Ropy Foam-Like TiO 2 Film Grown by Water-Based Process for Electron-Conduction Layer of Perovskite Solar Cells

Self-assembled TiO 2 foam-like films, were grown by the water based Streaming Process for Electrodeless Electrochemical Deposition (SPEED). The morphology of the ~1 um thick films consists of a tangled ropy structure with individual strands of ~200 nm diameter and open pores of 0.1 to 3 micron dimensions. Such films are advantageous for proposed perovskite solar cell comprising CH 3 NH 3 PbI 3 absorber with additional inorganic films as contact and conduction layers, all deposited by SPEED. Lateral film resistivity is in the range 20 – 200 kΩ-cm, increasing with growth temperature, while sheet resistance is in the range 2 – 20 × 10 8 Ω/Sq. X-ray diffraction confirms presence of TiO 2 crystals of orthorhombic class (Brookite). UV-vis spectroscopy shows high transmission below the expected 3.2 eV TiO 2 bandgap. Transmittance increases with growth temperature.