Ultrathin Atomic Layer Deposited TiO₂ for Surface Passivation of Hydrothermally Grown 1D TiO₂ Nanorod Arrays for Efficient Solid-State Perovskite Solar Cells

In the current work, we studied the effect of the passivation of atomic layer deposited (ALD) ultrathin TiO 2 on hydrothermally grown one-dimensional (1D) TiO 2 nanorod (NR) arrays for solid-state perovskite-sensitized solar cells. Different thicknesses of ALD-passivated TiO 2 were deposited on the hydrothermally grown 1D TiO 2 NR samples. The ALD TiO 2 thickness was varied from 1 to 5 nm by variation of the growth cycle. Our controlled results revealed that the 4 nm thin-layer-passivated TiO 2 NR sample shows a power conversion efficiency (PCE) as high as η = 12.53% (without masking) for the CH 3 NH 3 PbI 3 perovskite absorbing layer. Our results revealed that the solar cell performance with different ALD passivation thicknesses strongly affects the open-circuit voltage ( V OC ) as well as the short-circuit current density ( J SC ). However, compared with high-temperature-processed standard device configurations based on TiCl 4 -treated mesoporous TiO 2 (mp-TiO 2 ) (∼10%) and TiCl 4 -treated TiO 2 NR (∼9%) perovskite solar cells, our low-temperature-processed, pinhole-free ALD-passivated devices exhibit higher PCEs. The 4 nm passivated sample exhibits η = 12.53 ± 0.35% with J SC = 19.23 ± 0.53 mA cm –2, fill factor (FF) = 0.70 ± 0.4, and V OC = 0.931 ± 0.01 V. By control of the ultrathin passivation layer thickness, our champion cell with 4.8 nm ALD passivated TiO 2 NRs demonstrated a PCE of 13.45% with J SC = 19.78 mA cm –2, V OC = 0.945 V, and FF = 0.72. These results further emphasize hydrothermally grown 1D TiO 2 and ALD-passivated electron transporting layers (ETLs) for efficient perovskite solar cell applications.