Fabrication of well-aligned ZnO nanorod photoanodes for perovskite solar cells

ZnO nanorods grown on aluminum doped zinc oxide (AZO) substrate and ZnO seed layer coated substrates, including glass slides, fluorine doped tin oxide, and indium tin oxide substrates were studied. ZnO nanorods grown on AZO substrate had the best alignment and highest packing density. The growth rate of ZnO nanorods was regulated by adding polyethyleneimine (PEI) and introducing contact potential. ZnO nanorods co-adjusted by adding PEI and introducing contact-potential-driven growth formed a textured structure that led to a higher transmittance at 600–800 nm. The strong ultraviolet band emission indicated a relatively low concentration of deep level defects in ZnO nanorods. Good crystallization, together with a small amount of aluminum-doping, guaranteed high electron transfer in the ZnO nanorods. The well-aligned ZnO nanorods were incorporated into a perovskite solar cell prepared with carbon counter electrode under completely open-air conditions. A J _sc of 15.53 mA cm⁻² and an efficiency of 2.71 % were obtained for ZnO nanorods under contact-potential-driven growth. In addition, for ZnO nanorods co-adjusted by adding PEI and introducing contact potential, a J _sc of 14.87 mA cm⁻² and an efficiency of 3.62 % were obtained. However, fill factors were very low for hybrid solar cells with the structure of AZO/ZnO nanorods-CH₃NH₃PbI_xCl_3−x/carbon.