To solve the toxic issue for new-generation photovoltaic applications, tin-based perovskite solar cells are a promising alternative to their lead counterparts, but they suffer from poor stability because of their tendency to exhibit tin oxidation. Herein we report a new sequential method of deposition based on solution processing using hexafluoro-2-propanol as a solvent to deposit eight bulky ammonium cations on top of the 3D layer to form a 3D/quasi-2D layer to protect the tin perovskite grains from penetration by moisture. The formation of the 2D layer was confirmed with grazing-incidence wide-angle X-ray scattering, scanning electron microscopy, conducive atomic force microscopy, photoluminescence, and transient absorption spectroscopy measurements. The anilinium (AN) device showed a remarkable performance with an efficiency of 10.6% and with great stability in ambient air without encapsulation. The AN device also showed a self-healing effect of performance when it was subjected to a severe environment under continuous light soaking in one-sun illumination and thermal stress between 20 and 50 °C for 10 cycles.