Predicting the Morphology of Perovskite Thin Films Produced by Sequential Deposition Method: A Crystal Growth Dynamics Study

Abstract

We performed a kinetic analysis of the sequential deposition method (SDM) to investigate how to form perovskite (CH 3 NH 3 PbI 3 ) phases, and the effects of processing conditions on the final perovskite morphology. The reaction was found to consist of two periods with distinct kinetics. During the first period, perovskite crystals nucleated on the lead iodide (PbI 2 ) surface, and the reaction proceeded until the surface was completely converted to perovskites. The reaction during this period determined the surface morphology of the perovskites. We were able to extract the value of the rate of the phase transformation during the first period by applying the Johnson−Mehl−Avrami−Kolmogorov model, in which the rate r is related to the average grain size R by R ∝ r −1/3 . In this way, r was used to predict the surface morphology of the perovskite under certain processing conditions. During the second period, the remaining lead iodide under the top perovskite layer was converted. Methylammonium iodide (CH 3 NH 3 I, MAI) molecules apparently diffused into the buried PbI 2 through intergrain gaps of the top perovskite layers. Added MAI molecules reacted with PbI 2 but also generated single-crystal perovskite nanorods, nanoplates, and nanocubes. The current study has furthered the understanding of detailed features of the SDM, enabled a reliable prediction of the final perovskite morphology resulting from specified processing conditions, and contributed to a reproducible fabrication of high-quality perovskite films.

Stable, High‐Sensitivity and Fast‐Response Photodetectors Based on Lead‐Free Cs2AgBiBr6 Double Perovskite Films

“…The results are in good agreement with the obviously increased intensity of the main diffraction peaks of (200) and (400) at 15.71° and 31.76° from the XRD patterns (Figure e), suggesting the improved crystallinity or orientation of the obtained double perovskite films. As we observe much worse solubility of the double perovskite single crystals in DMF (Figure S1, Supporting Information), we anticipate that the introduced DMF reduces the nucleation sites and promotes the Ostwald ripening of the crystals during the film formation, which is consistent with previously demonstrated crystal growth process of lead halide perovskites . We observe the appearance of some bright areas from the SEM images when we further increase the DMF ratio to 20% (Figure d).…”

Strategies to Improve Luminescence Efficiency of Metal‐Halide Perovskites and Light‐Emitting Diodes

“…Two‐step solution process can also achieve uniform MHP films, because in this process nucleation is the main crystallization mechanism rather than growth of crystals . FAPbBr 3 films coated using the two‐step solution process showed uniform films with γ rms < 20 nm and small grain size (100 – 200 nm) and achieved moderate EL efficiency in PeLEDs (EQE ≈ 1.16%, CE ≈ 2.65 cd A −1 ) .…”

Gas flow-assisted vacuum drying: identification of a novel process for attaining high-quality perovskite films

“…As such, the vacuum drying mechanism can be explained by the LaMer crystallization and nucleation theory: Fast solvent evaporation under vacuum conditions lead to an oversaturated film with a high nucleation density from which the perovskite crystals grow more homogenous compared to a slower drying film with fewer seed nuclei and irregular growth conditions without vacuum assistance. [21][22][23][24][25] Moreover, despite the fact that several studies report that an additional gas flow influences the halide formation, little or no consideration is given to the use of venting of the chamber in the context of MHP formation using vacuum drying processes. 26,27 An elegant method to elucidate the film formation of MHPs is optical in situ monitoring.…”