• • DHIII and ThPyI organic spacer cations induce spontaneous formation of stable buried 2D perovskites, resisting dissolution during subsequent 3D perovskite spin-coating and thermal annealing, ensuring structural integrity and reproducible templating.
• • The buried 2D perovskite layer acts as a crystallization template, yielding larger and more uniform 3D perovskite grains, as evidenced by SEM and GIWAXS analyses, reducing defect states and non-radiative recombination.
• • Photoluminescence spectra from both perovskite and glass sides confirm improved crystallization uniformity and defect passivation at the buried interface, directly addressing the performance-limiting factor in PSCs.
• • This approach mitigates residual strain at the buried interface, which is critical for long-term device stability, as strain-induced defects are a major degradation pathway.