Engineering Processes at the Interface of p-Semiconductor for Enhancing the Open Circuit Voltage in p-Type Dye-Sensitized Solar Cells

To prevent the interfacial charge recombination between injected holes in the valence band and the redox mediator in the electrolyte in p-type dye sensitized solar cells (p-DSSC) the passivation of the recombination sites by organic insulator chenodeoxycholic acid (CDCA) layer is critically investigated in this study. Rather than classical coating of the semiconductor's surface by simultaneous co-adsorption of CDCA during the dyeing step, two other methods are investigated. The first consists in dissolving CDCA in the electrolyte, while the second consists in spin coating an ethanol solution of CDCA onto the already dyed photocathode. In this study, different sensitizers, electrolytes, and p-SCs, (NiO, CuGaO2) are explored. Analysis of the current/voltage curves and electrochemical impedance spectroscopy provides evidence that the role of the CDCA layer is to create a physical barrier to prevent the approach of the redox mediator from the NiO surface and consequently raise the open circuit voltage (Voc). The important finding of this study is the demonstration that the Voc in p-DSSC is heavily limited by interfacial charge recombination and that higher Voc values much above 100 mV and as high as 500 mV can be attained with conventional materials (NiO) if this deleterious side reaction can be suppressed or diminished.