Quasi-Low-Dimensional Perovskite with Enhanced Stability Against Lattice Strain and Desired Band Edge by A-Site Design †

Abstract

Quasi-low-dimensional (QLD) additive engineering offers a compelling strategy for stabilizing layered perovskites against lattice strain (Hou et al., Science, 2025, 387, 1069) while tuning the band-edge states. Another recent experiment also demonstrated that the incorporation of charged π-stacking aromatic conjugation (CPAC) A-site cations into the prevailing bulk perovskite for solar cells can lead to reduced bandgaps owing to the strong aromatic polarity of the CPAC cations (Zhu et al., Nat. Commun., 2024, 15, 2753). In this work, by employing both QLD-additive and CPAC cation design strategies and density-functional theory computation, we examined four CPAC terminal spacers in QLD perovskites: Tropylium (Tr), Pyridinium (Py), N-Methylpyridinium (Mp), and N-Ethylpyridinium (Ep), and the hybrid frameworks of the QLD perovskite stacked with nMAPbI3 layers. Our calculation results show that Tr cation spacer, with the highest aromaticity among the four spacers, lead to the lowest conduction band minimum (CBM) once Tr-based QLD perovskite is stacked with a multilayer nMAPbI3 perovskite. Additionally, as the thickness (n) of multilayer nMAPbI3 increases, the CPAC spacers with stronger steric hindrance tend to induce phase segregation by lattice strain, leading to irregular band-gap-thickness gradients. Lattice strain resistance analysis indicates that both Tr and Py spacers, benefiting from their relatively strong hydrogen-halogen van der Waals interaction, offer relatively high tolerance to lattice deformation. These theoretical findings suggest that the integration of optimal CPAC spacers in QLD perovskites can be an effective design strategy to enhance structural stability against lattice strain while fine-tuning electronic structures for making durable optoelectronic devices.