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.