Organometal halide perovskites are promising materials for photovoltaic devices and have demonstrated a rapid increase in performance in the last decade. Recently, perovskite solar cells have passed the threshold of 20 % power conversion efficiency (PCE) by optimized processing and device structures. Despite the high PCE, perovskite solar cells are still not competitive to their inorganic counterparts in terms of production scalability and lifetime.

Most of the devices reported in literature are fabricated by small-scale solution-based processing techniques (e.g. spin-coating). Perovskite solar cells produced by vacuum thermal evaporation (VTE) have also been attracting considerable attention, due to uniformly deposited layers, high PCE and reproducibility. Regarding the co-evaporation of the perovskite constituents, this technology is challenged by large differences in thermodynamic characteristics of the two species. While the organic components evaporate instantaneously, higher temperatures are needed for reasonable deposition rates of the metal halides. An option to overcome the mentioned issues are vapor phase based processes, which have been proven to be a desirable choice for industrial large-area production. 

In this study, we present a setup for the deposition of methylammonium lead iodide (MAPbI₃) via chemical vapor deposition employing nitrogen as carrier gas. Therefore, we developed evaporation sources for temperatures up to 500 °C in case of lead iodide and 150 °C for methylammonium iodide. The deposition rates can be easily controlled by adjusting carrier gas flows. In the pressure regime of 10 – 20 mbar, the deposition of the perovskite layer is carried out on 2.5 cm x 2.5 cm large either fluorine-doped tin oxide on glass or silicon substrates involving a reaction of both co-deposited components. The substrate can be heated or cooled to control layer formation and reaction kinetics. We discuss the impact of the simultaneous and alternating deposition of the precursors on the resulting films and point out the effect of the substrate temperature on the structural properties. X-Ray diffraction measurements are used to verify perovskite formation. In order to investigate the crystal quality and structural properties scanning electron microscopy is carried out.

By optimizing the deposition parameters, we produced uniform perovskite films at a deposition rate of 30 nm/h. Furthermore, the developed CVD process can be easily scaled up to larger substrates, thus rendering this technique a promising candidate for manufacturing large-area devices. Moreover, CVD of perovskite solar cells can overcome most of the limitations of liquid processing, e.g. the need for appropriate and orthogonal solvents.