Unraveling the Role of Chloride in Vertical Growth of Low-Dimensional Ruddlesden-Popper Perovskites for Efficient Perovskite Solar Cells

Recently, low-dimensional Ruddlesden-Popper (LDRP) perovskite-based solar cells (PSCs) have been extensively studied because of their robust stability. However, because of the poor conductivity of the organic spacer, the charge transport across the spacers in the LDRP perovskite is considerably poor, and thus regulation of the growth orientation of LDRP cells is of primary importance. So far, the key role of organic cations in controlling the growth orientation of LDRP films has been widely studied, but the impact of halogens has not been sufficiently investigated. Herein, we demonstrate the important role of halogens in determining the characteristics of benzylamine (BZA)-based LDRP perovskite films, where different BZAX salts (X = Cl, Br, I) are adopted. Compared to Br and I, Cl is shown to prominently enlarge the grain size, promote the vertical orientation, reduce the trap state density, and prolong the carrier lifetime of LDRP film, and all these merits effectively accelerate the carrier transport within the film. As a result, a PSC device based on BZACl delivers a champion PCE of 17.25% with much improved device stability. This work unravels the vital role of Cl in regulating the crystallization process of LDRP films, which provides a facile approach for boosting the performance of LDRP-based PSCs.