Study On The Conductivity Mechanism And Preparation Of N/p Type Cuprous Oxide Films By Comproportionation

The cuprous oxide?Cu₂O?film is a suitable material in the application for photoelectric and photoelectrochemical conversion.The research on tunable conductivity and conductivity mechanism of Cu₂O film is important for improving photo-to-electron conversion efficiency.In this paper,The Cu₂O films were synthesized via a comproportionation in a dilute acid cupric sulfate solution?pH=5.00?.Varying concentrations of potassium nitrate?KNO₃?were added into the plating solution to modulate the conductivity type of the Cu₂O films.The modulation mechanism of conductivity type of Cu₂O films by KNO₃ were discussed in detail on the basis of research on the growth process of Cu₂O films by comproportionation.Besides,the process of comproportionation was important to study the conductivity mechanism of Cu₂O film by analyzing the growth process of Cu₂O film.The conductivity mechanism of Cu₂O film was analyzed by electrochemical impedance spectroscopy?EIS?technology and the photocurrent characterization.The main contents and results could be as follows:?1?Different conductivity type of Cu₂O films were grown on copper foils?Cu?in the cupric sulfate solution with different concentrations of KNO₃.The results showed that the Cu₂O films grown in low(?0.75 mol dm^-3)and high(?1.00 mol dm^-3)concentrations of KNO₃ presented n-type and p-type conductivity,respectively.With the increase of KNO₃concentrations,the donor carrier densities of n-type Cu₂O films gradually decreased,and the acceptor carrier densities of p-type Cu₂O films gradually increased.The mechanism of KNO₃ tunning conductivity of Cu₂O films was that nitrate?NO₃^-?ions could compete with Cu²⁺to be reduced by Cu substrate,resulting in the amount of Cu⁺decrease,and consuming hydrogen ions?H⁺?,leading to the increase of pH at the surface of Cu₂O electrode.This gave rise to the change of copper vacancy densities or oxygen vacancy densities.?2?The growth of Cu₂O films by comproportionation could be regarded as two stages.At the first stage,Cu₂O films formed by direct contact between Cu substrate and Cu²⁺??1min?.At the second stage,Cu₂O films had entirely covered Cu substrates?1 min-48 h?,at the moment,the electron provided by Cu would pass through Cu₂O film to Cu₂O/solution interface?outer interface?,Meanwhile,O^2-ions moved from outer interface to Cu/Cu₂O interface?inner interface?.Photocurrent characterization showed that the proportion between densities of intrinsic defect making Cu₂O film n-type conductivity in the outer interface and copper vacancy densities increased as the reaction time extend.EIS results indicated that the migration rate of O^2-ions from outer interface to inner interface was always greater than the supply rate of O^2-ions in the outer interface throughout the comproportionation process.Hence,oxygen vacancy densities in the outer interface gradually increasd,and copper vacancy densities in the outer interface gradually decreasd as the reaction time extend.This change law of oxygen vacancy densities was consistent with that of photocurrent results as reaction time extend.As a consequence,oxygen vacancy made Cu₂O n-type conductivity and copper vacancy made Cu₂O p-type conductivity.