Unraveling the Role of MASCN in Controlling Phase Distribution for High-Efficiency Quasi-2D Stilbene-Based Perovskite Solar Cells

Abstract

The performance and stability of quasi-2D metal halide perovskite solar cells (PSCs) are strongly governed by the distribution of the low-dimensional phases. Here, we investigate the role of the methylammonium thiocyanate (MASCN) additive in quasi-2D PSCs. XRD, GIWAXS, and transient absorption spectroscopy show that SCN^– suppresses the formation of low-n phases and promotes higher-n domains. Spectroscopy and scattering measurements reveal that SCN^– coordinates Pb²⁺ to form intermediate iodoplumbate complexes that appear to assemble into large precursor aggregates, consistent with nucleation intermediates likely promoting higher-n phases. This structural reconfiguration enhances the power conversion efficiency from 5.8 to 13.4%, and retains ∼75% of their initial efficiency after 1000 h under maximum power point tracking and in N₂ atmosphere, despite the reduced fraction of the inherently stable low-n phases. These findings demonstrate that the control of the nucleation at the precursor stage is an effective strategy to tune phase distribution and improve efficiency without severely compromising stability in quasi-2D PSCs.