Low-temperature-synthesized electron transport layers (ETLs) are in demand for the industrialization and flexibility of perovskite solar cells (PeSCs). SnO(2)ETLs are prepared via chemical bath deposition at low temperature. Uniform SnO(2)ETLs with high crystallinity and transmittance are obtained from a 0.3 M SnCl(4)solution through a 100 degrees C heat treatment. They effectively transport electrons and weaken recombination loss in SnO2-based photovoltaics. SnO2-based PeSCs exhibit a power conversion efficiency (PCE) of 16.92% with a short-circuit current density (J(SC)) of 21.48 mA cm(-2)and a fill factor (FF) of 73.62%. Secondary bath modification is proposed to mend the surface pinholes of SnO(2)ETLs and boost the photoelectric properties of SnO2-based devices. The photovoltaic performance of the devices based on modified SnO2(2-SnO2) films exhibits an impressive increase compared with unembellished ones due to less pinholes and suppressed surface defects. The open circuit voltage (V-OC) and FF of 2-SnO2-based photovoltaics are enhanced to 1.10 V and 76.71%, respectively, resulting in PCE to 18.04%. Simultaneously, the dark current and hysteresis of 2-SnO2-based PeSCs are reduced because the secondary bath refines the surface nanoparticles of ETLs, passivates defects and reduces charge recombination at ETL/perovskite interfaces. Accordingly, 2-SnO2-based photovoltaics with a large area (similar to 1 cm(2)) achieves 12.91% efficiency.