Optical enhancement of amorphous silicon solar cells (original) (raw)
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Assessment of combined TCO/metal rear contact for thin film amorphous silicon solar cells
Solar Energy Materials and Solar Cells, 1995
An optical admittance method is applied to investigate the effect of light absorption enhancement on glass/TCO/p-i-n/TCO/metal type thin film a-Si:H solar cells. The results reveal that a combined TCO/metal as a rear contact for a p-in type thin film a-Si:H solar cell can further increase the integrated absorbance in the active layer of the device. The optimal structure of such a device with the top and rear TCO thin film coatings is discussed.
Algerian Journal of Renewable Energy and Sustainable Development
Hydrogeneted amorphous silicon (a-Si:H) based solar cells are promising candidates for future developments in the photovoltaic industry. In fact, amorphous silicon technology offers significant advantages including low cost fabrication and possibility to deposition on flexible substrat as well as low temperature fabrication. Much progress has been made since the first single junction cell in amorphous silicon made in 1976 by Carlson and Wronski. However, the performance of the solar cells based on a-Si:H is limited by the high defect density and degradation induced by exposure to light, or Staebler-Wronski effect. To become competitive, the performance of the solar cells based on a-Si:H must be improved. In order to improve the performance of a-Si:H solar cells, much research is directed to optimization techniques. The improvement in performance is therefore based on the optimization of the different layers of the solar cell, in particular, the window layer and the absorber layer (i...
Optical modelling of tandem structure amorphous silicon solar cells
Journal of Non-Crystalline Solids, 1998
Using the admittance analysis method, the design of a tandem of two cells stacked one on the top of the other and connected in series is modelled. The i-layer of the top cell is assumed to be made of a-Si:H and that of the bottom cell of a-SiGe:H, and the condition of current matching at maximum power point is applied to determine the tandem's optimal design. The eect of defects as recombination centres is also incorporated in the calculation of the voltage±current dependencies.
Process development of amorphous silicon/crystalline silicon solar cells
Solar Energy Materials and Solar Cells, 1997
We have already investigated some crucial limiting process steps of the amorphous silicon (a-Si)/crystalline silicon (c-Si) solar cell technology and some specific characterization tools of the ultrathin amorphous material used in devices. In this work, we focus our attention particularly on the technology of the ITO front contact fabrication, that also is used as an antireflective coating. It is pointed out that this layer acts as a barrier layer against the diffusion of metal during the annealing treatments of the front contact grid. The criteria of the selection of the metal to be used to obtain good performance of the grid and the deposition methods best suited to the purpose are shown. We were able to fabricate low temperature heterojunction solar cells based p-type Czochralski silicon, and a conversion efficiency of 14.7% on 3.8 cm 2 area was obtained without back surface field and texturization.
Efficient amorphous silicon solar cells: characterization, optimization, and optical loss analysis
Results in Physics, 2017
Hydrogenated amorphous silicon (a-Si:H) has been effectively utilized as photoactive and doped layers for quite a while in thin-film solar applications but its energy conversion efficiency is limited due to thinner absorbing layer and light degradation issue. To overcome such confinements, it is expected to adjust better comprehension of device structure, material properties, and qualities since a little enhancement in the photocurrent significantly impacts on the conversion efficiency. Herein, some numerical simulations were performed to characterize and optimize different configuration of amorphous silicon-based thinfilm solar cells. For the optical simulation, two-dimensional finite-difference time-domain (FDTD) technique was used to analyze the superstrate (p-in) planar amorphous silicon solar cells. Besides, the front transparent contact layer was also inquired by using SnO 2 :F and ZnO:Al materials to improve the photon absorption in the photoactive layer. The cell was studied for open-circuit voltage, external quantum efficiency, and short-circuit current density, which are building blocks for solar cell conversion efficiency. The optical simulations permit investigating optical losses at the individual layers. The enhancement in both short-circuit current density and open-circuit voltage prompts accomplishing more prominent power conversion efficiency. A maximum short-circuit current density of 15.32 mA/cm 2 and an energy conversion efficiency of 11.3% were obtained for the optically optimized cell which is the best in class amorphous solar cell.
The Effect of Hydrogenated Amorphous Silicon on the Optical Properties of Solar Cells
2017
Hydrogenated amorphous silicon (a-Si:H) produced by plasma enhanced chemical vapor deposition (PECVD) is a very interesting material due to the possibility of controlling the energy band gap and the electrical properties by means of the alloy composition. In this work we focused on the intrinsic layer because it is responsible for light absorption and the subsequent charge carrier generation/separation and for photovoltaic stability under continuous illumination (Staebler–Wronski) effect. We have prepared six sample of a-Si:H (i-layer) A, B, C, D, E, F with varied H2 diluted (40, 50, 60, 70 sccm) and the deposition time is varied (30, 40 minutes) and the flow of SiH4 was fixed at 20 sccm. The pressure of chamber MPZ (modular process zones) before deposition process about 5×10 Torr. While during deposition process is 530 mTorr, the deposition temperature is 2700C and RF power is 1.8 watt. To evaluation the optical properties of the thin film we used multiple reflection method (NanoCa...
Progress in Amorphous Silicon Based Solar Cell Technology
As the negative environmental effects of the current use of non-renewable energy sources have become apparent, hydrogenated amorphous silicon (a-Si:H) solar cell technology has advanced to provide a means of powering a future sustainable society. Over the last 25 years, a-Si:H solar cell technology has matured to a stage where there is currently a production of 30 MWpeak/year; and this production capacity continues to increase. The progress is due to the continuous advances made in new materials, cell designs, and large area deposition techniques for mass production. The absence of long-range order result in not only characteristics which make a-Si:H excellent for thin film solar cells, but also provide great flexibility in the design of different solar cell structures and in the manufacturing of large area monolithic modules. A review is presented here of the progress in the development of a-Si:H based materials as well as the evolution of solar cell structures which led to the continuous improvement in their performance and stability.
