Synergistic control of ZnO nanostructure morphology and crystallinity via hydrothermal temperature and pH for dye-sensitized solar cells

چکیده مقاله

ZnO nanostructures are attractive for photovoltaic and optoelectronic applications due to their wide bandgap, high exciton binding energy, and chemical stability. This study systematically investigates how hydrothermal synthesis temperature and solution pH govern the morphology, crystallinity, and optoelectronic properties of diverse ZnO nanostructures (nanosheets, nanoflowers, etc.) and their performance in dye-sensitized solar cells (DSSCs). We prepared ZnO through hydrothermal growth at three temperatures (70 °C, 90 °C, and 150 °C) and across a pH range from 9 to 14, characterizing the resulting materials by scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and UV–visible spectroscopy, in addition to current–voltage (I–V) measurements in DSSCs. Our results reveal that precise control of temperature and pH enables the formation of high-surface-area hierarchical morphologies (e.g., flower-like and sheet–sphere assemblies) and enhances crystallinity, thereby improving dye loading, light harvesting, and charge transport. However, elevated hydrothermal temperatures promote coarsening and defect formation, reducing surface area and increasing recombination, thereby diminishing Jsc and overall efficiency. PL analysis reveals a trade-off between near-band-edge and defect-related emission as a function of synthesis conditions, which correlates with device performance. XRD indicates a temperature- and pH-dependent increase in ZnO crystallinity and crystallite size, with phase-pure wurtzite ZnO predominating at higher temperatures and under strongly alkaline conditions. Collectively, the results establish design guidelines for hydrothermally grown ZnO nanostructures in DSSCs and provide mechanistic insight into the structure–property–device performance relationships, highlighting scalable, cost-effective routes for ZnO-based photovoltaic electrodes.