In recent years, quantum dot solar cell and perovskites solar cell have attracted much attention. In these both solar cells, in addition to absorber layer material, the electron transporting layer (ETL) material are same important. The ETL is not only crucial for achieving high PCE, but also for the device stability.Compared with other metal oxide, ZnO is particularly promising act as ETL, because of its  high transparency, suitable work function, high electron mobility. In addition, low-content doping/modification of metal oxides has been considered as a way of improving the selectivity of ETLs. In this work we are targeting in further efficiency improvement in PbS CQD solar cells and perovskites solar cells by adapting both the ZnO/PbS QD device and ZnO/MAPbI₃ /Spirodevice configuration. Due to the slightly smaller ionic radius of Mg²⁺ (57 pm) than Zn²⁺(60 pm), incorporation of Mg into ZnO layer can form ZnMgO. In such a way not only more light would pass the ZnMgO layer and transmit to the PbS QD and MAPbI₃ absorber layers contributing to larger photocurrent, but also the Fermi level in the ZnMgO layer would move up (assuming identical doping density as in ZnO) leading to improved open circuit voltage (Voc), both of which would enhance device performance. We prepared five batch devices using Zn_1−xMg_xO as theETL with x = 0, 0.05, 0.1 and 0.15. According to the XPS measurement of ZnMgO layer, all ZMO samples have Mg 2p binding energy peaks, demonstrating the successful doping of Mg elements. And the absorption measurement has showed a continuous blue shift of absorption edge with increasing Mg doping content, corresponding to broadening of the optical band gap.Benefiting from the enlarged band gap, the film transmittance increased especially in 320-400nm range, which is helpful to increase the absorption of both device absorber layer. As expected, substantial Voc and Jsc enhancements were observed for all the samples with ZnMgO as the electron transporting layer. For the PbS quantum dot solar cell, a maximum efficiency of 7.75% (0.16 cm²) has been achieved, which was 37.9% higher compared to that of the undoped devices (η=5.62%). In addition, we have successfully prepared ZnMgO/MAPbI₃-based perovskite solar cells, and a high efficiency 14 % and stable device was achieved based on the optimized 10% ZnMgO. Above resulted indicating this bandgap engineering is a very effective route for the enhancement of solar cell performance.