Publication date: 21st July 2025
Perovskite solar cells (PSCs) offer high power conversion efficiency and low production costs [1], but their commercial potential is still constrained by insufficient long-term stability. The incorporation of two-dimensional (2D) cationic layers onto three-dimensional (3D) perovskite frameworks has emerged as a promising strategy to mitigate instability in perovskite solar cells (PSCs) [2]. While this approach enhances moisture resistance and suppresses interfacial recombination, the relationship between spacer chemistry, concentration, and phase behavior remains not fully understood [3]. In this work, we present a systematic comparison of two alkylammonium spacers—butylammonium iodide (BAI) and butyl-1,4-diammonium diiodide (BDAI₂)—which form Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) 2D phases, respectively, onto CH₃NH₃PbI₃ 3D perovskite.
By varying spacer concentration under ambient conditions, we accessed distinct structural regimes. At high concentrations ([BAI] = 50 mmol L⁻¹ and [BDAI₂] = 5 mmol L⁻¹), it is observed that BAI facilitated the evolution from n = 1 to n = 2 RP phases, suggesting dynamic structural reorganization, while using BDAI2 DJ structures showed rapid degradation without observable phase progression. At lower concentrations, both spacers acted primarily as passivation agents, but only BAI significantly enhanced environmental stability without disrupting charge transport.
Characterizations via UV–vis, XRD, SEM, c-AFM, PL, and EIS demonstrated a strong correlation between dimensionality, interfacial conductivity, and long-term device performance. Notably, DJ-phase samples exhibited promising initial optoelectronic properties but suffered from severe degradation due to humidity.
Our findings highlight critical trade-offs between rigidity and ionic migration in hybrid perovskite systems. This study offers insights into interface engineering and dimensional control, paving the way for the design of robust, high-efficiency perovskite solar cells (PSCs) with improved operational lifetimes.
The authors acknowledge FAPESP (Grants 2023/05797-6, 2022/07268-8, 2023/09820-2, 2017/11986-5) and CNPq (Grants 406470/2022-7, 305631/2022-5) for financial support.
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