Impact of Film Thickness of Ultrathin Dip-Coated Compact TiO2 Layers on the Performance of Mesoscopic Perovskite Solar Cells

A1 Journal article (refereed)


Internal Authors/Editors


Publication Details

List of Authors: Muhammad T. Masood, Christian Weinberger, Jawad Sarfraz, Emil Rosqvist, Simon Sandén, Oskar J. Sandberg, Paola Vivo, Gufran Hashmi, Peter D. Lund, Ronald Österbacka, Jan-Henrik Smått
Publisher: American Chemical Society
Publication year: 2017
Journal: ACS Applied Materials and Interfaces
Volume number: 9
Issue number: 21
Start page: 17906
End page: 17913
eISSN: 1944-8252


Abstract

Uniform and pinhole-free electron-selective TiO2 layers are
of utmost importance for efficient perovskite solar cells. Here we used a
scalable and low-cost dip-coating method to prepare uniform and
ultrathin (5–50 nm) compact TiO2 films on fluorine-doped tin oxide (FTO) glass substrates. The thickness of the film was tuned by changing the TiCl4 precursor concentration. The formed TiO2 follows the texture of the underlying FTO substrates, but at higher TiCl4
concentrations, the surface roughness is substantially decreased. This
change occurs at a film thickness close to 20–30 nm. A similar TiCl4 concentration is needed to produce crystalline TiO2 films. Furthermore, below this film thickness, the underlying FTO might be exposed resulting in pinholes in the compact TiO2 layer. When integrated into mesoscopic perovskite solar cells there appears to be a similar critical compact TiO2
layer thickness above which the devices perform more optimally. The
power conversion efficiency was improved by more than 50% (from 5.5% to
∼8.6%) when inserting a compact TiO2 layer. Devices without or with very thin compact TiO2 layers display JV
curves with an “s-shaped” feature in the negative voltage range, which
could be attributed to immobilized negative ions at the
electron-extracting interface. A strong correlation between the
magnitude of the s-shaped feature and the exposed FTO seen in the X-ray
photoelectron spectroscopy measurements indicates that the s-shape is
related to pinholes in the compact TiO2 layer when it is too thin.


Keywords

compact TiO2, dip coating, perovskite solar cells, pinhole free, TiCl4

Last updated on 2019-21-09 at 03:56