Optimization of processing parameters on the controlled growth of ZnO nanorod arrays for the performance improvement of solid-state dye-sensitized solar cells

High-transparency and high quality ZnO nanorod arrays were grown on the ITO substrates by a two-step chemical bath deposition (CBD) method. The effects of processing parameters including reaction temperature (25-95 oC) and solution concentration (0.01-0.1 M) on the crystal growth, alignment, optical and electrical properties were systematically investigated. It has been found that these process parameters are critical for the growth, orientation and aspect ratio of the nanorod arrays, showing different structural and optical properties. Experimental results reveal that the hexagonal ZnO nanorod arrays prepared under reaction temperature of 95 oC and solution concentration of 0.03 M possess highest aspect ratio of ∼21, and show the well-aligned orientation and optimum optical properties. Moreover the ZnO nanorod arrays based heterojunction electrodes and the solid-state dye-sensitized solar cells (SS-DSSCs) were fabricated with an improved optoelectrical performance. -- Graphical abstract: The ZnO nanorod arrays demonstrate well-alignment, high aspect ratio (L/D∼21) and excellent optical transmittance by low-temperature chemical bath deposition (CBD). Display Omitted Research highlights: → Investigate the processing parameters of CBD on the growth of ZnO nanorod arrays. → Optimization of CBD process parameters: 0.03 M solution concentration and reaction temperature of 95 oC. → The prepared ZnO samples possess well-alignment and high aspect ratio (L/D∼21). → An n-ZnO/p-NiO heterojunction: great rectifying behavior and low leakage current. → SS-DSSC has JSC of 0.31 mA/cm2 and VOC of 590 mV, and an improved η of 0.059%.