Ropy foam-like TiO2 film grown by water-based process for electron-conduction layer of perovskite solar cells

Abstract

Self-assembled TiO2 foam-like films, were grown by the water based Streaming Process for Electrodeless Electrochemical Deposition (SPEED). The morphology of the ∼1 µm 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 CH3NH3PbI3 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 x 108 Ω/Sq. X-ray diffraction confirms presence of TiO2 crystals of orthorhombic class (Brookite). UV-vis spectroscopy shows high transmission below the expected 3.2 eV TiO2 bandgap. Transmittance increases with growth temperature.

Smooth TiO2 Thin Films Grown by Aqueous Spray Deposition for Long-Wave Infrared Applications

“…The complex refractive index spectra have been reported out to far infrared wavelengths (125 µm) for TiO 2 thin films prepared by vacuum-based physical deposition [2,3]. Our atmospheric-pressure aqueous inhomogeneous-chemical-reaction method has unique potential for low cost, large area, perfectly conformal [1,4] roll-to-roll manufacturing. Physical and optical properties of such films are reported here with particular emphasis on application to infrared photonics, such as metal-insulator-metal plasmonic resonant absorbers [5] and planer waveguides [6].…”

“…Titanium dioxide is a very well-studied material with wide ranging applications, as discussed in [1]. TiO 2 films have been deposited by a wide variety of methods, representatively summarized in [1].…”

“…Titanium dioxide is a very well-studied material with wide ranging applications, as discussed in [1]. TiO 2 films have been deposited by a wide variety of methods, representatively summarized in [1]. This paper considers TiO 2 as a potentially useful material for long-wave infrared applications motivated by the relatively low dispersion for TiO 2 in the 8 to 12 µm wavelength range, in comparison to commonlyused SiO 2 .…”

“…This work presents a potentially advantageous aqueous deposition method that provides smooth conformal coatings. We designate the film considered here as "smooth SPEED" TiO 2 to distinguish it from a highly structured film grown by a different SPEED recipe reported earlier [1], which was designated "Ropy SPEED" according to its observed morphology.…”