Tailoring deposition conditions in spray pyrolysis for MoO₃ thin films: multi-factor effects on physical properties towards high-performance n-MoO₃ /p-Si diodes

Abstract

Molybdenum trioxide (MoO₃) thin films are wide-bandgap n-type oxides valued for their stability and high transparency in optoelectronic devices. However, optimizing spray pyrolysis deposition parameters—such as substrate temperature, solution volume, and spray rate—to achieve superior film quality and diode performance remains challenging. In this work, we systematically varied these parameters to study their effects on the structural, optical, and electrical properties of MoO₃ films and the performance of n-MoO₃/p-Si heterojunction diodes. X-ray diffraction confirmed the formation of phase-pure orthorhombic α-MoO₃ with a strong [010] orientation, and films deposited at 400 °C exhibited the best crystallinity, largest crystallite size (∼210 nm), and lowest lattice strain. Scanning electron microscopy images showed that these optimal films had smooth, dense surfaces with well-defined ∼210 nm grains. Optical measurements indicated band gaps in the range 2.81–2.98 eV, with the smallest gap (∼2.81 eV) for films deposited at 400 °C (with 15 mL solution volume and 10 mL/min spray rate). Electrical characterization of n-MoO₃/p-Si diodes revealed that devices based on the optimal films exhibited a very low reverse saturation current density (J₀ ≈ 5.4×10⁻⁵ mA/cm²) and an ideality factor of ≈5.13, corresponding to improved rectifying behavior. These enhancements are attributed to improved crystal quality, reduced defect density, and better interface formation at the MoO₃/Si junction. Our results demonstrate that precise tuning of spray pyrolysis conditions enables control over MoO₃ film microstructure and optoelectronic properties, which is crucial for optimizing MoO₃-based photodetectors, solar cells, and related devices.