Toward Tailored Film Morphologies: The Origin of Crystal Orientation in Hybrid Perovskite Thin Films

Efficient perovskite solar cells can be produced by a wide variety of different methods. Previous results show that controlling the film morphology is critical to enhance the efficiency of the prepared devices. Here, grazing-incidence wide-angle X-ray scattering (GIWAXS) is used to study the morphology and especially the orientation distribution of CH₃NH₃PbI₃ (MAPI) perovskite films prepared by five typical methods. We find that the investigated one-step methods produce non-oriented films, while the two-step deposition methods produce varying degrees of orientation depending on the method chosen to convert the highly oriented PbI₂ precursor, providing direct evidence for different perovskite conversion mechanisms. In particular, we show that the morphology and crystal orientation of MAPI films is tunable by varying the spin-coating temperature and by adding chloride to the conversion solution. By relating the precursor morphology to the resulting MAPI film morphology, we link the observed preferential orientations to specific conversion mechanisms, thereby establishing GIWAXS as an important tool toward a rational development of new synthesis methods.