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The Urbach energy as a measure of energetic disorder is an important characteristic of semiconductors to evaluate their optoelectronic functionality. However, discrepancies occur in Urbach energy values EUdetermined via different measurement and analysis methods, whose origin of a profound understanding is still missing. To reliably analyze the origin of such discrepancies, we recorded quasi-simultaneously temperature-dependent absorption and photoluminescence (PL) spectra of halide perovskite (MAPbI3) thin-film and single-crystal samples. Performing profound Urbach analyses in an extended energy range down to 0.2 eV below the bandgap, we find energy-range-dependent exaggeration effects on Urbach energy values to be only present in the near bandgap region (∼0.02 eV below the bandgap), where non-Urbach absorption states start to contribute. Besides that, generally lower EUvalues and a lower temperature-dependence of EUare obtained from PL than from absorption, which originates from the sensitivity of PL for sites with lower energetic disorder and/or higher phonon energies in the excited-state geometry. Thus, our work is sensitized to proper interpretation and comparison of EUvalues and contributes to developing a more fundamental understanding of semiconductor materials.

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.