This study investigates the effectiveness of oleic acid-functionalized Al₂O₃ nanoparticle thin-film coatings in reducing dust-induced performance losses in photovoltaic (PV) systems. Coating performance was evaluated using spraying durations of 20, 40, and 80 s and oleic acid concentrations between 0.5% and 4.5%. Characterization results indicated that the optimal coating was obtained using a 40-second spraying time and a 1.5% oleic acid concentration, resulting in a 231 nm film thickness and a water contact angle of 75.47°, confirming improved surface properties. Laboratory experiments showed that the coated surfaces accumulated, on average, 6.9 mg/cm² less dust than uncoated ones, preventing 0.6–3.0% efficiency loss. A central composite design (CCD) approach was applied by considering temperature, relative humidity, wind speed, and initial dust load as environmental variables. Field tests performed under real outdoor conditions demonstrated that coated Mini-PV modules produced 0.5–0.8 W more daily energy compared to uncoated panels. However, environmental factors such as temperatures above 35 °C and the presence of hydrophobic pollutants reduced long-term coating effectiveness. Overall, the findings indicate that oleic acid-modified Al₂O₃ coatings may serve as a passive strategy for mitigating dust accumulation and enhancing PV panel performance under certain conditions.