Depleted bulk heterojunction (DBH) PbS quantum dot solar cells (QDSCs), appearing with boosted short-circuit current density (Jsc), represent the great potential of solar radiation utilization, but suffer from the problem of increased interfacial charge recombination and reduced open-circuit voltage (Voc). Herein, we report that an insertion of ultrathin Al2O3 layer (ca. 1.2 ? thickness) at the interface of ZnO nanowires (NWs) and PbS quantum dots (QDs) could remarkably improve the performance of DBH-QDSCs fabricated from them, i.e., an increase of Voc from 449 mV to 572 mV, Jsc from 21.90 mA/cm2 to 23.98 mA/cm2, and power conversion efficiency (PCE) from 4.29％to 6.11％. Such an improvement of device performance is ascribed to the significant reduction of the interfacial charge recombination rate, as evidenced by the light intensity dependence on Jsc and Voc, the prolonged electron lifetime, the lowered trap density, and the enlarged recombination activation energy. The present research therefore provides an effective interfacial engineering means to improving the overall performance of DBH-QDSCs, which might also be effective to other types of optoelectronic devices with large interface area.