Sustainable energy generation has been a growing concern worldwide due to the alarming effects of climate changes in the last few decades. In this scenario, perovskite solar cells hold great promise in contributing for a greener global energy matrix. Despite the great potential of this technology, several difficulties to deploy perovskite solar panels are yet to be overcome, being their long-term stability one of the most critical. In this sense, this work offers an alternative to improve the long-term, operational stability of the devices by passivating the CsFAMA perovskite active layer with a mixture of N-(2-aminoethyl)naphthalimide and mercaptopropionic acid. These modifications improved the perovskite and device stability under ambient conditions. The solar cells without encapsulation and with post-treatment with 5 mM modifier solution retained ca. 90% of its initial power conversion efficiency (PCE) after 500 h exposed to ambient conditions, while standard solar cells retained ca. 58%. Our approach offers a simple new method to improve the stability of perovskite solar cells using an unexplored combination of passivating molecules.