Role of the spacer cation in the growth and crystal orientation of two-dimensional perovskites
Two-dimensional metal halide perovskites are being immensely investigated because of the structural diversity and stability offered by this vast family of materials. Many efforts have been devoted to the use of these materials in diverse applications by tuning the optical band gap. The key parameter that needs to be controlled for efficient charge transport in two-dimensional perovskites is the crystal orientation. In this review, we first discuss the mechanisms of crystal formation and crystal growth to obtain the preferred vertical orientation. Next, the impact of organic spacer cations on controlling the growth and crystal orientation of 2D thin films will be discussed based on some of the strategies that allow optimizing these features such as compositional engineering, processing engineering, additive engineering, and the effect of solvent and temperature. At the end, the current challenges and future perspectives are proposed.