To address the mismatch between the energy bands of the first exciton absorption peak of PbS quantum dots and the traditional electron transport layer（ETL）of ZnO—particularly when the absorption peak is red-shifted to 1 550 nm—SnO₂，with a deeper conduction band，is used as an alternative ETL. This adjustment ensures better alignment of the energy bands between the large-size PbS quantum dots and the functional layers，which helps to reduce dark current，minimize response time，and enhance device performance by improving carrier mobility at the interfaces. The PbS quantum dots，exhibiting a first exciton absorption peak at 1550 nm，are synthesized via a thermal injection method with controlled oleic acid content. SnO₂ films are then prepared using a cost-effective sol-gel process，varying precursor concentrations. Device testing reveals that with a precursor concentration of 0.15 mol/L，the dark current is approximately 10^-7 A，the photocurrent reached 10^-4 A，and the rectification ratio achieved 10³. These results demonstrate a low-cost，high-quality，and reliable method for fabricating large-size PbS quantum dot-based photovoltaic devices.