Understanding on the formation mechanisms of quasi-2D Ruddlesden- Popper halide perovskites

Two dimensional (2D) or quasi-2D halide perovskites have attracted intense interest in recent years for the replacement of three dimensional(3D) perovskites, owing to their stability and structural/optoelectronic tunability. However, the control of their composition and orientation is challenging when solution processed for thin films, because of the similarity in formation energy for different layer numbers. In this review, we discuss the factors affecting formation of 2D and quasi 2D perovskites, especially Ruddlesden-Popper perovskites, in solution-processed thin films. All the factors are associated with nucleation and growth kinetics, which affect their phase distribution and orientation. Furthermore, the performances of the photovoltaics and light-emitting diodes based on the controlled quasi-2D perovskites are briefly discussed.