Using the light scattering properties of multi-textured AZO films on inverted hemisphere textured glass surface morphologies to improve the efficiency of silicon thin film solar cells (original) (raw)
Energy Procedia, 2015
In the thin-film photovoltaic industry, to achieve a high light scattering in one or more of the cell interfaces is one of the strategies that allow an enhancement of light absorption inside the cell and, therefore, a better device behavior and efficiency. Although chemical etching is the standard method to texture surfaces for that scattering improvement, laser light has shown as a new way for texturizing different materials, maintaining a good control of the final topography with a unique, clean, and quite precise process. In this work AZO films with different texture parameters are fabricated. The typical parameters used to characterize them, as the root mean square roughness or the haze factor, are discussed and, for deeper understanding of the scattering mechanisms, the light behavior in the films is simulated using a finite element method code. This method gives information about the light intensity in each point of the system, allowing the precise characterization of the scattering behavior near the film surface, and it can be used as well to calculate a simulated haze factor that can be compared with experimental measurements. A discussion of the validation of the numerical code, based in a comprehensive comparison with experimental data is included.
Applied Physics A, 2015
Various SF 6 /Ar plasma-textured periodic glass surface morphologies for high transmittance, haze ratio and low sheet resistance of ITO:Zr films are reported. The SF 6 /Ar plasma-textured glass surface morphologies were changed from low aspect ratio to high aspect ratio with the increase in RF power from 500 to 600 W. The micro-and nano-size features of textured glass surface morphologies enhanced the haze ratio in visible as well as NIR wavelength region. Micro-size textured features also influenced the sheet resistance and electrical characteristics of ITO:Zr films due to step coverage. The ITO:Zr/AZO bilayer was used as front TCO electrode for p-i-n amorphous silicon thin film solar cells with current density-voltage characteristics as: V oc = 875 mV, FF = 70.90 %, J sc = 11.31 mA/cm 2 , g = 7.02 %.
Analysis of the scattering properties of textured TCO structures for thin film silicon solar cells
The texture of transparent conducting oxides (TCO) plays an important role for the performance of amorphous (a-Si:H) and microcrystalline (µc-Si:H) thin-film silicon solar cells. Different TCO morphologies and feature sizes lead to different light in-coupling, light trapping, and absorbance in the cell. Induced by TCO scattering, the light path is enhanced which results in a higher absorbance in the silicon layer. We have investigated the scattering properties of sputtered and post-etched ZnO substrates. Varying the etching time results in different feature sizes. To find relations between the surface topology and the scattering behaviour we developed a model, which allows for an analysis of the surface morphology and the simulation of the angle resolved scattering behaviour of randomly textured TCOs. The model uses atomic force microscope data and is based on geometric optics. In this article experimental and simulated results are analysed and discussed.
Light scattering at nano-textured surfaces in thin film silicon solar cells
2010
State-of-the-art solar cells based on thin film silicon make use of random textures for absorption enhancement; in the past, the development of these textures was carried out empirically, and in most applications this is still the case. Attempts to understand light scattering at the internal interfaces rely on quantities like haze and angle resolved scattering that are only measurable in air and need to be extrapolated, normally by means of scalar scattering theory. In this context it is unfortunate that the description of scattering into air requires modifications with empiric parameters whose scaling is unknown. We present an alternate approach for predicting angular properties and intensities of scattered light which is based only on measurable quantities like the surface morphology and the refractive index dispersion, no adjustable parameters are needed.
Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III, 2014
Light scattering at randomly textured interfaces is essential to improve the absorption of thin-film silicon solar cells. Aluminium-induced texture (AIT) glass provides suitable scattering for amorphous silicon (a-Si:H) solar cells. The scattering properties of textured surfaces are usually characterised by two properties: the angularly resolved intensity distribution and the haze. However, we find that the commonly used haze equations cannot accurately describe the experimentally observed spectral dependence of the haze of AIT glass. This is particularly the case for surface morphologies with a large rms roughness and small lateral feature sizes. In this paper we present an improved method for haze calculation, based on the power spectral density (PSD) function of the randomly textured surface. To better reproduce the measured haze characteristics, we suggest two improvements: i) inclusion of the average lateral feature size of the textured surface into the haze calculation, and ii) considering the opening angle of the haze measurement. We show that with these two improvements an accurate prediction of the haze of AIT glass is possible. Furthermore, we use the new equation to define optimum morphology parameters for AIT glass to be used for a-Si:H solar cell applications. The autocorrelation length is identified as the critical parameter. For the investigated a-Si:H solar cells, the optimum autocorrelation length is shown to be 320 nm.
