Direct patterning of methylammonium lead bromide perovskites by thermal imprint

Abstract

Promising new materials like solution-processable perovskites may provide devices with superior properties, e.g. for opto-electronics. For some applications patterning is required and nanoimprint as a solvent-free, mechanical shaping process has been identified to be particularly favorable for this purpose. The current investigation refers to the organic–inorganic perovskite methylammonium lead bromide (MAPbBr3) and is related to direct imprint under pressure and temperature. Experiments with a single crystal and polycrystalline layers of differing grain size indicate that a large-grained starting layer offers optimum pre-conditions for the replication of micro/nano-structures. The aim of the present study is to develop a physical understanding of the shaping process with this polycrystalline material. To develop such a conception, analogies between the imprint of polycrystalline perovskites and the imprint of thermoplastic polymers are sought, and the consequences resulting from the differences in the microscopic material response are worked out. The main aspect with perovskites is that plastic deformation occurs due to gliding on crystallographic glide planes, similar to the case of metals. With a < 100 > -oriented perovskite layer the imprint pressure activates a (110) < 110 > -type glide system, providing material transport at 45° with respect to the surface normal. The consequences of this preferential direction are investigated by analyzing experiments with partial and complete filling of the cavities of the stamp used for imprint. By considering the geometric correlations during the initial imprint phase the experimental results can be understood. Beyond that, it turns out that under specific conditions the size and the shape of the grains can be controlled by the imprinted pattern. This ‘grain shaping by patterning’ provides unexpected, innovative prospects for the nanoimprint of perovskite layers.

How the Microstructure of MAPbI3 Powder Impacts Pressure-Induced Compaction and Optoelectronic Thick-Film Properties

“…For crushing and rearrangement processes, powder particles typically break up at sintered connections and move without significantly reducing their crystallite size. In contrast, the crystallite size decreases clearly upon plastic deformation, e.g., due to the formation, movement, and accumulation of dislocations. ,, Here, Mayer et al could also demonstrate recently that plastic deformation in halide perovskites proceeds by gliding of dislocations along well-defined crystallographic planes . Accordingly, when pressing powders with larger particle sizes, the stronger reduction of the crystallite size (Table ) indicates that the larger particles exhibit more plastic deformation.…”

Nanopatterning of Perovskite Thin Films for Enhanced and Directional Light Emission

“…Polarization in lighting could be relevant to reduce glare, e.g., in car-headlight situations. Several mask-free (e.g., inkjet and e-jet printing, laser-assisted patterning, laser ablation) and mask-assisted (e.g., nanoimprint, template-confined patterning by photolithography) methods have been employed to obtain periodically structured substrates. − However, only a few strategies have been successfully applied to perovskite layers. − Despite the many potential routes for obtaining periodically patterned perovskites, the fabrication of perovskite LEDs with custom angular emission properties remains challenging, as this would require both flexibility in the design of the periodic structures, precision in the fabrication, and scalability of the approach. In principle, imprinting the perovskite directly using a polydimethylsiloxane (PDMS) mold would fulfill these requirements.…”