This study investigates the electronic structure and photo/electrochemical properties of high-quality dense ZnO thin films prepared by spray pyrolysis (SP) and pulsed reactive magnetron sputtering combined with radio frequency electron cyclotron wave resonance plasma (MS). The films were characterized using AFM, XRD, Kelvin probe, cyclic voltammetry, electrochemical impedance spectroscopy, and UV photoelectrochemistry. The results show that the films have a high-quality compact morphology with crystallite sizes ranging from 12 to 26 nm, indicating they consist of approximately 2–10 monolayers of single crystallites. The films exhibit nearly ideal rectifying behavior on an electrochemical interface, with SP films being more anisotropic than MS films. The work function of the ZnO/electrolyte interface (φfb) is approximately 4.3 eV for SP films and 4.4 eV for MS films. Annealing has a minimal effect on the work function. Donor concentrations are significantly lower for MS films compared to SP films, attributed to the quenching of oxygen vacancies in the ECWR plasma. The work function of the ZnO/air interface (φK) is approximately 4.2 eV for all films, but systematically larger for annealed films. UV excitation significantly enhances the work function, which persists after UV illumination is turned off. Photoelectrochemical water oxidation demonstrates unusually large photocurrents on both MS- and SP-virgin films. The subsequent fading of photocurrents is discussed in terms of photocorrosion and work function changes due to oxygen vacancies. The study highlights the importance of understanding the electronic structure of ZnO thin films, particularly near the conduction band minimum, for their application in photoelectrochemical and photovoltaic devices. The results suggest that ZnO thin films prepared by these methods are promising materials for such applications.This study investigates the electronic structure and photo/electrochemical properties of high-quality dense ZnO thin films prepared by spray pyrolysis (SP) and pulsed reactive magnetron sputtering combined with radio frequency electron cyclotron wave resonance plasma (MS). The films were characterized using AFM, XRD, Kelvin probe, cyclic voltammetry, electrochemical impedance spectroscopy, and UV photoelectrochemistry. The results show that the films have a high-quality compact morphology with crystallite sizes ranging from 12 to 26 nm, indicating they consist of approximately 2–10 monolayers of single crystallites. The films exhibit nearly ideal rectifying behavior on an electrochemical interface, with SP films being more anisotropic than MS films. The work function of the ZnO/electrolyte interface (φfb) is approximately 4.3 eV for SP films and 4.4 eV for MS films. Annealing has a minimal effect on the work function. Donor concentrations are significantly lower for MS films compared to SP films, attributed to the quenching of oxygen vacancies in the ECWR plasma. The work function of the ZnO/air interface (φK) is approximately 4.2 eV for all films, but systematically larger for annealed films. UV excitation significantly enhances the work function, which persists after UV illumination is turned off. Photoelectrochemical water oxidation demonstrates unusually large photocurrents on both MS- and SP-virgin films. The subsequent fading of photocurrents is discussed in terms of photocorrosion and work function changes due to oxygen vacancies. The study highlights the importance of understanding the electronic structure of ZnO thin films, particularly near the conduction band minimum, for their application in photoelectrochemical and photovoltaic devices. The results suggest that ZnO thin films prepared by these methods are promising materials for such applications.