Effect of Annealing Temperature on Spatial Atomic Layer Deposited Titanium Oxide and Its Application in Perovskite Solar Cells

Abstract

<jats:p>In this study, spatial atomic layer deposition (sALD) is employed to prepare titanium dioxide (TiO2) thin films by using titanium tetraisopropoxide and water as metal and water precursors, respectively. The post-annealing temperature is varied to investigate its effect on the properties of the TiO2 films. The experimental results show that the sALD TiO2 has a similar deposition rate per cycle to other ALD processes using oxygen plasma or ozone oxidant, implying that the growth is limited by titanium tetraisopropoxide steric hindrance. The structure of the as-deposited sALD TiO2 films is amorphous and changes to polycrystalline anatase at the annealing temperature of 450 °C. All the sALD TiO2 films have a low absorption coefficient at the level of 10−3 cm−1 at wavelengths greater than 500 nm. The annealing temperatures of 550 °C are expected to have a high compactness, evaluated by the refractive index and x-ray photoelectron spectrometer measurements. Finally, the 550 °C-annealed sALD TiO2 film with a thickness of ~8 nm is applied to perovskite solar cells as a compact electron transport layer. The significantly enhanced open-circuit voltage and conversion efficiency demonstrate the great potential of the sALD TiO2 compact layer in perovskite solar cell applications.</jats:p>

Influence of Alumina Addition on the Optical Properties and the Thermal Stability of Titania Thin Films and Inverse Opals Produced by Atomic Layer Deposition

“…Upon heat treatment, all ternary compositions as well as the pure TiO 2 thin film showed an increase in the refractive index, which can be related to two factors: on the one hand, heat treatments can promote the removal of common film impurities, such as nitrogen, carbon, as well as hydrogen and could lead to further densification of the thin film. Such a process could explain the slight increase in the refractive index observed at lower temperatures [ 53 , 54 ]. On the other hand, the annealing of ALD films led to crystallization of phases within the film, discussed in detail in the XRD section, which have higher refractive indexes than the as-deposited amorphous thin films [ 26 ].…”

“…However, amorphous films present a lower refractive index than their crystalline counterparts [ 25 , 26 , 27 , 30 ] and are therefore less sought for application as photonic crystal-based reflectors, but they are interesting for applications such as antibacterial films or oxygen sensors [ 56 ]. Moreover, the compositions with less than 14% of alumina, including the pure titania one, could be attractive for photocatalysis applications, as the anatase phase often exhibits higher photocatalytic activity than the rutile phase [ 54 , 55 ].…”

Inorganic Materials by Atomic Layer Deposition for Perovskite Solar Cells

“…Some common examples are pulsed-CVD [ 60 ], AP-CVD [ 64 ], and s-ALD [ 45 , 79 ]. Pulsed-CVD involves reducing the carrier purging step during the ALD sequence and pulsing the ALD precursors simultaneously, instead of separately, to reduce the deposition time [ 80 ].…”

The Effects of Annealing Temperatures and Dimethylformamide Doses on Porous TiO2 Films

“…Furthermore, TiO 2 is commonly used as a substitute for storing gas in silicon dioxide [1,2] and as a replacement for ultra-thin oxide dielectric in logic elements [3][4][5] due to its high dielectric constant. Additionally, TiO 2 is also used in a variety of emerging electronics, including solar cells [6][7][8][9][10][11], perovskite-based solar cells [12,13], anti-reflection coatings [7,8], gas sensors [14,15], electrochromic displays [16,17], planar waveguides [4], and field-effect transistors [3,5]. In 1972, multiphase photocatalysts were proposed by two researchers, Fujishima and Honda, via decomposing water on TiO 2 to generate oxygen and hydrogen gas [18].…”