Kinetics of photocurrent generation and an efficient charge separation of a dye-sensitized n-Cu_2O/p-CuSCN junction photoelectrode in a solid-state photovoltaic cell

摘要

A Cu-Cu_2O/dye/p-CuSCN junction photoelectrode is fabricated to produce a solid-state dye-sensitized photovoltaic cell. Samples are characterized by XRD, SEM and surface resistivity measurements. Photocurrent generation is found due to light absorption of n-Cu_2O thin film and dye sensitization between p-CuSCN and the dye. Kinetics of the photocurrent generation of the dye sensitization is studied solving the rate equations by the iteration method obtaining a relationship for the photocurrent quantum efficiency (Φ) depending on the surface concentration (D_o) of the dye and the rate constants of the reactions with connection to the dye sensitization process. The solution obtained in the steady state by iteration is found to be of the form Φ = AD_o—BD_o~2 (A and B are constants related to the reaction rates of the photocurrent generation process and the concentration of the n-Cu_2O film). The variation of the n-Cu_2O concentration with photocurrent is presented. A photocurrent enhancement is observed for the Cu-Cu_2O/dye/p-CuSCN photovoltaic cell compared to that of Cu-Cu_2O, Cu/p-CuSCN/dye and Cu-Cu_2O/p-CuSCN photovoltaic cells. Good rectification characteristics are observed for the Cu-Cu_2O/p-CuSCN photoelectrode compared to that of Cu-Cu_2O and Cu/p-CuSCN photoelectrodes. Photocurrent enhancement is found due to the efficient charge separation process at the n-p junction. Energy band structures of the n-p junction are proposed according to the onset potentials which are used to discuss the mechanism of the efficient charge separation suppressing the recombination process.