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Organic-inorganic halide perovskite (OIHP) thin films at the heart of the new perovskite solar cells (PSCs) are very brittle, limiting the mechanical reliability of PSCs. Here we show that fine-grained MAPbI 3 (prototypical OIHP) films with grain size (~290 nm) smaller than the typical film thickness (~500 nm) tend to fracture intergranularly, resulting in low toughness (0.41 J.m−2). In contrast, MAPbI 3 /substrate interfacial fracture occurs in films with grains larger (~730 nm) than the film thickness, resulting in much higher toughness (1.14 J.m−2). Thus, coarse-grained OIHP films are deemed desirable for not only improved PSCs performance and stability but also mechanical reliability. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Organic–inorganic halide perovskite (OIHP) thin films at the heart of the burgeoning thin-film perovskite solar cells (PSCs) technology possess poor mechanical properties, which is likely to limit the long-term reliability of PSCs as they are poised for commercialization. In an effort to address this issue, here we demonstrate that through-thickness cracks induced by bending-tension in thin films of the two prototypical OIHPs, methylammonium lead triiodide (MAPbI 3) and formamidinium lead triiodide (FAPbI 3), can be healed easily. This is through the application of either a moderate compressive stress (bending-compression) at room temperature or a simple heat-treatment at modest temperatures. The crack-healing process is found to be time-dependent, which indicates that facile mass-transport in OIHPs plays a key role in this phenomenon. An explanation for this phenomenon is provided, one based on the fundamentals of brittle fracture. This discovery has broad implications for the prevention and/or restoration of the overall performance, environmental stability, and mechanical reliability of PSCs, and other devices. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Organic-inorganic halide perovskites (OIHPs) are a remarkable family of hybrid materials at the heart of the emerging thin-film perovskite solar cells (PSCs) technology and other applications. In this Viewpoint article, in addition to some original experimental results, thermo-mechanical analyses of residual macro- and micro-stresses in OIHP thin films are presented in the context of fracture of both the OIHP layer itself and its interface with the substrate. The implications of mechanical behavior of OIHPs and interfaces on the reliability of PSCs, as well as opportunities for future research directions in this general area, are highlighted. [ABSTRACT FROM AUTHOR]

The lineal-intercept method is commonly used to estimate the average grain size, where the 'Mendelson' multiplying factor (1.60) that is typically used explicitly assumes tetrakaidecahedral grains. While this is appropriate for bulk equiaxed microstructures, grains in thin films where the grain size exceeds the film thickness, are closer to prismatic polyhedrons in shape. Thus, assuming log-normal distribution of hexagonal-prism-shaped grains, a new multiplying factor of 1.20 is derived which relates the average grain size and measured intercept size. This model is successfully validated using experimental measurements of three different coarse-grained thin films of halide perovskites used in solar cells. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract: The sol–gel process was employed to prepare (Pb1−x La x )(Zr1−y Ti y )O3 (PLZT) ceramics with nominal composition (Pb0.92La0.08)(Zr0.60Ti0.40)O3. X-ray diffraction results showed that the perovskite PLZT phase is formed at room temperature itself. The average size distribution of the particles was obtained by small angle X-ray scattering (SAXS). Nano-crystalline particles with a size of the order of ∼30nm were found. Morphological studies were carried out by SEM analyses to observe the grain structure. TG–DTA and DSC studies were used to analyze the thermal properties of the nano-powders, in order to understand the reaction kinetics in them. Poled bulk ceramic samples prepared from the sol–gel derived powders were subjected to electrical measurements, in order to determine the piezoelectric and electromechanical coupling coefficients. [Copyright &y& Elsevier]