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

Abstract

In the current work, we studied the effect of the passivation of atomic layer deposited (ALD) ultrathin TiO2 on hydrothermally grown one-dimensional (1D) TiO2 nanorod (NR) arrays for solid-state perovskite-sensitized solar cells. Different thicknesses of ALD-passivated TiO2 were deposited on the hydrothermally grown 1D TiO2 NR samples. The ALD TiO2 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 TiO2 NR sample shows a power conversion efficiency (PCE) as high as η = 12.53% (without masking) for the CH3NH3PbI3 perovskite absorbing layer. Our results revealed that the solar cell performance with different ALD passivation thicknesses strongly affects the open-circuit voltage (VOC) as well as the short-circuit current density (JSC). However, compared with high-temperature-processed standard device configurations based on TiCl4-treated mesoporous TiO2 (mp-TiO2) (∼10%) and TiCl4-treated TiO2 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 JSC = 19.23 ± 0.53 mA cm–2, fill factor (FF) = 0.70 ± 0.4, and VOC = 0.931 ± 0.01 V. By control of the ultrathin passivation layer thickness, our champion cell with 4.8 nm ALD passivated TiO2 NRs demonstrated a PCE of 13.45% with JSC = 19.78 mA cm–2, VOC = 0.945 V, and FF = 0.72. These results further emphasize hydrothermally grown 1D TiO2 and ALD-passivated electron transporting layers (ETLs) for efficient perovskite solar cell applications.