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Tungsten trioxide (WO 3 ) thin films have been prepared via sol-gel spin-coating technique for different concentrations of Al (0, 3, 6, 9 and 12 wt.%) and investigated them by structural, optical, dc electrical and Al:WO 3 /p-Si heterojunction diodes. The XRD analysis reveals that the trivalent impurity of Al effectively influences the WO 3 . The UV–vis analysis shows an increase in the Al dopant that caused the band gap energy (E g ) to decrease. The SEM analysis shows that the size of the plate-like grains has reduced the Al:WO 3 thin films. The composition ratio of W, O and Al elements has been confirmed by EDX spectrum. The dc electrical conductivity analysis has identified that Mott’s 3D variable hopping (VRH) mechanism influences the Al:WO 3 thin films. The Al:WO 3 /p-Si p - n heterojunction diode parameters of ideality factor (n), barrier height (Φ B ) and series resistance (R s ) have been calculated using the J-V method. From the current density-voltage-temperature (J-V-T) analysis, the inhomogeneity of barrier heights was extracted using the thermionic emission mechanism with Gaussian distribution (GD) function. As a result, the 9 wt.% of Al:WO 3 /p-Si diode gives better results compared to the other Al:WO 3 /p-Si diodes. [ABSTRACT FROM AUTHOR]