Search

Today, silicon solar cells (amorphous films and wafer-based) are a main source of green energy. These cells and their components are produced by employing various technologies. Unfortunately, during the production process, chemicals that are harmful for the environment and for human life are used. For example, hydrofluoric acid is used to texture the top electrode to improve light harvesting. In this work, and also in recent ones, we report a way to obtain 3D textures on the top electrode by using zinc oxide nanorods. The efficiency of a textured solar cell structure is compared with the one obtained for a planar zinc oxide/silicon structure. The present results show the possibility to produce efficient solar cells on a relatively thin 50 μm thick silicon substrate. Solar cells with structured top electrodes were examined by numerous measuring techniques. Scanning electron microscopy revealed a grain-like morphology of the magnesium-doped zinc oxide film. The size of the grains is closely related to the structure of the nanorods. The external quantum efficiency of the cells was measured. The obtained solar cell shows response in a wide spectral range from ultraviolet to infrared. Current–voltage and current–voltage–temperature measurements were performed to evaluate basic photovoltaic parameters. At room temperature, the cells efficiency equals to 9.1% for textured structures and 5.4% for planar structures, respectively. The work, therefore, describes an environmentally friendly technology for PV architecture with surface textures increasing the efficiency of PV cells.

In order to effectively utilize the photovoltaic properties of gallium arsenide, its surface/interface needs to be properly prepared. In the experiments described here we examined eight different paths of GaAs surface treatment (cleaning, etching, passivation) which resulted in different external quantum efficiency (EQE) values of the tested photovoltaic (PV) cells. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) examinations were conducted to obtain structural details of the devices. X-ray photoelectron spectroscopy (XPS) with depth profiling was used to examine interface structure and changes in the elemental content and chemical bonds. The photoluminescence (PL) properties and bandgap measurements of the deposited layers were also reported. The highest EQE value was obtained for the samples initially etched with a citric acid-based etchant and, in the last preparation step, either passivated with ammonium sulfide aqueous solution or treated with ammonium hydroxide solution with no final passivation. Subsequent I–V measurements, however, confirmed that from these samples, only the sulfur-passivated ones provided the highest current density. The tested devices were fabricated by using the ALD method.

Titanium nitride is a well-known conductive ceramic material that has recently experienced resumed attention because of its plasmonic properties comparable to metallic gold and silver. Thus, TiN is an attractive alternative for modern and future photonic applications that require compatibility with the Complementary Metal-Oxide-Semiconductor (CMOS) technology or improved resistance to temperatures or radiation. This work demonstrates that polycrystalline TiNx films sputtered on silicon at room temperature can exhibit plasmonic properties continuously from 400 nm up to 30 μm. The films’ composition, expressed as nitrogen to titanium ratio x and determined in the Secondary Ion Mass Spectroscopy (SIMS) experiment to be in the range of 0.84 to 1.21, is essential for optimizing the plasmonic properties. In the visible range, the dielectric function renders the interband optical transitions. For wavelengths longer than 800 nm, the optical properties of TiNx are well described by the Drude model modified by an additional Lorentz term, which has to be included for part of the samples. The ab initio calculations support the experimental results both in the visible and infra-red ranges; particularly, the existence of a very low energy optical transition is predicted. Some other minor features in the dielectric function observed for the longest wavelengths are suspected to be of phonon origin.

The use of plasmonic inclusions in heterojunction solar cells promises increase of solar-to-electric energy conversion efficiency. Recently, solar cells with ZnO nanorods attracted a lot of attention due to improved efficiency provided by highly scattering ZnO nanostructures on silicon or perovskite. N-type ZnO nanorods are grown on p-Si monocrystalline 180 μm thick substrates among others by means of a hydrothermal technique which requires prior seeding by deposition of thin film of ZnO or noble metals. In the latter case, naturally formed metal islands can also act as plasmonic nanoparticles (NPs). Excitation of plasmonic resonance on the NPs leads to directional scattering of light towards Si layer and electromagnetic field enhancement at their vicinity, close to the ZnO-Si junction, what results in improved energy absorption in the semiconductor layer and thus energy conversion efficiency. In this study, we investigate optimal conditions at which plasmonic phenomenon further improves light trapping in the Si-ZnO solar cells. In simulations performed by means of 3D FDTD method, we calculate light absorption enhancement in the system due to plasmonic NPs used as a seed layer at the ZnO/Si. In the calculations Ag, and Al NPs of different size and geometry close to that achievable in the experiment are analyzed. Finally, numerical results taking into account the granulometry of metal NPs achieved in the experiment are compared with the efficiency of fabricated cells.

The future applications of hyperbolic metamaterials demand stacks of materials with alternative ultra-thin conductive/dielectric films with good homogeneity of the thickness and reduced roughness level. In this work, the technology of pulsed-DC magnetron sputtering of aluminum was optimized using the Taguchi method in order to fabricate Al films with improved roughness level. The performed structural characterization proved the smaller Al domains and better homogeneity of the surface. The optimized process was used to fabricate a multilayer structure of Al/HfOx as the metamaterial media. The fabricated structures were optically characterized in the UV/VIS range. The presented findings demonstrated the tunability effect of the effective reflectance of the examined stacks. The presented results are promising for the future application of multilayer structures in novel photonic devices based on hyperbolic metamaterials.

Structured Silicon layers are used to improve light harvesting by Si-based solar cells. Microstructure of Si is obtained by a selective Si etching using aggressive solvents (acids like HF). In the approach discussed in this work a simplified architecture of solar cells is discussed. A structured electrode is formed by deposition of ZnO nanorods on top of p-type Si. This modification eliminates energy consuming and environmental unfriendly technological steps, as discussed. The so-obtained 3D top electrode consists of n-type ZnO:Al (AZO) layer grown on ZnMgO coated zinc oxide nanorods. AZO and ZnMgO films are deposited by Atomic Layer Deposition method (ALD). Advantages of this technique are first discussed. Several possible applications of the ALD are reviewed.