Optimization of Cr-doped ZnO Thin Films Deposited by Chemical Spray Pyrolysis for Enhanced Structural, Photoluminescence, and Morphological Performance

Cr-doped ZnO (CrZnO) thin films were deposited on glass substrates using chemical spray pyrolysis (CSP). The study systematically investigates the influence of Cr concentration (0–2 at%), substrate temperature (300–450 °C), and spray parameters on structural, morphological, and photoluminescence (PL) properties. X-ray diffraction (XRD) analysis reveals that all films crystallize in the wurtzite ZnO structure with preferential orientation; low-level Cr incorporation leads to a modest decrease in crystallite size and a small lattice distortion, while higher doping (≥3 at%) introduces secondary-phase features and increased defect density. Scanning electron microscopy (SEM) show grain refinement and reduced surface roughness at optimized doping and deposition conditions. Room-temperature PL spectra show a strong near-band-edge (NBE) UV emission and a reduced visible deep-level emission (DLE) for films optimized at 1–2 at% Cr, indicating lower nonradiative recombination and fewer oxygen-vacancy-related defects. The optimized CrZnO films (2 at% Cr, substrate temperature 375 °C, precursor concentration 0.1 M, spray rate 2 mL min−1) demonstrated the best combined structural order, strong NBE PL, and smooth morphology, making them promising for optoelectronic and sensing applications.