Interfacial layer has a significant impact on the achievement of highly efficient organic–inorganic hybrid perovskite solar cells (PSCs). Here, we introduced a nano-ZnMgO (magnesium doped ZnO, abbreviated as ZnMgO) as interfacial layer between [6, 6]-Phenyl C 61 butyric acid methyl ester (PC 61 BM) layer and Al electrode to replace LiF or ZnO interlayer and enhance device performance. The device efficiency has been improved from 11.43% to 15.61% and the hysteresis was decreased dramatically. Such huge enhancement of power convert efficiency (PCE) can be attributed to the low dark current density, enhancement of electron-selective contact, and low energy barrier at the PC 61 BM/Al interface. We suggest that this simple nano-scale interlayer can provide an efficient charge transport and extraction for highly efficient PSCs.