Metal halide perovskites are a highly promising class of semiconductors for the fabrication of cheap and efficient optoelectronic devices such as solar cells, LED’s, and photodetectors. Intense research effort has resulted in efficiencies for lab scale perovskite solar cells of over 25%. [1] More recently perovskite solar cells are also attracting a lot of commercial interest which is increasing the importance of factors such as long-term stability, processability at a large scale, and cost. Co-evaporation is a promising deposition technique for the upscaling of perovskites because it is additive, results in very uniform films, and does not require toxic solvents [2].

Recently two-dimensional organic metal halide materials which are similar to the well-known 3D perovskites have attracted a lot of attention. They are frequently called 2D perovskites, even so they do not possess a perovskite structure. Long organic molecules are used on the A site which are too big to be incorporated into the perovskite structure and a layered structure forms instead. These 2D materials are promising as stabilisation and passivation layers used together with 3D perovskites or for use on their own as active materials in LEDs and solar cells.

It has previously been shown by La-Placa et al. [3] that it is also possible to co-evaporate 2D metal halide semiconductors and integrate them into solar cells. Unfortunately, La-Placa et al. also found that the 2D layers can hinder charge transport in the device and while they may be helpful for the overall stability, they did not improve the solar cell efficiency. The orientation of the 2D sheets is crucial for the charge transport through the 2D layer. Being able to determine and ideally influence that orientation is therefore decisive for usability of these films in efficient devices.

In this study we co-evaporate PEA₂PbI₄ (phenethyl ammonium lead iodide) 2D metal halide thin films. We probe their properties in detail using electron microscopy, GIWAXS, and optical measurements. We find that using evaporation, it is possible to fabricate very uniform, planar, pin-hole free thin-films. Using GIWAXS measurements we probe the details of the texture and orientation in these films and how they are influenced by fabrication conditions. Understanding the direction of and degree of orientation in these films is an important step towards being able to influence the orientation which will be crucial for the integration of 2D metal halide perovskites into devices such as LEDs and solar cells.