Low processing temperature of tin dioxide (SnO₂) is essential for flexible perovskite solar cells (f-PSCs). However, the low processing temperature of SnO₂ results in an inferior photovoltaic performance due to compromised carrier transport capacity in devices. The deteriorated carrier transport mainly results from the suppressed interfacial charge transfer. To overcome these issues, we used ionic liquid to modify the interface between perovskite films and SnO₂ in f-PSCs. Density Function Theory calculations were implemented to demonstrate the ionic liquid modification induced the formation of interfacial dipolar layer (IDL) and defect passivation in perovskites. The IDL and defect passivation improves the interfacial charge transfer and intra-perovskite charge transport, respectively. As a result, the f-PSCs based on ionic liquid modified SnO₂ yield the champion power conversion efficiency (PCE) of 19.0%. This work provides a method to effectively improve the performance of f-PSCs using low-temperature processed SnO₂ ESLs using affordable materials and a facile approach.