TUTCRIS

TY - JOUR

T1 - Impact of film thickness of ultra-thin dip-coated compact TiO2 layers on the performance of mesoscopic perovskite solar cells

AU - Masood, Muhammad Talha

AU - Weinberger, Christian

AU - Sarfraz, Jawad

AU - Rosqvist, Emil

AU - Sandén, Simon

AU - Sandberg, Oskar

AU - Vivo, Paola

AU - Hashmi, Ghufran

AU - Lund, Peter D.

AU - Österbacka, Ronald

AU - Smått, Jan-Henrik

PY - 2017/5/31

Y1 - 2017/5/31

N2 - 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 ultra-thin (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 J-V 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-shape 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.

AB - 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 ultra-thin (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 J-V 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-shape 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.

U2 - 10.1021/acsami.7b02868

DO - 10.1021/acsami.7b02868

M3 - Article

VL - 9

SP - 17906

EP - 17913

JO - ACS Applied Materials & Interfaces

JF - ACS Applied Materials & Interfaces

SN - 1944-8244

IS - 21

ER -