Methylammonium chloride or guanidinium chloride as an additive to improve performance of 2D alternating cation perovskite solar cells: A direct comparison

Quasi two-dimensional (2D) (C(NH2)3)(CH3NH3)nPbnI3n+1 (nominally, n = 4) perovskite solar cell with alternating cations in the interlayer space (ACI) is fabricated using methylammonium chloride (MACl) or guanidinium chloride (GACl) as an additive in precursor solution. With an appropriate molar ratio of MACl or GACl, the 2D perovskite films show better crystallinity, smaller defect density and higher carrier mobility, resulting in more than 30 % enhancement of power conversion efficiency (PCE) compared to that of without additives. Particularly, an optimal concentration of GACl eventually leads to the best PCE of 14.3 % here, and importantly, eliminating current density-voltage (J-V) curves hysteresis which is prominent in devices from precursor solutions with various concentration of MACl. Thus, GACl is demonstrated firstly as a better additive compared to commonly used MACl in synthesizing ACI perovskite, providing a possible constructive route to fabricate highly efficient and J-V hysteresis-free solar cells.