Quasi-2D perovskite architectures for next-generation solar cells: Structural engineering, charge transport, and stability enhancement

Quasi-two-dimensional (quasi-2D) perovskites have emerged as promising materials for next-generation photovoltaic technologies owing to their ability to combine high power-conversion efficiency with improved environmental stability compared with conventional three-dimensional (3D) perovskites. The incorporation of bulky organic spacer cations into layered perovskite frameworks introduces unique structural and optoelectronic characteristics that strongly influence carrier transport, defect formation, phase distribution, and operational durability. Recent advances have demonstrated that structural engineering strategies, including spacer-cation modulation, phase regulation, crystal-orientation control, additive engineering, and interface passivation, can significantly enhance photovoltaic performance while mitigating moisture-induced degradation, ion migration, and thermal instability. This review critically discusses the structural features, charge-transport mechanisms, and stability enhancement approaches in quasi-2D perovskite solar cells. Particular emphasis is placed on the relationships among layered crystal architectures, mixed-phase distributions, anisotropic carrier transport, and interfacial recombination behavior. Recent progress in device engineering, tandem photovoltaics, flexible solar cells, and scalable fabrication strategies is also summarized, together with the remaining challenges associated with phase heterogeneity, transport limitations, reproducibility, and long-term operational stability. Finally, future research directions involving multifunctional spacer molecules, advanced interface engineering, operando characterization techniques, and scalable photovoltaic integration are highlighted. This review provides a comprehensive perspective on the development of stable and high-efficiency quasi-2D perovskite solar cells for next-generation photovoltaic applications.