A high-performing all-transparent photodetector was created by configuring a MoO_x/NiO/ZnO/ITO structure on a glass substrate. The ITO bottom layer was applied as a back contact. To achieve the transparent p/n junction, p-type NiO was coated on the n-type ZnO layer. Reactive sputtering was used to spontaneously form the ZnO or NiO layer. In order to improve the transparent photodetector performance, the functional MoO_x window layer was used. Optically, the MoO_x window provided a refractive index layer (n=1.39) lower than that of NiO (n=2), increasing the absorption of the incident light wavelengths (λ_s). Moreover, the MoO_x window can provide a lower sheet resistance to improve the carrier collection for the photoresponses. The MoO_x/NiO/ZnO/ITO device showed significantly better photoresponses of 877.05 (at λ=460 nm), 87.30 (λ=520 nm), and 30.38 (λ=620 nm), compared to 197.28 (λ=460 nm), 51.74 (λ=520 nm) and 25.30 (λ=620 nm) of the NiO/ZnO/ITO device. We demonstrated the high-performing transparent photodetector by using the multifunctional MoO_x window layer.