First-Principles Study of Novel Two-Dimensional (C₄H₉NH₃)₂PbX₄ Perovskites for Solar Cell Absorbers

Low-dimensional perovskites (A₂BX₄), in which the A cations are replaced by different organic cations, may be used for photovoltaic applications. In this contribution, we systematically study the two-dimensional (2D) (C₄H₉NH₃)₂PbX₄ (X═Cl, Br and I) hybrid perovskites by density functional theory (DFT). A clear structures-properties relationship, with the photophysical characteristics directly related to the dimensionality and material compositions, was established. The strong s-p antibonding couplings in both bulk and monolayer (C₄H₉NH₃)₂PbI₄ lead to low effective masses for both holes (m_h*) and electrons (m_e*). However, m_h* increases in proportion to the decreasing inorganic layer thickness, which eventually leads to a slightly shifted band edge emission found in 2D perovskites. Notably, the 2D (C₄H₉NH₃)₂PbX₄ perovskites exhibit strong optical transitions in the visible light spectrum, and the optical absorption tunings can be achieved by varying the compositions and the layer thicknesses. Such work paves an important way to uncover the structures-properties relationship in 2D perovskites.