Tin oxide (SnO2) has been extensive researched as an electron-transport layer (ETL) in inverted organic light emitting devices (OLEDs) because of its outstanding advantages in many aspects. However, there are defect sites for nonradiative recombination, which have limited its widespread application as ETLs in the SnO2 -based OLEDs. Herein, a novel approach utilizing Polyethyleneimine (PEI) for modifying SnO2 is introduced. OLEDs were fabricated with the structure of ITO/ SnO2/ PEI/ PVK: Alq3/ NPB/ MoO3/ Al. The atomic force microscopy (AFM), photoluminescence (PL), Time-Resolved Fluorescence Transient Lifetime (TRPL) and current density-voltage-luminescence of the OLEDs were characterized, then the dependence of SnO2 and PEI thickness on device characteristics was investigated. It revealed that this modification serves dual purposes of roughness reduction and surface-defect passivation, can inhibit the leakage current of OLEDs and avoid the quenching of excitons. OLEDs with PEI-modified SnO2 (SnO2/PEI) ETL exhibit a remarkable current efficiency (CE) of 3.15 cd/A, which significantly exceeds that (0.85 cd/A) achieved with bare SnO2-based OLEDs, along with effectually reducing the turn-on voltage from 4.5 to 3.5 V. This study confirms the efficacy of PEI for efficient OLEDs, paving the way for SnO2 applications.