Optimising ZnO seed layer to improve the growth of the dense, aligned ZnO nanorods as an electron transport layer in perovskite solar cell applications

Vertically aligned ZnO nanorods were grown using the chemical deposition method. The presence of various ZnO seed layers in the growth process was examined. Perovskite cells, with these films, were also studied. XRD pattern confirmed the deposition of nanorods with hexagonal phasing in the (001) direction for all seeds, though with different intensities. Consistent with the FESEM images, peak intensity was directly related to the improvement in the alignment and density of the nanorods. Film transparency was also directly associated with the alignment of the ZnO structure. The optical bandgap of the nanorods was close to 3.2 eV for different seed layers. Open circuit voltage and fill factor of the cells were both found to increase from 0.55 V to 0.66 V and 0.44 to 0.49, respectively, through improving the density and alignment of the nanorods. The highest efficiency for the fabricated cells was 4.56%.