Fabrication of Polycrystalline Silicon Films from SiF4/H2/SiH4Gas Mixture Using Very High Frequency Plasma Enhanced Chemical Vapor Deposition with In Situ Plasma Diagnostics and Their Structural Properties (original) (raw)
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Modern Physics Letters B, 2001
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Solar Energy Materials and Solar Cells, 2003
This review article gives a comprehensive compilation of recent developments in low temperature deposited poly Si films, also known as microcrystalline silicon. Important aspects such as the effect of ions and the frequency of the plasma ignition are discussed in relation to a high deposition rate and the desired crystallinity and structure. The development of various ion energy suppression techniques for plasma enhanced chemical vapour deposition and ionless depositions such as HWCVD and expanding thermal plasma, and their effect on the material and solar cell efficiencies are described. The recent understanding of several important physical properties, such as the type of electronic defects, structural effects on enhanced optical absorption, electronic transport and impurity incorporation are discussed. For optimum solar cell efficiency, structural considerations and predictions using computer modelling are analysed. A correlation between efficiency and the two most important process parameters, i.e., growth rate and process temperature is carried out. Finally, the application of these poly Si cells in multijunction cell structures and the best efficiencies worldwide by various deposition techniques are discussed.
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International Journal of Hydrogen Energy, 2008
Among the most promising technological alternatives for the development of photovoltaic modules and cells of a low cost, good energetic conversion and feasibility for mass production, polycrystalline silicon thin film solar cells deposited directly on a transparent substrate are currently being considered the best. We have developed in our laboratory a PECVD reactor capable of producing the deposition of amorphous hydrogenated silicon at rates of above 2 nm/seg, allowing a significant production per line on the plant. Discharge gas is silane, to which diborane or phosphine is added so as to form the cell. Basically, work is done on a structure of cell type TCO/n+/pÀ/p+/M, which has 2 mm of total thickness. Schott AF-37 glass is used as a substrate, for their ability to withstand temperatures of up to 800 1C. The amorphous cell is subsequently annealed at gradual temperatures of 100 1C to achieve dehydrogenation up to 650-700 1C for 12 h until their complete crystallization is achieved. Our results show a complete crystallization of silicon with a grain size of less than a micron, with a dehydrogenation process at 500 1C, leaving a remainder of less than 1% in hydrogen as monohydrate. The parameters of the cell estimated from the IV curve yield low values, FFo0.55, Icc o200 mA and Voco420 mV. The high series resistance is due to the grain size and defect density, which will be attempted to be improved by post-hydrogenation and rapid thermal annealing (RTA) methods at high temperatures.
Manufacturing of a-Si/μc-Si thin-film solar cell using PECVD and silver coating
2018
Thin films of mixed amorphous/microcrystalline-phases have been researched during the last decade for manufacturing silicon solar cells. In this work, the Plasma Enhanced Chemical Vapor Deposition PECVD process parameters; namely, dilution ratios and substrate temperature were controlled to build a p-i-n integrated junction at low dilution ratios with moderate substrate temperatures. In the first part of this work, an intrinsic layer was deposited on Indium Tin Oxide ITO glass by PECVD technique with different dilution ratios of silane in hydrogen to study the transition from amorphous to microcrystalline phase. Based on the results of this work, and in order to study the efficiency of the solar cell and the optical properties, the second part of the work included applying a layer of nano-silver by PVD technique at a range of temperatures up to 250C on one selected i-layer condition at a H2/SiH4 gas dilution ratio of 13.3 at 250C. The Si thin film was evaluated by field emission s...
IEEE Transactions on Electron Devices, 2012
The optical emission spectrometer (OES) is an effective experimental tool for monitoring plasma states and the composition of gases during the growth of silicon thin films by plasma-enhanced chemical vapor deposition. In this paper, hydrogenated amorphous silicon (a-Si) (a-Si:H) and microcrystalline silicon (µc-Si) thin films have been deposited in a parallel-plate radio frequency (RF) plasma reactor using silane and hydrogen gas mixtures. The plasma emission atmosphere was recorded using an OES system during the growth of the Si thin films. The plasma was simultaneously analyzed during the process using an OES method to study the correlation between growth rate and microstructure of the films. In the deposition, the emitted species (SiH * , Si * , and H *) were analyzed. The OES analysis supported a chemisorption-based deposition model of the growth mechanism. The effects of RF power, electron-to-substrate distance, and H 2 dilution of the emission intensities of excited SiH, Si, and H on the growth rate and microstructures of the film were studied. Finally, single-junction a-Si:H and µc-Si solar cells were obtained with initial aperture area efficiencies of 9.71% and 6.36%, respectively. A tandem a-Si/µc-Si cell was also realized with an efficiency of 12.3%. Index Terms-Amorphous/microcrystalline silicon (a-Si/µc-Si) thin films, optical emission spectrometer (OES), plasma-enhanced chemical vapor deposition (PECVD). I. INTRODUCTION A T PRESENT, several research institutions are active in the research and development of various thin-film silicon solar cells. Process technology, yield rate, and the efficiency of cells are all gradually being improved. Currently, the most Manuscript
High-rate deposition of a-Si:H thin layers for high-performance silicon heterojunction solar cells
Progress in Photovoltaics: Research and Applications, 2013
In this paper, we describe a technique for high-quality interface passivation of n-type crystalline silicon wafers through the growth of hydrogenated amorphous Si (a-Si:H) thin layers using conventional plasma-enhanced chemical vapor deposition. We investigated the onset of crystallization of the a-Si:H layers at various deposition rates and its effect on the surface passivation properties. Epitaxial growth occurred, even at a low substrate temperature of 90 C, when the deposition rate was as low as 0Á5 Å/s; amorphous growth occurred at temperatures up to 150 C at a higher deposition rate of 4Á2 Å/s. After optimizing the intrinsic a-Si:H layer deposition conditions and then subjecting the sample to post-annealing treatment, we achieved a very low surface recombination velocity (7Á6 cm/s) for a double-sided intrinsic a-Si:H coating on an n-type crystalline silicon wafer. Under the optimized conditions, we achieved an untextured heterojunction cell efficiency of 16Á7%, with a high open-circuit voltage (694 mV) on an n-type float-zone Si substrate. On a textured wafer, the cell efficiency was further enhanced to 19Á6%.
