Effect of Annealing Temperature on ECD Grown Hexagonal-Plane Zinc Oxide

Zinc oxide (ZnO) offers a great potential in several applications from sensors to Photovoltaic cells thanks to the material’s dependency, to its optical and electrical properties and crystalline structure architypes. Typically, ZnO powder tends to be grown in the form of a wurtzite structure allowing versatility in the phase of material growths; albeit, whereas in this work we introduce an alternative in scalable yet relatively simple 2D hexagonal planed ZnO nanoflakes via the electrochemical deposition of commercially purchased Zn(NO3)2 and KCl salts in an electrochemical process. The resulting grown materials were analyzed and characterized via a series of techniques prior to thermal annealing to increase the grain size and improve the crystal quality. Through observation via scanning electron microscope (SEM) images, we have analyzed the statistics of the grown flakes’ hexagonal plane’s size showing a non-monotonal strong dependency of the average flake’s hexagonal flakes’ on the annealing temperature, whereas at 300 °C annealing temperature, average flake size was found to be in the order of 300 μm2. The flakes were further analyzed via transmission electron microscopy (TEM) to confirm its hexagonal planes and spectroscopy techniques, such as Raman Spectroscopy and photo luminescence were applied to analyze and confirm the ZnO crystal signatures. The grown materials also underwent further characterization to gain insights on the material, electrical, and optical properties and, hence, verify the quality of the material for Photovoltaic cells’ electron collection layer application. The role of KCl in aiding the growth of the less preferable (0001) ZnO is also investigated via various prospects discussed in our work. Our method offers a relatively simple and mass-producible method for synthesizing a high quality 2D form of ZnO that is, otherwise, technically difficult to grow or control

Surface Enhanced Raman Scattering in Graphene Quantum Dots Grown via Electrochemical Process

Graphene Quantum dots (GQDs) are used as a surface-enhanced Raman substrate for detecting target molecules with large specific surface areas and more accessible edges to enhance the signal of target molecules. The electrochemical process is used to synthesize GQDs in the solution-based process from which the SERS signals were obtained from GQDs Raman spectra. In this work, GQDs were grown via the electrochemical process with citric acid and potassium chloride (KCl) electrolyte solution to obtain GQDs in a colloidal solution-based format. Then, GQDs were characterized by transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy, respectively. From the results, SERS signals had observed via GQDs spectra through the Raman spectra at D (1326 cm−1) and G (1584 cm−1), in which D intensity is defined as the presence of defects on GQDs and G is the sp2 orbital of carbon signal. The increasing concentration of KCl in the electrolyte solution for 0.15M to 0.60M demonstrated the increment of Raman intensity at the D peak of GQDs up to 100 over the D peak of graphite. This result reveals the potential feasibility of GQDs as SERS applications compared to graphite signals

A Multi-Electron Transporting Layer for Efficient Perovskite Solar Cells

In this work, a multi-electron transporting layer (ETL) for efficient perovskite solar cells is investigated. The multi-ETL consists of five conditions including SnO2, SnO2/SnOx, TiO2, TiO2/SnO2, and TiO2/SnO2/SnOx. The best performance of PSC devices is found in the SnO2/SnOx double-layer and exhibits a power conversion efficiency equal to 18.39% higher than the device with a TiO2 single-layer of 14.57%. This enhancement in efficiency can be attributed to a decrease in charge transport resistance (Rct) and an increase in charge recombination resistance (Rrec). In addition, Rct and Rrec can be used to explain the comparable power conversion efficiency (PCE) between a PSC with a SnO2/SnOx double-layer and a PSC with a triple-layer, which is due to the compensation effect of Rct and Rrec parameters. Therefore, Rct and Rrec are good parameters to explain the efficiency enhancement in PSC. Thus, the Rct and Rrec from the electrochemical impedance spectroscopy (EIS) technique is an easy and alternative way to obtain information to understand and characterize the multi-ETL on PSC