Improvement of inverted type organic solar cells performance by incorporating Mg dopant into hydrothermally grown ZnO nanorod arrays

•Mg-doped ZnO nanorod arrays were synthesized by hydrothermal method.•Growth of ZnO nanorods was strongly correlated to Mg concentration.•The PCE of device with optimum Mg concentration increased by 225%.•The mechanism of PCE improvement by Mg doping was revealed. The Mg concentration dependence of the performance of inverted type organic solar cells based on Mg-doped ZnO nanorod arrays and poly(3-hexylthiophene) (P3HT) has been investigated. The Mg dopants with various concentrations (0, 1, 3 and 5at.%) were introduced during the hydrothermal growth of the ZnO nanorod arrays on fluorine-doped tin oxide (FTO) glass substrate. The P3HT was deposited onto Mg-doped ZnO nanorod arrays by spin coating technique, followed by deposition of Ag as anode using magnetron sputtering technique. The length and density of Mg-doped ZnO nanorods increased, whereas the diameter decreased with the Mg concentration. The short circuit current density (Jsc) and open circuit voltage (Voc) improved with increasing of Mg concentration up to 3at.%, which could be attributed to increased interfacial area for more efficient exciton dissociation and reduced charge recombination as a result of lower number of oxygen interstitials which act as electron traps in ZnO. However, the Jsc and Voc started to decrease at Mg concentration of 5at.%, mainly due to poor infiltration of P3HT into the high-density 5at.% Mg-doped ZnO nanorod arrays and increase of Mg dopant-related trapping centers. The highest power conversion efficiency of 0.36±0.02% was achieved at Mg doping concentration of 3at.%, an enhancement of 225% as compared to that based on undoped ZnO nanorod arrays.