In this study, thin‐film microstructures of polymorphous niobium pentoxide were successfully prepared at a low temperature. Spin coating was employed to deposit the colloidal suspension before and after ultrasonic vibration. The deposited films were characterised and analysed by X‐ray diffraction, scanning electron microscopy, and spectrophotometry for optical investigation. Results show that the films prepared before ultrasonic vibration possess a smooth and uniform surface. By contrast, films that underwent further ultrasonic vibration exhibit an earth rock‐like structure and a highly oriented, void‐ and crack‐free surface. Both film structures indicate the formation of a monoclinic structure. Low energy gap values of approximately 2.5 eV and 2.25 eV are suitable for heterojunction optoelectronic applications; this condition was proven by the typical I‐V behaviours of the prepared heterojunction on the silicon substrate.