Oblique Electrostatic Inkjet-Deposited TiO₂ Electron Transport Layers for Efficient Planar Perovskite Solar Cells

In this study, a new, simple, and novel oblique electrostatic inkjet (OEI) technique is developed to deposit a titanium oxide (TiO₂) compact layer (CL) on fluorine-doped tin oxide (FTO) substrate without the need for a vacuum environment for the first time. The TiO₂ is used as electron transport layers (ETL) in planar perovskite solar cells (PSCs). This bottom-up OEI technique enables the control of the surface morphology and thickness of the TiO₂ CL by simply manipulating the coating time. The OEI-fabricated TiO₂ is characterized tested and the results are compared with that of TiO₂ CLs produced by spin-coating and spray pyrolysis. The OEI-deposited TiO₂ CL exhibits satisfactory surface coverage and smooth morphology, conducive for the ETLs in PSCs. The power-conversion efficiencies of PSCs with OEI-deposited TiO₂ CL as the ETL were as high as 13.19%. Therefore, the present study provides an important advance in the effort to develop simple, low-cost, and easily scaled-up techniques. OEI may be a new candidate for depositing TiO₂ CL ETLs for highly efficient planar PSCs, thus potentially contributing to future mass production.