2D-3D Graded Perovskites: from Film Formation to Optoelectronic Devices

Quasi-2D perovskites are promising candidates for stable and efficient optoelectronic devices, such as light-emitting diodes, solar cells, and photodiodes. On top of superior environmental stability compared to their 3D counterpart, they possess versatile optoelectronic properties. In fact, by varying the number of inorganic layers sandwiched between the organic spacers (n), bandgap and exciton binding energy can be tuned. During film deposition, however, a variety of structural phases with different n-values are formed, usually making a 2D-3D gradient where lower dimensional phases are located at the bottom of the film and 3D at the top.

Chasing phase purity has been a challenging task for researchers, as both kinetics and thermodynamics play an important role in determining which phases are formed. While solvent engineering has been used to tune phase purity, no reports have investigated the effect of co-solvents on the crystallization mechanism of quasi-2D perovskites and their impact on phase distribution. To fill this gap, we first investigated the kinetics of film formation of quasi-2D perovskites in presence of co-solvents. By using such a solvent engineering approach and in-situ techniques, we explained the mechanism behind 2D-3D gradient formation and how to selectively tune it.

We then employed 2D-3D graded perovskites for a variety of applications. First, to investigate the dependence of halide segregation in mixed-halide perovskites on their dimensionality. By forming such a multidimensional film, we could in fact study the photostability under illumination of both 2D, quasi-2D, and 3D perovskites. Then, to enhance the performances of perovskite photodiodes, which we found to be strongly dependent on a thermal charge generation mechanism taking place at the interface between the electron-blocking and the active layer.