Kinetic-Controlled Crystallization of α-FAPbI3 Inducing Preferred Crystallographic Orientation Enhances Photovoltaic Performance

Crystallization kinetic controls the crystallographic orientation, inducing anisotropic properties of the materials. As a result, preferential orientation with advanced optoelectronic properties can enhance the photovoltaic devices' performance. Although incorporation of additives is one of the most studied methods to stabilize the photoactive alpha-phase of formamidinium lead tri-iodide (alpha-FAPbI(3)), no studies focus on how the additives affect the crystallization kinetics. Along with the role of methylammonium chloride (MACl) as a stabilizer in the formation of alpha-FAPbI(3), herein, the additional role as a controller in the crystallization kinetics is pointed out. With microscopic observations, for example, electron backscatter diffraction and selected area electron diffraction, it is examined that higher concentration of MACl induces slower crystallization kinetics, resulting in larger grain size and [100] preferred orientation. Optoelectronic properties of [100] preferentially oriented grains with less non-radiative recombination, a longer lifetime of charge carriers, and lower photocurrent deviations in between each grain induce higher short-circuit current density (J(sc)) and fill factor. Resulting MACl40 mol% attains the highest power conversion efficiency (PCE) of 24.1%. The results provide observations of a direct correlation between the crystallographic orientation and device performance as it highlights the importance of crystallization kinetics resulting in desirable microstructures for device engineering.

Automated summary

Crystallization kinetics control crystallographic orientation and result in anisotropic properties of materials. Preferential orientation with advanced optoelectronic properties enhances the performance of photovoltaic devices. This study investigates the role of methylammonium chloride (MACl) as a stabilizer and a controller in the crystallization kinetics of formamidinium lead tri-iodide (alpha-FAPbI(3)). It is found that higher MACl concentration leads to slower crystallization kinetics, larger grain size, and [100] preferred orientation, resulting in improved device performance such as higher short-circuit current density and fill factor. A MACl concentration of 40 mol% achieves the highest power conversion efficiency of 24.1%.