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In recent years, record efficiencies of halide perovskite-based devices have been achieved by processing high-quality thin films, where small morphology differences seem to be relevant for optimized optoelectronic functionality. However, a detailed understanding on how small morphological changes in perovskite films affect their structural and optoelectronic properties is still missing. Here, we investigate the influence of small morphology differences (i.e., increased grain size and crystallographic orientation), which are induced by hot-pressing methylammonium lead iodide (MAPbI3) thin films, on the structural properties, phase transition behavior, energetic disorder, and defects. To this end, detailed temperature-dependent photoluminescence (PL) and absorption analyses from 300 K down to 5 K are performed. The morphology differences, confirmed by scanning electron microscopy and X-ray diffractometry analyses, result in an increased phase transition temperature for hot-pressed (HP) films, which we attribute to less strain. Moreover, fluence-dependent and transient PL measurements reveal a lower defect density in HP films. Here, besides grain size, also the degree of orientation appears to enhance the charge carrier lifetimes. The identified interdependence of strain and defect properties with film morphology suggests small differences in the perovskite’s energetic disorder. Our work thus emphasizes the importance that even small structural differences in halide perovskites have on their optoelectronic functionality, spurring their further optimization.

Within the last few years, applying pressure to improve and alter the structural and optoelectronic properties of halide perovskite thin films and powder-based thick-film pellets has emerged as a promising processing method. However, a detailed understanding of the relationship between perovskite microstructure, pressing process, and final film properties is still missing. Here, we investigate the impact of powder microstructure on the compaction processes during pressure treatment and on the final properties of powder-pressed thick films, using the model halide perovskite methylammonium lead iodide (MAPbI3). Analyzing pressure relaxations together with XRD and SEM characterizations, we find that larger powder particles result in less compact thick films with higher surface roughness. Furthermore, larger particles exhibit stronger sintered connections between individual powder particles, resulting in less crushing and particle rearrangement but in more pronounced plastic deformation during pressure treatment. Moreover, plastic deformation of the powder particles leads to a reduction of crystallite size in the final film. This reduction results in increased nonradiative, defect-associated excited state recombination, as confirmed by photoluminescence investigations. More plastic deformation also deteriorates the grain boundary quality and consequently facilitates ion migration, which is reflected in higher electrical dark conductivities of the thick films. Thus, our work elucidates how important the design of the perovskite powder microstructure is for the pressure-induced compaction behavior and for the resulting structural, optical, and electrical thick-film properties. These insights will pave the way for tailored pressure processing of halide perovskite films with improved optoelectronic properties.