A novel perovskite solar cell design using aligned TiO ₂ nano-bundles grown on a sputtered Ti layer and a benzothiadiazole-based, dopant-free hole-transporting material

This work highlights the utilization of a novel hole-transporting material (HTM) derived from benzothiadiazole: 4-(3,5-bis(trifluoromethyl)phenyl)-7-(5'-hexyl-[2,2'-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole (CF-BTz-ThR) and aligned TiO₂ nano-bundles (TiO₂ NBs) as the electron transporting layer (ETL) for perovskite solar cells (PSCs). The aligned TiO₂ NBs were grown on titanium (Ti)-coated FTO substrates using a facile hydrothermal method. The newly designed CF-BTz-ThR molecule with suitable highest occupied molecular orbital (HOMO) favored the effective hole injection from perovskite deposited aligned TiO₂ NBs thin film. The PSCs demonstrated a power conversion efficiency (PCE) of ∼15.4% with a short circuit current density (J_sc) of ∼22.42 mA cm^-2 and an open circuit voltage (V_oc) of ∼1.02 V. The efficiency data show the importance of proper molecular engineering whilst highlighting the advantages of dopant-free HTMs in PSCs.