Antireflection coatings based on La doped ZnO and Diamond-like carbon via wet-chemistry and vapor deposition methods for PV Applications /

Abstract

In this era, renewable energy technologies are suitable to meet the challenges of fuel depletion and global warming. One of the potential approaches to mitigate the reliance on fossil fuels is to generate electricity by photovoltaic technology. In recent years, huge advances have been made in the development of photovoltaic technology. Reflection losses of incident light on the Solar cell is an important factor that affects the efficiency of solar cells. Antireflection (AR) coatings can enhance the optical characteristics of Solar Cells. Diamond-like carbon (DLC) has high hardness, is chemically inert, and optically transparent. Due to its superior antireflection properties, DLC films are more suited for photovoltaic technology. Rare earth metal doping in Zinc Oxide can introduce structural defects that help capture light and improve the photocatalytic performance of the Solar Cells. In this work, we synthesized Diamondlike carbon and Lanthanum doped ZnO film via wet chemistry and vapor phase deposition technique. In the first section, we report two different methods to fabricate DLC thin film over the surface of the silicon and FTO substrates via PECVD and Electrodeposition techniques. In the second section, we report the fabrication process of Lanthanum doped ZnO via the sol gel/spin coating method. Various process routes such as the effect of substrate temperature, the effect of voltage, and the effect of concentration of dopants, etc. were studied. Morphological, structural, optoelectrical, and wettability properties of the synthesized film were analyzed by using Scanning Electron Microscopy, FTIR, Raman Spectroscopy, UV-Vis NIR Spectrophotometer, Hall Effect, and Water contact angle measurement, etc. The DLC films were deposited at 2.7, 4, 6, 8, and 10 Volts by electrodeposition route, and it was shown that for a fixed electrolyte concentration and electrode spacing, the applied voltage can be adjusted to obtain varying deposition rates. Likewise, the solution concentration was varied in the 2 vol.% to 10 vol.%, and it was demonstrated that by increasing the solution concentration the deposition rate increases. The increase in the deposition rate was evidenced by an increase in the deposition current as well as the roughness of the films. It was noticed that smaller-sized, well-defined, and more uniform DLC films were obtained at lower concentrations and low voltage levels. The band gap was varied from 2.91 eV to 3.39 eV. Properties of DLC deposited via PECVD also depend on the substrate temperature. DLC deposited at ambient temperature shows high optical transparency throughout the visible and IR region as compared to 100 oC deposited DLC film. In the case of ZnO, studies revealed that ZnO has a wurtzite hexagonal structure and after doping of La into ZnO, reduced the particle size of the films. The bandgap of the doped ZnO was found to vary between 3.22 to 3.29 eV. Synthesized La-doped ZnO thin film shows a hydrophilic property. It clearly showed that the reflection had reduced remarkably after depositing DLC and La-doped ZnO film on the substrate surface. This work demonstrates that DLC and La-doped ZnO films have the potential to be utilized as antireflection layers in photovoltaic applications.