Preparation and characterization of ZnO/ZnAl2O4 mixed metal oxide as an effective anode materials for dye-sensitized photodetector / Ethar Yahya Salih

Semiconductor nanomaterials-based photodetectors have attracted considerable attention from various research groups because of their low fabrication cost, easy handling, short carrier-diffusion path length and high density. Photodetector, which is an optoelectronic device, is of growing concern since it can determine the intensity of incident photons by transferring the yielded energy of absorbed light into a measurable electrical signal. Recently, new class photodetector was introduced, namely, dye-sensitized photodetector. Dye-sensitized photodetector has shown great interest among researchers due to its attracting properties such as low fabrication cost and eco-friendly processing. One of the key factors of enhancing the photo-responsive behavior of dye-sensitized photodetector is to develop a deep understanding of each component in this device. Among these component is anode material, which is considered the main component in Dye-sensitized photodetector. The anode material, in dye-sensitized photodetector, serves dual functions; firstly, as a support for sensitizer loading and secondly as a transporter of photo-excited electrons. Therefore, the introduction of new class materials is of great importance. In the present study, Zn/Al layered double hydroxide as precursor was employed with its microstructural features modified. Moreover, ZnO/ZnAl2O4 mixed metal oxides obtained as a result of thermally-treated Zn/Al layered double hydroxide was used as the anode materials due to its superior features such as ultra-fast injection efficiency, similar band gap to ZnO and TiO2, easy manufacturing handling at large scale and relatively large surface area. It was found that the optimum sample (Z6A-MMO-400) exhibited mesoporous surface morphology with value of 53 m2/g surface area which was found to be very sufficient for high dye loading (3.3 x 10-4 mol/cm2). In the UV-Vis analysis, a noticeable red shift towards the visible light was noticed and energy band gap of 3.21 eV was acquired as the thermal treatment temperature increased from 200 to 400 °C. In term of photoluminescence properties, it was observed that both increment in thermal treatment temperature as well as molar ratio resulted in higher ratio. Pristine ZA-LDH exhibted a value of 0.13, whereas Z6A-MMO-400 demonstrated a value of 0.78. The optimum dye-sensitized photodetector Z6A-MMO-400 showed photo-responsivity of 1.1 x 10-2 A/W at 25 mW/cm2, whereas Z6A-MMO-200 and Z3A-MMO-400 exhibited values as low as 2.2 x 10-3 and 1.5 x 10-3 A/W at 25 mW/cm2, respectively. Nonetheless, the response time was calculated to be lower than the recovery time which validates faster electron injection than recombination process. A precise control of the prepared anode materials properties can be used to study and optimize the performance of DS photodetector made of this novel material system