Pure carbon nanotubes (CNTs) and their derivatives grafted with the regiorandom poly(3-dodecyl thiophene) (CNT-g-PDDT) and regioregular poly(3-hexylthiophene) (CNT-g-P3HT) polymers were employed to improve the morphological, optical, and photovoltaic properties of CH₃NH₃PbI₃ perovskite solar cells. Although the grafted CNT components improved the cell characteristics, bare CNTs destroyed them. The regioregularity and graft length influences were investigated on the system behavior. The CNT nanostructures grafted with the shorter P3HT backbones demonstrated the best results, i.e., 79.9 Ω, 23.60 mA cm⁻², 76%, 0.97 V and 17.40%. This originated from the higher crystalline peak intensities for both P3HT (5.6–5.8°) and CH₃NH₃PbI₃ (14.81, 20.91, 24.11, 29.21 and 32.51°) precursors and also the larger grain sizes (5 (600 nm) versus 50 (490 nm) kDa). The perovskite + CNT-g-P3HT devices, in particular the CNTs with shorter grafts, possessed faster electron transport and lower carrier recombination compared with the other solar cells, as evidenced by the larger short-circuit current density.