In this work, the Mg-doped ZnO (ZMO)/Lead sulfide (PbS) quantum dot (QD) heterojunction solar cells are fabricated via layer-by-layer spin-coating method. The quantum dot solar cells (QDSCs) with structure of FTO/ZMO/PbS-EMII/PbS-EDT/Au and relatively larger area of 0.372 cm(2) are prepared in ambient atmosphere. The effect of PbS active layer thickness on the photovoltaic performance of PbS QDSCs is investigated under room temperature of 293 K. It is concluded that seven spin-coating cycles of PbS active layers is the best choice for the device, and the cell with that achieves a power conversion efficiency (PCE) of 9.46%. Furthermore, the temperature dependent characteristics of PbS QDSCs are studied. It is exhibited that the power efficiency improves as the device temperature increases first then shows a decreasing trend as the temperature substantially rises. As a result, a highest PCE of 12% is shown at the working temperature of 273 K due to higher VOC and FF. Moreover, it is demonstrated the PbS QDSCs possess noticeably stability for over 30 days of storage in air.