted inorganic octahedra accompanied by reduced mobilities. In contrast, perovskites with cations of an even number of carbon atoms in the alkyl chain form more ordered crystal structures, resulting in improved charge carrier mobilities. Our findings disclose the importance of minor changes in the molecular conformation of organic cations have an effect on morphology, photophysical properties, and charge carrier transport of 2D layered perovskites, showcasing alkyl chain engineering of organic cations to control key properties, of layered perovskite semiconductors.

Two-dimensional (2D) tin halide perovskites are promising semiconductors for field-effect transistors (FETs) owing to their fascinating electronic properties. However, the correlation between the chemical nature of organic cations and charge carrier transport is still far from understanding. In this study, the influence of chain length of linear alkyl ammonium cations on film morphology, crystallinity, and charge transport in 2D tin halide perovskites is investigated. The carbon chain lengths of the organic spacers vary from propylammonium to heptanammonium. The increase of alkyl chain length leads to enhanced local charge carrier transport in the perovskite film with mobilities of up to 8 cm² V⁻¹ s⁻¹, as confirmed by optical-pump terahertz spectroscopy. A similar improved macroscopic charge transport is also observed in FETs, only to the chain length of HA, due to the synergistic enhancement of film morphology and molecular organization. While the mobility increases with the temperature rise from 100 K to 200 K due to the thermally activated transport mechanism, the device performance decreases in the temperature range of 200 K to 295 K because of ion migration. These results provide guidelines on rational design principles of organic spacer cations for 2D tin halide perovskites and contribute to other optoelectronic applications.

Meniscus‐guided coating (MGC) is a promising method that offers predictable fabrication of highly crystalline thin films. For the integration of molecular semiconductors into large‐area electronic devices with high efficiency and reliability, homogeneous and highly ordered film morphologies are required. The solution processing of such defect‐free film structures requires comprehensive understanding of the complex relationship between molecular crystallization, fluid dynamics, and meniscus shape. In this work, the role of the meniscus shape on fluid dynamics in the coating bead and the crystallization process of the low molecular weight semiconductor 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐pentacene) during zone‐casting is systematically investigated. Depending on meniscus shape and coating velocity, four morphological subregimes are found: stick‐slip morphology, unidirectional homogenous crystal stripes, spherulitic morphology, and directional branched morphology; of which the second exhibits the highest crystallinity with a reduced trap density in the thin film, resulting in improved saturation and effective mobilities in field‐effect transistors (FET). Numerical simulation of fluid dynamics explains the observed morphological trends, which are correlated with the electrical behavior of the devices. This work provides a fundamental basis for upscaling MGC methods for the application of functional thin films.

Understanding and controlling the nucleation and crystallization in solution‐processed perovskite thin films are critical to achieving high in‐plane charge carrier transport in field‐effect transistors (FETs). This work demonstrates a simple and effective additive engineering strategy using pentanoic acid (PA). Here, PA is introduced to both modulate the crystallization process and improve the charge carrier transport in 2D 2‐thiopheneethylammonium tin iodide ((TEA)₂SnI₄) perovskite FETs. It is revealed that the carboxylic group of PA is strongly coordinated to the spacer cation TEAI and [SnI₆]⁴⁻ framework in the perovskite precursor solution, inducing heterogeneous nucleation and lowering undesired oxidation of Sn²⁺ during the film formation. These factors contribute to a reduced defect density and improved film morphology, including lower surface roughness and larger grain size, resulting in overall enhanced transistor performance. The reduced defect density and decreased ion migration lead to a higher p‐channel charge carrier mobility of 0.7 cm² V⁻¹ s⁻¹, which is more than a threefold increase compared with the control device. Temperature‐dependent charge transport studies demonstrate a mobility of 2.3 cm² V⁻¹ s⁻¹ at 100 K due to the diminished ion mobility at low temperatures. This result illustrates that the additive strategy bears great potential to realize high‐performance Sn‐based perovskite FETs.

Controlling crystal growth and reducing the number of grain boundaries are crucial to maximize the charge carrier transport in organic–inorganic perovskite field-effect transistors (FETs). Herein, the crystallization and growth kinetics of a Sn(II)-based 2D perovskite, using 2-thiopheneethylammonium (TEA) as the organic cation spacer, were effectively regulated by the hot-casting method. With increasing crystalline grain size, the local charge carrier mobility is found to increase moderately from 13 cm² V⁻¹ s⁻¹ to 16 cm² V⁻¹ s⁻¹, as inferred from terahertz (THz) spectroscopy. In contrast, the FET operation parameters, including mobility, threshold voltage, hysteresis, and subthreshold swing, improve substantially with larger grain size. The optimized 2D (TEA)₂SnI₄ transistor exhibits hole mobility of up to 0.34 cm² V⁻¹ s⁻¹ at 295 K and a higher value of 1.8 cm² V⁻¹ s⁻¹ at 100 K. Our work provides an important insight into the grain engineering of 2D perovskites for high-performance FETs.