Hierarchical zinc oxide pomegranate and hollow sphere structures as efficient photoanodes for dye-sensitized solar cells

The hierarchically structured ZnO pomegranates as well as hollow spheres have been prepared in a solvothermal assisted process using ethylene glycol as a solvent and l -ascorbic acid and oxalic acid as additives/surfactants respectively, without using water as solvent. Depending on the surfactant used, the morphology of the ZnO hierarchical nanostructures has changed dramatically which can be attributed to the reaction kinetics affected by presence of generated solvents, evolved gases. The structural analysis reveals the formation of wurtzite hexagonal crystalline structure. Electron microscopy images show the pomegranate and hollow sphere like morphology. The secondary nanoscale growth has been observed on the shell of pomegranate like ZnO microspheres. The synthesized ZnO hierarchial nanostructures have been used as photoanode in dye sensitized solar cells (DSSCs) which showed enhanced light harvesting properties than the commercial ZnO. Pomegranate like structure has displayed better light conversion efficiency (4.35%) as compared to ZnO hollow sphere structures (3.28%). This enhancement in photocurrent and power conversion efficiency could be due to interesting pomegranate like architecture of ZnO coupled with secondary 1-dimensional growth which provided more specific surface area for dye loading.