Tunable
Crystallization and Nucleation of Planar CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> through Solvent-Modified Interdiffusion
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Abstract
A smooth
and compact light absorption perovskite layer is a highly desirable
prerequisite for efficient planar perovskite solar cells. However,
the rapid reaction between CH<sub>3</sub>NH<sub>3</sub>I methylammonium
iodide (MAI) and PbI<sub>2</sub> often leads to an inconsistent CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> crystal nucleation and growth
rate along the film depth during the two-step sequential deposition
process. Herein, a facile solvent additive strategy is reported to
retard the crystallization kinetics of perovskite formation and accelerate
the MAI diffusion across the PbI<sub>2</sub> layer. It was found that
the ultrasmooth perovskite thin film with narrow crystallite size
variation can be achieved by introducing favorable solvent additives
into the MAI solution. The effects of dimethylformamide, dimethyl
sulfoxide, γ-butyrolactone, chlorobenzene, and diethyl ether
additives on the morphological properties and cross-sectional crystallite
size distribution were investigated using atomic force microscopy,
X-ray diffraction, and scanning electron microscopy. Furthermore,
the light absorption and band structure of the as-prepared CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films were investigated and
correlated with the photovoltaic performance of the equivalent solar
cell devices. Details of perovskite nucleation and crystal growth
processes are presented, which opens new avenues for the fabrication
of more efficient planar solar cell devices with these ultrasmooth
perovskite layers