Influence of Additives on the In Situ Crystallization Dynamics of Methyl Ammonium Lead Halide Perovskites

Abstract

Understanding the kinetics of the crystallization process for organometal halide perovskite formation is critical in determining the crystalline, nanoscale morphology and therefore the electronic properties of the films produced during thin film formation from solution. In this work, in situ grazing incidence small-angle X-ray scattering (GISAXS) and optical microscopy measurements are used to investigate the processes of nucleation and growth of pristine mixed halide perovskite (MAPbI 3– x Cl x ) crystalline films deposited by bar coating at 60 °C, with and without additives in the solution. A small amount of 1,8-diiodooctane (DIO) and hydriodic acid (HI) added to MAPbI 3– x Cl x is shown to increase the numbers of nucleation centers promoting heterogeneous nucleation and accelerate and modify the size of nuclei during nucleation and growth. A generalized formation mechanism is derived from the overlapping parameters obtained from real-time GISAXS and optical microscopy, which revealed that during nucleation, perovskite precursors cluster before becoming the nuclei that function as elemental units for subsequent formation of perovskite crystals. Additive-free MAPbI 3– x Cl x follows reaction-controlled growth, in contrast with when DIO and HI are present, and it is highly possible that the growth then follows a hindered diffusion-controlled mechanism. These results provide important details of the crystallization mechanisms occurring and will help to develop greater control over perovskite films produced.

A Systematic Review of Metal Halide Perovskite Crystallization and Film Formation Mechanism Unveiled by In Situ GIWAXS

“…[114] Besides Yoneda peak shift, perovskite nucleation and growth processes were also studied by Dunbar et al by fitting GISAXS data with a power-law model, demonstrating faster nucleation with the addition of HI and DIO additives. [115] The slope of the power-law scattering curves was related to the surface fractal dimension. [116] Lin et al, therefore, found that the surface roughness of perovskite films can become larger along with annealing owing to the increased surface fractal dimension, which explained the variation in resulted device performance.…”

Time‐Resolved Orientation and Phase Analysis of Lead Halide Perovskite Film Annealing Probed by In Situ GIWAXS

“…[ 46 ] Also, depth‐dependent measurements can be done on, for example, crystallization direction and depth‐dependent crystal orientation was investigated during perovskite spin‐coating. [ 47 ] Today, typically one thin‐film deposition method is in the focus of such in situ studies, [ 48–50 ] while direct comparisons are scarce. However, such comparisons are essential to learn about fundamental differences between various deposition techniques and to accelerate knowledge transfer from the lab toward commercialization.…”

The Contribution of NMR Spectroscopy in Understanding Perovskite Stabilization Phenomena

“…The “soft” nature of perovskites is, in fact, characterized by ion conduction and ion migration [ 41 ], with the drawback of the instability of the perovskite, especially under operation conditions (light, moisture, heat) [ 42 ], as well as hysteresis in the devices due to the ion vacancies acting as charge traps [ 43 ]. Therefore, the use of additives firstly improves the crystal growth [ 44 ], and then the device performances and the long-term stability [ 45 ]. However, not all additives are able to blend with the perovskite precursors with the same good effects.…”