Highly Efficient Guanidinium-Based Quasi 2D Perovskite Solar Cells via a Two-Step Post-Treatment Process

2D perovskites with alternating cations in the interlayer space (ACI) have raised increasing interest in the field of layered 2D perovskite solar cells (PVSCs). Herein, ACI quasi-2D PVSCs with a chemical formula of C(NH2)(3)(CH3NH3)(4)Pb4I13 (n = 4) are fabricated by an antisolvent method assisted by a novel two-step post-treatment process, in which guanidinium thiocyanate (GASCN) and MACl (GA = guanidinium, MA = methylammonium) are utilized as post-treatment reagents, sequentially. With the first-step post-treatment by GASCN, the grain gaps within the perovskite films are dramatically diminished, leading to increased alignment and well-ordered crystal grains. Consequently, the power conversion efficiency (PCE) of the corresponding devices increases by more than 50% (from 8.62% to 13.13%). After the second-step post-treatment by MACl, the trap states in the perovskite films are passivated, and as a result the PCE of the PVSCs is further enhanced to 15.27%. This work provides the new method of two-step post-treatment for fabrication of high quality 2D PVSC films.