Octylammonium Spacer-Driven Enhanced Stability in Quasi-Two-Dimensional Perovskite Solar Cells Fabricated under Ambient Conditions

Organic–inorganic metal halide perovskites exhibit remarkable power conversion efficiency (PCE) but face challenges in stability when exposed to environmental factors such as moisture, oxygen, heat, and light. Quasi-two-dimensional (2D) perovskites fabricated by incorporating spacer cations into 3D perovskite structures offer a promising route to enhance stability without compromising optoelectronic performance. This study introduces octylammonium (OA) as a spacer cation suitable for bulk incorporation and fabrication of quasi-2D perovskites. OA improves the stability of the perovskites due to its greater chemical inertness and by defect passivation at surfaces and grain boundaries. Crystallographic, photophysical, structural, vibrational, and morphological analyses via X-ray diffraction, ultraviolet–visible spectroscopy, steady-state/time-resolved photoluminescence, Raman spectroscopy, Fourier transform infrared spectroscopy, and field-emission scanning electron microscopy reveal that OA incorporation improves crystal orientation/size and optical absorption in films, reduces defect density, improves diffusion length, and stabilizes the perovskite lattice. Quasi-2D perovskite films with proper stoichiometry (n = 80) retain their initial optoelectronic properties longer than 3D MAPbI3. Electrical characterizations, including J–V measurements, external quantum efficiency (EQE), and electrochemical impedance spectroscopy, demonstrated comparable PCE and EQE and enhanced recombination resistance in OA-incorporated devices. Demonstrating enhanced environmental stability, quasi-2D PSCs incorporating OA showed 43.6% better retention of the initial PCE than MAPbI3 during accelerated aging tests. Their superior performance was further established by a 21.6% improvement in shelf stability over 3600 h. The current work underscores the potential of spacer cation engineering in advancing stable and efficient photovoltaics. It demonstrates that stable and efficient quasi-2D perovskite solar cells can be realized under ambient fabrication conditions, without requiring any kind of controlled inert environment, through OA-mediated structural stabilization, offering a practical low-cost route toward scalable device production.