The outstanding advantages of lightweight and flexibility enable flexible perovskite solar cells (PSCs) to have great application potential in mobile energy devices. Due to the low cost, low-temperature processibility, and high electron mobility, SnO₂ nanocrystals have been widely employed as the electron transport layer in flexible PSCs. To prepare high-quality SnO₂ layers, a monodispersed nanocrystal solution is normally used. However, the SnO₂ nanocrystals can easily aggregate, especially after long periods of storage. Herein, we develop a green and cost-effective strategy for the synthesis of high-quality SnO₂ nanocrystals at low temperatures by introducing small molecules of glycerol, obtaining a stable and well-dispersed SnO₂-nanocrystal isopropanol dispersion successfully. Due to the enhanced dispersity and super wettability of this alcohol-based SnO₂-nanocrystal solution, large-area smooth and dense SnO₂ films are easily deposited on the plastic conductive substrate. Furthermore, this contributes to effective charge transfer and suppressed non-radiative recombination at the interface between the SnO₂ and perovskite layers. As a result, a greatly enhanced power conversion efficiency (PCE) of 21.8% from 19.2% is achieved for small-area flexible PSCs. A large-area 5 cm × 5 cm flexible perovskite solar mini-module with a champion PCE of 16.5% and good stability is also demonstrated via this glycerol-modified SnO₂-nanocrystal isopropanol dispersion approach.