Photoanodes with mesoporous TiO2 beads and nanoparticles for enhanced performance of CdS/CdSe quantum dot co-sensitized solar cells

Abstract

Photoanode is a critically important component in quantum dot sensitized solar cell (QDSC), and its configuration will exert a tremendous influence on the cell performance. In this paper, submicrometer-sized mesoporous TiO2 beads were prepared for QDSC application in view of their high specific surface area, superior light scattering and easy electrolyte penetration. Two configurations for the photoanodes were designed and studied with mesoporous TiO2 beads combined with nanoparticles: a double-layer configuration composed of a thick bead layer on top of a thin nanoparticle layer, and a mixture structure made of mixed mesoporous TiO2 beads and nanoparticles. Photovoltaic results showed that double-layer and mixture configurations delivered power conversion efficiencies of 4.33% and 4.65%, respectively, achieving impressive improvement compared to the single-layer films made from mesoporous beads or nanoparticles (∼4%). The mesoporous TiO2 beads served as scattering layer or scattering centers to enhance light scattering and boost the photocurrent while the incorporation of nanoparticles into the voids between mesoporous beads further increased the surface area for QD loading and led to better connection between the neighboring beads. Electrochemical impedance spectroscopy analysis revealed a retarded charge recombination for the mesoporous beads when combined with nanoparticles, reflected in the increase of open circuit voltage.