Tantalum-Doped TiO2 Prepared by Atomic Layer Deposition and Its Application in Perovskite Solar Cells.

Chia-Hsun Hsu,Shui-Yang Lien,Xiao-Ying Zhang,Ling-Yan Lin,Peng Gao,Lu-Sheng Liang,Wan-Yu Wu,Ka-Te Chen,Pao-Hsun Huang,Wen-Zhang Zhu,Yu Qiu

doi:10.3390/nano11061504

Abstract

Tantalum (Ta)-doped titanium oxide (TiO2) thin films are grown by plasma enhanced atomic layer deposition (PEALD), and used as both an electron transport layer and hole blocking compact layer of perovskite solar cells. The metal precursors of tantalum ethoxide and titanium isopropoxide are simultaneously injected into the deposition chamber. The Ta content is controlled by the temperature of the metal precursors. The experimental results show that the Ta incorporation introduces oxygen vacancies defects, accompanied by the reduced crystallinity and optical band gap. The PEALD Ta-doped films show a resistivity three orders of magnitude lower than undoped TiO2, even at a low Ta content (0.8–0.95 at.%). The ultraviolet photoelectron spectroscopy spectra reveal that Ta incorporation leads to a down shift of valance band and conduction positions, and this is helpful for the applications involving band alignment engineering. Finally, the perovskite solar cell with Ta-doped TiO2 electron transport layer demonstrates significantly improved fill factor and conversion efficiency as compared to that with the undoped TiO2 layer.

Highlights

Titanium dioxide (TiO2 ) thin films are widely studied owing to their optoelectrical properties that fulfill the requirements of numerous applications such as dye-sensitized photovoltaic devices [1], photocatalysis [2], and perovskite solar cells (PSCs) [3]
The amount of the output precursor molecules is determined by the bubbler temperature controlling the vapor pressure of the metal precursors
electron transport layer (ETL) and 0.21% for the cell with Ta-doped TiO2 ETL. This is in agreement with the findings reported by Kim et al [47], where PSCs with doped metal oxide ETLs exhibit less hysteresis compared to undoped metal oxides

Summary

Introduction

Titanium dioxide (TiO2 ) thin films are widely studied owing to their optoelectrical properties that fulfill the requirements of numerous applications such as dye-sensitized photovoltaic devices [1], photocatalysis [2], and perovskite solar cells (PSCs) [3]. In order to enhance properties, the TiO2 films are commonly doped with transition metal, rare metal, or noble metal ions [4,5,6,7,8,9]. Some studies indicate that the electron-hole recombination could be reduced due to the generation of the charge trapping centers by foreign ions [10]. Due to the wide forbidden energy gap and the absorption only at UV-light region, the TiO2 films are intentionally doped in order to reduce the energy gap and extend the light absorption to visible light in some applications [14]. The reduced band gap results from the generation of oxygen vacancies

Methods

Results

Conclusion