Crystalline Silicon (Si) based solar cells are dominating the photovoltaic market and the situation is likely to continue for the next decades. Microelectronic concepts and processes were transferred to high efficiency Si solar cells and as a consequence high efficiencies were achieved. However, the development of high efficiency Si solar cells stagnated in the last years. In microelectronics Si nanocrystals (NCs) have been a subject of research for more than 15 years. Periodically aligned Si NCs in a dielectric matrix are a promising material for the application as an upper cell of a Si based tandem solar cell to realize very high efficiency solar cells. Recent modelling showed that a high density of Si nanocrystals within a SiC matrix has the highest potential, compared to SiO 2 or Si 3 N 4 , as a Si quantum dot absorber material [1]. To fabricate a Si quantum dot material by Plasma enhanced Chemical Vapour Deposition (PECVD) two different methods can be used: On the one hand a single layer approach, where the size of Si NCs is only controlled by the annealing conditions or a multilayer approach as proposed by Zacharias aiming at the control of the Si NCs by a stoichiometric diffusion barrier . The emphasis in this paper is placed on the single layer approach.
Materials
In this paper, the analysis, synthesis and characterization of thin films of a-Si:H deposited by PECVD were carried out. Three types of films were deposited: In the first series (00 process), an intrinsic a-Si:H film was doped. In the second series (A1–A5 process), n-type samples were doped, and to carry this out, a gas mixture of silane (SiH4), dihydrogen (H2) and phosphine (PH3) was used. In the third series (B1–B5 process), p-type samples were doped using a mixture of silane (SiH4), dihydrogen (H2) and diborane (B2H6). The films’ surface morphology was characterized by atomic force microscopy (AFM), while the analysis of the films was performed by scanning electron microscopy (SEM), and UV–visible ellipsometry was used to obtain the optical band gap and film thickness. According to the results of the present study, it can be concluded that the best conditions can be obtained when the flow of dopant gases (phosphine or diborane) increases, as seen in the conductivity graphs, where...
Thin Solid Films, 2017
The fabrication of crystalline silicon thin films on foreign substrates is an attractive and alternative approach to the ingot casting aiming to the reduction of the total costs of photovoltaic cells and modules. The purpose of this work is to describe the CRYSTALSI process which aims at forming polycrystalline silicon films thanks to the thermal crystallization of amorphous silicon layer deposited on aluminium based substrates. The latest are used as a catalyzer for silicon crystallization but also as a back metal contact and reflector for photovoltaic solar cells. Two types of aluminium substrates were applied in these studies: a pure aluminium substrate (99.7% purity) and a silicon rich aluminium substrate containing about 12% of silicon. Silicon thicknesses between 1 and 10 μm were deposited and then annealed at temperatures of 490°C, 520°C and 550°C and for duration times from 5 min to 12 h. The crystallized silicon films were then characterized by Raman spectroscopy, by scanning electron microscopy and by electron backscatter diffraction. The analyses show that the resulting annealed film is composed of two distinct layers: a thin polycrystalline silicon film located just above the substrate and a thicker layer made of a mixture of silicon and aluminium. Contrary to the case of the pure aluminium substrate, the silicon rich aluminium substrate allow to obtain thick and continuous polycrystalline silicon layers due to a controlled diffusion of the silicon within the substrate. As a result, the crystallization at 550°C of 5 μm thick amorphous silicon on silicon rich aluminium substrate led to the formation of a thick polycrystalline silicon layer composed of grains of few micrometers in size. A low activation energy of about 2 eV is extracted suggesting that the silicon rich aluminium substrate is a catalyzer for the crystallization of amorphous silicon. As for the AIC process, it can be noticed that the limiting step of the CRYSTALSI process is the diffusion of the silicon in the aluminium. A chemical etching using a HNO 3 , HF, H 2 O (72.5 ml/1.5 ml/28 ml) solution is found to be appropriate to remove the residual top layer, in order to have access to the polycrystalline silicon layer. This work demonstrates that the CRYSTALSI process can lead to the formation of polysilicon films that can serve as a seed layer for the growth of a thicker absorbing silicon film for photovoltaic applications.
Thin Solid Films, 2002
Plasma enhanced chemical vapour deposition (PECVD) is widely used to deposit materials on a variety of substrates at low temperature. However, examples of epitaxial growth on silicon with this technique are scarce. In this paper, we present homojunction silicon solar cells, epitaxially grown by PECVD, and mc-Siya-Si:Hyc-Si heterojunctions deposited with the same technique, manufactured by a completely low temperature process. All cells incorporate an intrinsic buffer layer, whose deposition conditions were varied. It is shown that the best V is obtained when the intrinsic layer is deposited under two extreme conditions, oc i.e. zero or very high (99.4%) hydrogen dilution of the gas mixture, resulting in a totally amorphous or epitaxial i-layer, respectively. Intermediate conditions result in V degradation. Efficiencies as high as 13.7% were obtained in planar devices that oc include an amorphous i-layer, and 13.1% in homojunction devices. ᮊ