Recently polyoxometalate (POM) compounds have attracted attentions in optoelectronic fields. They can be used as an interlayer between metals and semiconductors to improve the durability, stability, and efficiency of heterojunctions. The addition of polyoxometalate interlayers resulted in high external quantum efficiency and improved optoelectronic parameters, making it functional for photodiode and photodetector applications. In this study, we synthesized Keggin-type α-A-(nBu4N)3[PW9O34(tBuSiOH)3]-0.5MeCN2 polyoxometalate compound and it was characterized by SEM, FT-IR, and 31P NMR. Electrochemical behaviors of the synthesized POM compound were studied by Galvanostat. Polyoxometalate (POM) compound was deposited on n-Si by spin-coating technique. In addition, effects of POM on the electrical properties of the Al/POM/n-Si/Al device were investigated in detail. The photodiode properties were studied with (I–V) and (I-t) measurements under light intensities ranging from 20 to 100 mW/cm2. Responsivity and detectivity of the POM interlayered photodiode have been increased significantly comparing the undoped one. While Al/n-Si has shown 9.35 × 1010 Jones detectivity and 1.881 A/W responsivity at 20 mW/cm2 light power, Al/POM/n-Si photodiode device has exhibited maximum detectivity (1.29 × 1011 Jones) and responsivity (2.937A/W) at 20 mW/cm2 light power. The external quantum efficiency of polyoxometalate interlayered heterojunction varied from 17.03 % to 34.61 % under various wavelengths. The result revealed that Al/POM/n-Si device can be used for optoelectronic applications.