Microemulsion-assisted Zinc Oxide Synthesis: Morphology Control and Its Applications in Photoanodes of Dye-Sensitized Solar Cells

Zinc oxide (ZnO) crystals with structures of hexagonal club (HC), nanoparticle (NP), and hexagonal plate (HP) are synthesized via microemulsion technique by using the surfactants of cationic cetylmethylammonium bromide (CTAB), nonionic Triton^® X-100, and anionic docusate sodium (AOT), respectively, and they are used for the photoanodes of dye-sensitized solar cells (DSSCs). Phase diagrams are constructed in mapping the compositions of the microemulsions to guide the synthesis of ZnO crystals. All the synthesized ZnO crystals exhibited wurtzite crystal phase of ZnO in their X-ray diffraction (XRD) patterns, and their morphologies and structures were investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM), respectively. The sub-micro sized HC and HP ZnO crystals are meritorious in the present work as large particles are effective for light-scattering in the photoanode; the nano-sized NP ZnO crystal is meritorious in the present work as small particles are effective for dye adsorption in the photoanode of DSSCs. By using the photoanodes with bi-layer NPs/HPs and NPs/HCs ZnO films for the ZnO-based DSSCs with a novel organic dye (coded DJ149), we obtained good cell efficiencies of 7.40% and 6.95%, respectively. Incident photon-to-current conversion efficiency (IPCE) curves, and UV-vis reflectance spectra are also used to substantiate the results.