Physical metallurgy of Ti–Ni-based shape memory alloys

TCO and light trapping in silicon thin film solar cells

Solar photovoltaic electricity: Current status and future prospects

This paper describes the use, within p–i–n- and n–i–p-type solar cells, of hydrogenated amorphous silicon (a-Si:H) and hydrogenated microcrystalline silicon (μc-Si:H) thin films (layers), both deposited at low temperatures (200°C) by plasma-assisted chemical vapour deposition (PECVD), from a mixture of silane and hydrogen. Optical and electrical properties of the i-layers are described. These properties are linked to the microstructure and hence to the i-layer deposition rate, that in turn, affects throughput in production. The importance of contact and reflection layers in achieving low electrical and optical losses is explained, particularly for the superstrate case. Especially the required properties for the transparent conductive oxide (TCO) need to be well balanced in order to provide, at the same time, for high electrical conductivity (preferably by high electron mobility), low optical absorption and surface texture (for low optical losses and pronounced light trapping). Single-junction amorphous and microcrystalline p–i–n-type solar cells, as fabricated so far, are compared in their key parameters (Jsc, FF, Voc) with the [theoretical] limiting values. Tandem and multijunction cells are introduced; the μc-Si: H/a-Si: H or [micromorph] tandem solar cell concept is explained in detail, and recent results obtained here are listed and commented. Factors governing the mass-production of thin-film silicon modules are determined both by inherent technical reasons, described in detail, and by economic considerations. The cumulative effect of these factors results in distinct efficiency reductions from values of record laboratory cells to statistical averages of production modules. Finally, applications of thin-film silicon PV modules, especially in building-integrated PV (BIPV) are shown. In this context, the energy yields of thin-film silicon modules emerge as a valuable gauge for module performance, and compare very favourably with those of other PV technologies. Copyright © 2004 John Wiley & Sons, Ltd.

Thin‐film silicon solar cell technology

Intrinsic microcrystalline silicon: A new material for photovoltaics

The growth of microcrystalline silicon prepared by plasma-enhanced chemical vapour deposition depends on the deposition conditions and yields films with variable content of crystalline grains, amorphous network, grain boundaries and voids. The changes in the structural properties of a series of films grown under a variation of the dilution of the process gas silane in hydrogen, which induces a transition from highly crystalline to amorphous growth, were investigated. The evolution of the crystalline volume fraction was quantitatively analysed by Raman spectroscopy and X-ray diffraction. The results confirm the need for proper correction of the Raman data for optical absorption and Raman cross-section. Transmission electron microscopy was used to investigate the characteristics and the variation in the microstructure. Upon increasing the silane concentration the strong columnar growth with narrow grain boundaries degrades towards the growth of small irregularly shaped grains enclosed in an amorpho...

Structural properties of microcrystalline silicon in the transition from highly crystalline to amorphous growth

The influence of the plasma excitation frequency on the growth conditions and the material properties of microcrystalline silicon prepared by plasma enhanced chemical vapor deposition at low deposition temperature is investigated. It is found that an increase of the plasma excitation frequency leads to a simultaneous increase of the growth rate, the grain size, and the Hall mobility of microcrystalline silicon. This is attributed to an effective selective etching of disordered material creating more space to develop crystalline grains, while also more species for faster growth of the crystallites are available.

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Improvement of grain size and deposition rate of microcrystalline silicon by use of very high frequency glow discharge

Microcrystalline silicon prepared by plasma-enhanced chemical vapour deposition consists of variable volume fractions of amorphous phase, grain boundaries, cavities and crystalline grains. In this paper the structural properties, which strongly depend on the growth conditions, were investigated in detail by transmission electron microscopy and by Raman spectroscopy. A columnar structure parallel to the growth direction is observed for all conditions investigated. By increasing the plasma excitation frequency the crystalline volume fraction and the grain sizes are enhanced. Simultaneously an increase in the growth rate can be achieved, which is accompanied by an increasing etch rate of amorphous material. In addition, spherical voids were found predominantly in samples prepared at a low plasma excitation frequency. The growth of a porous initial layer containing a high density of ‘crack-line’ voids is observed when high plasma excitation frequencies are applied. These results suggest that the micr...

Structure and growth of hydrogenated microcrystalline silicon : investigation by transmission electron microscopy and Raman spectroscopy of films grown at different plasma excitation frequencies

The initial growth stage of phosphorus doped microcrystalline silicon films prepared by plasma enhanced chemical vapor deposition with different plasma excitation frequencies in the range 13.56–116 MHz was studied by Raman and infrared spectroscopy, optical transmission and reflection, and conductivity measurements. The sensitivity of Raman spectroscopy and optical reflection on Si crystallites in the initial growth regime is compared and optical reflection at 4.5 eV is proposed as an easy and reliable tool for this investigation. While the crystallite formation on amorphous silicon substrates at 13.56 MHz is delayed in comparison with glass, SiO2 and chromium substrates, nucleation of the crystalline phase on amorphous silicon is found to be greatly enhanced at higher plasma excitation frequencies. On the other hand, for deposition on glass, SiO2, and chromium at frequencies equal to or higher than 70 MHz, increased porosity is found in the initial growth region. The results are interpreted within a mode...

P. Hapke

Papers

Intrinsic microcrystalline silicon: A new material for photovoltaics

Structural properties of microcrystalline silicon in the transition from highly crystalline to amorphous growth

Improvement of grain size and deposition rate of microcrystalline silicon by use of very high frequency glow discharge

Structure and growth of hydrogenated microcrystalline silicon : investigation by transmission electron microscopy and Raman spectroscopy of films grown at different plasma excitation frequencies

Optical and transport studies on thin microcrystalline silicon films prepared by very high frequency glow discharge for solar cell applications