Papers by Keyword: Amorphous Silicon

Abstract: Amorphous Si/SiO₂ quantum wells have been obtained at room temperature with atomic precision using magnetron sputtering. The Si/SiO₂ layer structure induces the higher optical transmittance at the visible wavelength region with increasing layer numbers. The tentative absorption coefficients are evaluated for integrated Si thicknesses. The absorption edge energy dependency on Si layer thickness E₀ = 1.61 + 0.75d^-2 is in accordance with effective mass theory for thicknesses 0.5 < d < 6nm. Quantum confinement effects of the Si/SiO₂ nanostructure layer are confirmed from optical transmittance and reflectance spectra.

Abstract: This document explains and demonstrates how to design efficient amorphous silicon solar cells. Some of the fundamental physical concepts required to interpret the scientific literature about amorphous silicon are introduced. The principal methods such as plasma deposition that are used to make amorphous siliconbased solar cells are investigated. On the basis, high-efficiency solar cells based on amorphous silicon technology are designed. Multi-junction amorphous silicon solar cells are discussed, how these are made and how their performance can be understood and optimized. To conclude this document, some of the directions that are important for future progress in the field are presented.

Abstract: High-efficiency solar cells based on amorphous silicon technology are designed. Multi-junction amorphous silicon solar cells are discussed, how these are made and how their performance can be understood and optimized. Although significant amount of work has been carried out in the last twenty-five years, the Staebler-Wronski effect has limited the development of a-Si:H solar cells. As an alternative material, nc-Si:H has attracted remarkable attention. Taking advantage of a lower degradation in nc-Si:H than a-Si:H and a-SiGe:H alloys, the light induced degradation in triple junction structures has been minimized by designing a bottom-cell-limited current mismatching, and obtained a stable active-area cell efficiency. All this has been investigated in this paper.

Abstract: Al-induced crystallization (AIC) method was used for obtaining polycrystalline silicon (poly-Si) film on glass substrate. The films with glass/a-Si:H/Al structure were fabricated by Plasma Enhanced Chemical Vapor Deposition (PECVD) and magnetic sputtering. Then the samples were sent to perform annealing treatments during the different temperatures and time. The experimental results demonstrate that a highly crystallized poly-Si sample can be achieved by annealing at 480°C for 2h. The crystalline fraction (Xc) of the sample is about 99.1% and the Full Width at Half Maximum (FWHM) is 4.89cm^-1. The average grain size of this sample is about 250nm. The energy dispersive spectroscopy (EDS) measurement confirms that the residual Al in the film is very little.

Abstract: As a high-efficiency silicon solar cell concept amorphous silicon/crystalline silicon (a-Si:H(n,p)/c-Si (p,n)) hetero-junction solar cells are of great scientific interest [1, . The a-Si:H emitter is deposited by plasma-enhanced chemical vapor deposition (PECVD). The biggest challenge is to avoid recombination at the a-Si:H(i)/c-Si interface where the p-n junction is located. A clean, smooth, hydrogen terminated c-Si surface is supposed to be mandatory for a high passivation quality of the deposited layer [3, 4]. It is well established that treatment in dilute hydrofluoric acid (dHF) solution (1-10%) produces a hydrogen-terminated, clean Si surface [e.g. 5, 6, 7]. H-termination is supposed to rise with increasing etch time [8]. Whereas prolonged rinsing after the etch step leads to a formation of OH-groups at the surface [8]. Because of the high sensitivity of the a-Si:H(i)/c-Si interface the influence of prolonged etching in dHF (1%) as well as prolonged rinsing in deionized water (DI water) on the passivation quality of the deposited a-Si:H(i) layer has to be carefully studied. Also the possibility of decreased hydrophobicity and a possible iron recontamination from the HF has been taken into account.

Abstract: A new structure of a-Si/ poly-Si tandem solar cell has been desiged and prepared. Amorphous silicon has been use as photovoltaic material of bottom cell. And polysilicon has been used as photovoltaic material of bottom cell.The combination of amorphous silicon and polysilicon extends the light range which can be used by solar cell. This structure improves the efficiency of solar cell greatly.

Abstract: Solar cells employing heterojunction emitters of amorphous silicon (a-Si) on a monocrystalline silicon (c-Si) substrate have demonstrated high efficiencies without requiring high-temperature processing [. An example of such a cell structure is shown in Figure 1. It has been found that the cell efficiency can be boosted by inserting a thin undoped (intrinsic) a-Si layer between the a-Si emitter and the c-Si substrate. The thin intrinsic layer provides very good passivation of interface defects, thus reducing the surface recombination velocity.

Abstract: Simple two-step wet-chemical cleans composed of an oxidizing step with in water dissolved ozone followed by an etching step have been studied for high-efficient hetero-junction silicon solar cell applications. For this purpose flat Si (111) samples passivated with amorphous silicon have been investigated. The effect of nanoroughness of the crystalline silicon surface on the minority carrier lifetime is shown. An influence of the storage time between cleaning and a-Si:H deposition was found and can partly be attributed to changes in surface roughness and native oxide growth.

Abstract: Density of states in the channel bulk area of a-Si:H thin-film transistors (TFTs) was extracted by using low-frequency noise analysis. The drain current noise power spectral density shows 1/ƒγ behavior at relatively high frequencies (ƒ > 1 kHz), which is due to the exponential distribution of tail states. For the analysis, the modified number fluctuation model which is correlated with mobility fluctuation was used. From the relationship (γ=1- kT/Et ) between exponent γ and the slope of exponential distribution Et of band tail states, the distribution of the band tail near conduction band was extracted.

Abstract: Two-dimensional simulation in Plasma Enhanced Chemical Vapor Deposition (PECVD) is conducted by using multi-physics analysis method. Simulation results show the growth process of amorphous silicon thin film in the PECVD reactor. The effect of process parameters (such as power supply power, electrode spacing, etc.) on the deposition rate and electric field strength is obtained, and the optimum conditions needed for growth of amorphous silicon thin film is achieved as well. It was experimentally proved that the simulation results are consistent with the experimental results, and provide a theoretical basis for adjusting and optimizing the film preparation process.