Conformal atomic layer deposition (ALD) technique is employed to make semi-transparent TaOxNy, providing the possibility to build semi-transparent oxy(nitride) heterojunction photoanodes on conductive substrates. A generalized approach was developed to manufacture semi-transparent quaternary metal oxynitrides on conductive substrates beyond semi-transparent binary Ta3N5 photoanodes aiming for wireless tandem photoelectrochemical (PEC) cells.