Influence of Rutile-TiO2 nanorod arrays on Pb-free (CH3NH3)3Bi2I9-based hybrid perovskite solar cells fabricated through two-step sequential solution process

Highlights: • The rutile-TiO₂ NRAs as ETL to fabricate MBI PSCs were taken in detail. • Two-step sequential solution process was introduced firstly to fabricate MBI. • All the devices were fabricated in ambient air. • The impact of rutile-TiO₂ ETL thicknesses on the τ_ave and PCE were explored. • The device exhibited excellent long-term stability. The organic–inorganic perovskite compound (CH₃NH₃)₃Bi₂I₉ (MBI) has lower toxicity and higher stability than lead-based perovskite. In this work, we fabricated MBI perovskite-based solar cells (PSCs) through a two-step sequential-solution process by using rutile TiO₂ nanorod array (NRA) films as the electron transporting layer (ETL) for the first time. The thickness, roughness, and crystal structure of the rutile TiO₂ NRAs prepared by hydrothermal method with different reaction times were thoroughly characterized and correlated with the photovoltaic performance of PSCs. Results of morphological and structural analyses, as well as time-resolved photoluminescence studies, indicated the effect of TiO₂ NRA film thickness on the carrier recombination and photovoltaic performance of MBI-based PSCs. The MBI-based device was also stable in an environment with >50% humidity for more than 67 days.