Design of ZnO:Al films with optimized surface texture for silicon thin-film solar cells
Proceedings of the SPIE - The International Society for Optical Engineering, 2006
This study addresses the design of radio frequency (rf) magnetron sputtered aluminum doped zinc oxide (ZnO:Al) front contacts for silicon thin-film solar cells. Optimized films comprise high conductivity and transparency, as well as a surface topography trapping the light within the photovoltaically active layers. We have investigated the influence of the doping level of the target as well as the substrate temperature during sputter deposition on the ZnO:Al properties. The aluminum content in the target influences the transmission in the near infrared (NIR), the conductivity as well as the film growth of the ZnO:Al layer. The latter affects the surface topography which develops during wet-chemical etching in diluted hydrochloric acid. Depending on aluminum content in the target and heater temperature three different regimes of etching behavior have been identified. We have applied the ZnO:Al films as front contacts in thin-film silicon solar cells to study their light trapping ability. While high transparency is a prerequisite, the light trapping has been improved using front contacts with a surface topography consisting of relatively uniformly dispersed craters. We have identified low amount of target doping and high substrate temperatures as sputter parameters enabling high cell currents. Short-circuit current densities of up to 26.8 mA/cm 2 have been realized in µc-Si:H single junction cell with absorber layer thickness of 1.9 µm.
Influence of the Angle of Incident Light on the Performance of Textured Silicon Solar Cells
Journal of Nano- and Electronic Physics, 2021
It is important to study environmental effects on the properties of solar cells because solar cells are usually used in open environments. If the surface morphology of a solar cell changes, the angle of incident light will change depending on its photoelectric properties. So, in this paper, the photoelectric properties of silicon solar cells covered with upright pyramids with different base angles were investigated depending on the angle of incident light. From the obtained results, it was found that when the angle of incident light is varied from 0 to 80, the short circuit current densities of planar and pyramidal textured silicon solar cells with base angles of pyramids of 50.4 and 70.4 decrease to 82.6, 88.8, 89.8 %, the open circuit voltages decrease to 10.5, 12.8, 14.1 % and the fill factors decrease to 1.9, 2.2 and 3.2 %. The efficiency of a silicon solar cell covered with pyramids with a base angle of 70.4 0 is better than those of planar and other textured silicon solar cells in the range of incident light angles from 0 to 80, although the dependence of its photoelectric parameters on the angle of incident light increases.
International Journal of Photoenergy, 2015
Microcrystalline silicon ( c-Si:H) thin-film solar cells are processed on glass superstrates having both micro-and nanoscale surface textures. The microscale texture is realised at the glass surface, using the aluminium-induced texturing (AIT) method, which is an industrially feasible process enabling a wide range of surface feature sizes (i.e., 700 nm-3 m) of the textured glass. The nanoscale texture is made by conventional acid etching of the sputter-deposited transparent conductive oxide (TCO). The influence of the resulting "double texture" on the optical scattering is investigated by means of atomic force microscopy (AFM) (studying the surface topology), haze measurements (studying scattering into air), and short-circuit current enhancement measurements (studying scattering into silicon). A predicted enhanced optical scattering efficiency is experimentally proven by a short-circuit current enhancement Δ sc of up to 1.6 mA/cm 2 (7.7% relative increase) compared to solar cells fabricated on a standard superstrate, that is, planar glass covered with nanotextured TCO. Enhancing the autocorrelation length (or feature size) of the AIT superstrates might have the large potential to improve the c-Si:H thin-film solar cell efficiency, by reducing the shunting probability of the device while maintaining a high optical scattering performance.
Microcrystalline silicon (uc-Si:H) thin-film solar cells are processed on glass superstrates having both micro-and nanoscale surface textures. The microscale texture is realised at the glass surface, using the aluminium-induced texturing (AIT) method, which is an industrially feasible process enabling a wide range of surface feature sizes (i.e., 700 nm–3 um) of the textured glass. The nanoscale texture is made by conventional acid etching of the sputter-deposited transparent conductive oxide (TCO). The influence of the resulting " double texture " on the optical scattering is investigated by means of atomic force microscopy (AFM) (studying the surface topology), haze measurements (studying scattering into air), and short-circuit current enhancement measurements (studying scattering into silicon). A predicted enhanced optical scattering efficiency is experimentally proven by a short-circuit current enhancement ΔIsc of up to 1.6 mA cm^-2 (7.7% relative increase) compared to ...
Texturing, reflectivity, diffuse scattering and light trapping in silicon solar cells
Energy conversion efficiency is a critical consideration in the application of silicon solar cells. Texturing of both the front side and the backside of silicon solar cells has been used in the past to increase the absorption of infrared sun light energy in silicon solar cells. A review is given of some of the basic concepts and then a design described for the optimal textured structure that can result in improvements in conversion efficiency of up to 20% on crystalline silicon solar cells and up to 40% on thin film silicon solar cells. Some of the practical limitations are described in realizing these structures in silicon technology.
