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

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 degrees 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.

Automated summary

This study investigates the nucleation and growth mechanisms during the formation of mixed halide perovskite films using in situ optical microscopy and GISAXS measurements. It was found that the addition of DIO and HI can accelerate nucleation and modify the size of nuclei during growth. These results provide important insights into the crystallization mechanisms and can help improve control over perovskite film formation.