Spacer Cation Engineering of Two-Dimensional Hybrid Perovskites with Tunable Band Alignment and Optoelectronic Properties

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Band alignment between the organic and inorganic layers in two-dimensional (2D) hybrid perovskites inherently determines their carrier spatial confinement and charge separation, which is of great importance for optoelectronic applications. However, 2D perovskites usually exhibit type I band alignment with large exciton binding energies, making them difficult to be applied in photovoltaic devices and photodetectors. Here we report the spacer cation engineering of 2D hybrid lead iodine perovskites (HLIPs) for achieving tunable band alignments and improved optoelectronic properties based on density functional theory (DFT) calculations. Our calculated results indicate that the electronic structures and carrier spatial distribution of 2D HLIPs can be tuned by incorporating appropriate spacer organic cations. Furthermore, (DPA) 2 (MA) n −1 Pb n I 3 n +1 has been found as a class of promising 2D HLIPs with the type II band alignment, optimal band gaps (1.54–1.96 eV), and large absorption coefficients (>10 5 cm –1 ) in the visible region, which makes their high power conversion efficiency (PCE) up to 22% predicted by a developed PCE model. This work opens up a route to rationally design 2D hybrid halide perovskites for photodetectors and photovoltaic applications.