Journal of Materials Science: Materials in Electronics, 2018
In this study, we report a single heterojunction solar cell based on n-type zinc oxide/p-type silicon. Three different solar cells were fabricated based on ZnO thin film on Si substrate, ZnO nanorods on Si substrate, and ZnO nanorods on micropyramidal structure of Si substrate. The comparison between these three kinds of solar cells was studied. Pyramidal structure of silicon was fabricated using chemical etching technique of p-type Si (100). The chemical solution consists of NaOH, isopropyl alcohol and hydrazine hydrate. The results showed that Si micro-pyramids can enhance optical absorption of Si substrates by increasing surface area and entrapping of incident light. For fabrication of uniform ZnO nanorods, a seed layer of ZnO was deposited on Si substrates via radio frequency magnetron sputtering technique. This layer can be used as an active n-type material in heterojunction solar cells as well. ZnO nanostructures can increase light absorption due to their high specific surface area. The combination of ZnO nanorods and Si micro-pyramids can enhance light trapping effect and increase the efficiency of solar cells. The structural and morphology of samples were studied using field-emission scanning electron microscopy, atomic force microscopy and X-ray diffractometry while the optical properties were investigated using photoluminescence and reflectance spectrometry. The efficiency and fill factor of solar cells were obtained from current-voltage characteristics using a solar simulator and a source-meter. The results showed that the efficiency of solar cell based on nanostructures of ZnO/micropyramids of Si is highly increased due to high anti-reflective behavior of this sample.
Journal of Energy and Natural Resources, 2015
We have introduced an approach to establish a methodology for 3D optical simulation that allows analyzing optical losses in the individual layers of a thin-film solar cell structure. Using commercial Finite-Difference Time-Domain (FDTD) tool, where Maxwell's Curl equations were rigorously solved for optimizing such cells, a computer modeling has been performed. We have reported the ways to investigate efficient light-trapping schemes by using periodically textured transparent conductive oxide (TCO) in thin-film amorphous silicon solar cells. The optical effects in small area thin film silicon p-in solar cells deposited on glass substrates coated with aluminum doped zinc oxide (ZnO:Al) have been addressed. In order to enhance the efficiency, TCO surface morphology has been analyzed, where pyramidal and parabolic textured surfaces have been used. For these cells, the quantum efficiency, short-circuit current, total reflectance, and all absorption losses have been successfully computed and analyzed. The investigation was carried out based on our proposed model that exhibits maximum current density of 17.32 mA/cm 2 for the absorbing layer thickness of 300 nm.
The preparation of thin film silicon solar cells containing Ag nanoparticles is reported in this article. Ag nanoparticles were deposited on fluorine doped tin oxide coated glass substrates by the evaporation and condensation method. a-Si:H solar cells were deposited on these substrates by cluster type plasma enhanced chemical vapor deposition. We discuss the double textured surface effect with respect to both the surface morphology of the substrate and the plasmonic effect of the Ag nanoparticles. Ag nanoparticles of various sizes from 10 to 100 nm were deposited. The haze values of the Ag embedded samples increased with increasing particle size whereas the optical transmittance decreased at the same conditions. The solar cell with the 30 nm size Ag nanoparticles showed a short circuit current density of 12.97 mA/cm 2 , which is 0.53 mA/cm 2 higher than that of the reference solar cell without Ag nanoparticles, and the highest quantum efficiency for wavelengths from 550 to 800 nm. When 30 nm size nanoparticles were employed, the conversion efficiency of the solar cell was increased from 6.195% to 6.696%. This study reports the application of the scattering effect of Ag nanoparticles for the improvement of the conversion efficiency of amorphous silicon solar cells.
Optical scattering properties of a nano-textured ZnO-silicon interface
International Conference on Applications of Optics and Photonics, 2011
The scattering properties of transparent conductive oxide (TCO) layers are fundamentally related to the performance of thin film silicon solar cells. In this study we introduce an experimental technique to access light scattering properties at textured TCO-silicon interfaces. Therefore we prepared a sample with a polished microcrystalline silicon layer, which is deposited onto a rough TCO layer. We used the measured results to validate calculations obtained with rigorous diffraction theory, i.e. a numerical solution of Maxwell's equations. Furthermore we evaluated four approximate models based on the scalar scattering theory and ray tracing and compared them to the rigorous diffraction theory.
2011
ZnO:Al films deposited at 250 1C on Corning glass by radio frequency magnetron sputtering were studied for their use as front contact for thin film silicon solar cells. For this purpose, a two-step etching method combining different concentrations of diluted hydrochloric acid (from 0.1% to 3%) with different etching times was developed. Its influence on morphological, electrical and optical properties of the etched films was evaluated. This new etching method led to more uniform textured surfaces, where the electrical properties remained unchangeable after the etching process, and with adapted light scattering properties similar to those exhibited by commercial substrates.
Optimization of textured-dielectric coatings for crystalline-silicon solar cells
Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996, 1996
We report on the optimization of textured-dielectric coatings for reflectance control in crystalline-silicon (c-Si) photovoltaic modules. Textured-dielectric coatings reduce encapsulated-cell reflectance by promoting optical confinement in the module encapsulation; i.e., the textured-dielectric coating randomizes the direction of rays reflected from the dielectric and from the c-Si cell so that many of these reflected rays experience total internal reflection at the glass-air interface. Some important results of this work include the following: we demonstrated textured-dielectric coatings (ZnO) deposited by a highthroughput low-cost deposition process; we identified factors important for achieving necessary texture dimensions; we achieved solar-weighted extrinsic reflectances as low as 6% for encapsulated c-Si wafers with optimized textured-ZnO coatings; and we demonstrated improvements in encapsulated cell performance of up to 0.5% absolute compared to encapsulated planar cells with single-layer antireflection coatings.