Hierarchically Nanostructured Photoelectrodes for Quantum-Dot-Sensitized Solar Cells

Abstract

Quantum-dot-sensitized solar cells (QDSSCs) recently have attracted agreat deal of attention owing to their advantages that include highmolar extinction coefficient of quantum dots, tunable energy gaps, andmultiple exciton generation. However, various architectures have not yetbeen proposed as alternative working electrodes for QDSSCs. In thisarticle, two hierarchical nanostructures will be presented asnext-generation photoelectrodes for highly-efficient QDSSCs: (a) thetertiary-hierarchically-structured mesoporous spherical (MS) TiO2 and(b) the sea urchin TiO2 (SU TiO2) particles composed of radially alignedrutile TiO2 nanowires. The MS TiO2 offers a high surface area, a highinternal reflectance in the visible region, and good pore accessibility.A conversion efficiency of 1.9 % was achieved by CdS QDSSCs made withthe MS TiO2 photoelectrode, which corresponds to similar to 58 %improvement as compared with the values obtained from the conventionaldevices made with 20-nm-sized nanocrystalline TiO2 film. Secondly, SUTiO2 was incorporated into the TiO2 nanoparticle (NP) network toconstruct the SU-NP composite film and applied to the CdS/CdSe/ZnSQDSSCs. A conversion efficiency of 4.2 % was achieved, whichcorresponds to similar to 20 % improvement as compared with the valuesobtained from the reference cell made of the NP film. We attribute thisextraordinary result to the light scattering effect and efficient chargecollection. Thus, the SU TiO2 and MS TiO2 can be promising materials forthe photoanodes of QDSSCs.