Progresses and Challenges with Two-Dimensional Halide Perovskite Photovoltaics

Abstract

While numerous research groups have contributed to significant advancement of three-dimensional (3D) halide perovskites for use in photovoltaic applications, the number of publications reporting the development and fundamental properties of the materials of lower dimensionalities remains relatively small. Two-dimensional (2D) hybrid metal halide perovskites possessing the general chemical formulas (RNH3)2MX4 and (NH3RNH3)MX4 (R corresponds to an organic functional group, M a group 14 metal dication, and X a halide) are derived from their 3D congeners by slicing the inorganic lattice along specific crystallographic axes (e.g., the (100)- or (110)-planes). This can be induced through incorporation of moderately sized organic cations, such as 2-phenylethylammonium and 1-butylammonium, and it yields alternating 2D layers of organic cations and single Pb-atom-thick inorganic lattices. These are referred to as n = 1 2D hybrid metal halide perovskites, where n refers to the number of contiguous 2D inorganic layers, i.e., not separated by organic cations. The resulting 2D materials possess synthetic versatility and moisture stability greater than that of pure 3D perovskites. However, they are, generally, considered ill-suited for photovoltaic applications because their reduced dimensionality manifests in poor charge transport and compromised visible light absorption. In addition, they typically possess high excitonic binding energy values as a result of the dielectric mismatch between the organic and inorganic constituents. In this talk, I will present and review the factors that control the performance of n = 1 2D halide perovskite photovoltaics, including the judicious choice of organic and group 14 metal cations and selection of charge-transport materials that are compatible with perovskite layers. Key challenges and potential pathways for achieving efficient solar cells will then be identified and discussed.