Ala'a O. El-Ballouli, Osman M. Bakr, and Omar F. Mohammed
The Journal of Physical Chemistry Letters, (2020)
Two-dimensional (2D) layered metal halide perovskites are potential alternatives to three-dimensional (3D) perovskites in optoelectronic applications owing to their more pronounced photostabilities and chemical stabilities. Recent experimental and theoretical investigations of 2D metal-halide perovskites have demonstrated interesting optical and electronic properties of various structures that are controlled not only by their elemental composition but also by utilizing different organic spacers. However, photovoltaic devices that utilize 2D metal halide perovskites suffer from poor device efficiency due to inefficient charge carrier separation and extraction. This is mainly because quantum and dielectric confinements in 2D perovskites lead to strongly bound excitons. In this Perspective, we shed light on confinement-control and structural-variation strategies that provide better parameters for the efficient collection of charges in 2D metal halide perovskites. The influence of these strategies on the exciton binding energies, charge-carrier mobilities, hot-carrier dynamics and extraction, and electron-phonon coupling in 2D metal halide perovskites is thoroughly discussed, as these parameters highlight unique opportunities for further system optimization and dictate the efficacy of the materials as light absorbers in photovoltaics. Beyond the tunability of these fundamental parameters, we conclude this Perspective with the most notable strategies for attaining 2D perovskites with reduced bandgaps to better suit solar cell applications.