Solar Energy Materials and Solar Cells, 2010
In this paper, single and multi-junction solar cells based on hydrogenated amorphous silicon (a-Si:H) and its alloy amorphous silicon carbide (a-SiC:H) are analyzed using one dimensional simulator AMPS-1D (Analysis of Microelectronic and Photonic Structures). Effects of thickness and doping concentration of different layers as well as the operating temperature on cell efficiency have been investigated with a view to find a more efficient and stable cell. For the single junction cell, the maximum efficiency of 19.62% has been achieved for a thickness of 500 nm of i-layer, which further improved to 20.8% after the optimization of the doping concentration. In case of double junction cell, the highest efficiency of 20.19% was found for top i-layer thickness of 700 nm after optimizing the bottom cell parameters. For the triple junction cell, parameters of the bottom cell and middle cell were optimized and the maximum efficiency of 21.89% was found with the top i-layer thickness of 600 nm. As regards the operating temperature, the double junction and the triple junction tandem cells showed better stability, with temperature gradient of 0.17% and 0.18%/C, respectively, than the single junction cell of 0.23%/C. The overall investigation on amorphous silicon solar cells as done here gives potential parametric suggestion that may lead to the fabrication of the high efficiency and stabilized a-Si thin film solar cells.
Amorphous Silicon-Based Solar Cells
2010
amorphous silicon [5] with a solar conversion efficiency of about 2.4 % (for historical discussion see ref. [6,7]). Carlson and Wronski's report of the current density vs. output voltage is presented in FIG. 1 (along with the curve from a far more efficient cell reported in 1997 [8]). As these scientists had discovered, the optoelectronic properties of amorphous silicon made by glow discharge (or "plasma deposition") are very much superior to the amorphous silicon thin films prepared, for example, by simply evaporating silicon. After several years of uncertainty, it emerged that plasma-deposited amorphous silicon contained a significant percentage of hydrogen atoms bonded into the amorphous silicon structure, and that these hydrogen atoms were essential to the improvement of the electronic properties of the plasma-deposited material [9]. As a consequence, the improved form of amorphous silicon has generally been known as "hydrogenated amorphous silicon" (or, more briefly, a-Si:H). In recent years, many authors have used the term "amorphous silicon" to refer to the hydrogenated form, which acknowledges that the unhydrogenated forms of amorphous silicon are only infrequently studied today. Why was there so much excitement about the amorphous silicon solar cells fabricated by Carlson and Wronski? First, the technology involved is relatively simple and inexpensive compared to the technologies for growing crystals. Additionally, the optical properties of amorphous silicon are very promising for collecting solar energy, as we now explain. In FIG. 2, the upper panel shows the spectrum for the optical absorption coefficients α(hν) for amorphous silicon and for crystalline silicon [10]. * In the lower panel of the figure, we show the spectrum of the "integrated solar irradiance;" this is the intensity (in W/m 2) of the solar energy carried by photons above an energy threshold hν [11]. We use these spectra to find out how much solar energy is absorbed by layers of varying thickness. The example used in the figure is an a-Si:H layer with a thickness d = 500 nm. Such a layer absorbs essentially all photons with energies greater than 1.9 eV (the energy at which α = 1/d). We then look up how much solar irradiance lies above 1.9 eV. Assuming that reflection of sunlight has been minimized, we find that about 420 W/m 2 is absorbed by the layer (the gray area labeled "absorbed"). 580 W/m 2 of energy is transmitted through such a layer. These energies may be compared to the results for c-Si, for which a 500 nm thick layer absorbs less than 200 W/m 2. To absorb the same energy as the 500 nm a-Si:H layer, a c-Si layer needs to be much thicker. The implication is that much less material is required to make a solar cell from a-Si than from c-Si. † In the remainder of this section we first describe how amorphous silicon solar cells are realized in practice, and we then briefly summarize some important aspects of their electrical characteristics. * We assume familiarity with the concept of a photon energy hν and of an optical absorption coefficient α; see chapter ??. † The very different optical properties of c-Si and a-Si reflect the completely different nature of their electronic states. In solid state physics textbooks, one learns about the "selection rules" that greatly reduce optical absorption in c-Si, which is an "indirect bandgap" semiconductor. Such selections rules do not apply in a-Si. Additionally, the "bandgap" of a-Si is considerably larger than for c-Si.
International Journal of Photoenergy, 2012
The conversion efficiency of a solar cell can substantially be increased by improved material properties and associated designs. At first, this study has adopted AMPS-1D (analysis of microelectronic and photonic structures) simulation technique to design and optimize the cell parameters prior to fabrication, where the optimum design parameters can be validated. Solar cells of single junction based on hydrogenated amorphous silicon (a-Si:H) have been analyzed by using AMPS-1D simulator. The investigation has been made based on important model parameters such as thickness, doping concentrations, bandgap, and operating temperature and so forth. The efficiency of single junction a-Si:H can be achieved as high as over 19% after parametric optimization in the simulation, which might seem unrealistic with presently available technologies. Therefore, the numerically designed and optimized a-SiC:H/a-SiC:H-buffer/a-Si:H/a-Si:H solar cells have been fabricated by using PECVD (plasma-enhanced chemical vapor deposition), where the best initial conversion efficiency of 10.02% has been achieved (V oc = 0.88 V, J sc = 15.57 mA/cm 2 and FF = 0.73) for a small area cell (0.086 cm 2). The quantum efficiency (QE) characteristic shows the cell's better spectral response in the wavelength range of 400 nm-650 nm, which proves it to be a potential candidate as the middle cell in a-Si-based multijunction structures.