Here, for the first time, MWCNT/Zinc acetate (MWCNT
ZnAc2) was synthesized from Amaranthus spinosus and used as a novel additive for carbon-based perovskite solar cells. A high-quality perovskite layer with larger grain size, lower defect density, larger grain size, and purer perovskite composition was obtained by adding a very small amount of MWCNT/ZnAc2 nanocomposite through a straightforward one-step spin coating method.