Inverted perovskite solar cells (PSCs) are gaining significant attention for energy harvesting due to low temperature processability. However, fullerene-based eletron transport layers (ETLs) face cost and solubility challenges. Therefore, we designed a new naphthalene diimide (NDI)-based small molecule, NDINN, as a high-performance and processable ETL. Compared to perylene diimide cores, the shorter conjugation of the NDI core in NDINN reduces π-π interactions, enhancing solubility and solvent selection. Furthermore, the more electron-deficient nature of the NDI core provides a stronger driving force for self-doping, improving conductivity and mobility. These effects increased the power conversion efficiencies (PCE) of 18.36% (1 sun) and 29.55% (1000 lux LED) without additional buffer layers. NDINN also showed excellent processing versatility involving green solvents. These results suggest that NDINN can be utilized as a multifunctional ETL for high-performance PSCs.