Showing papers by "Nicolas Wyrsch published in 1998"

Structural Properties and Electronic Transport in Intrinsic Microcrystalline Silicon Deposited by the VHF-GD Technique

Abstract: A series of microcrystalline samples was deposited by the very high frequency glow discharge (VHF-GD) technique, with various input powers while keeping all the other parameters of deposition constant. The goal was to correlate transport and structural properties and avoid as much as possible the problem of a variation of the Fermi level between the samples. The observed decrease of the photoconductivity and of the product mobility-lifetime of hole (as measured by time of flight, TOF) with the increase of the power was surprisingly not connected to the structural properties, which remain approximately unchanged, but with a surface contribution to the transport properties.

On the Transport Properties of Microcrystalline Silicon

Abstract: To determine the charge collection mechanism in hydrogenated microcrystalline silicon mc-Si:H solar cells, we have measured the electronic transport properties of mc-Si:H by time-of-flight and by ac capacitance and conductance on a unique 5.6 mm thick sample. We found the electron drift mobility m s 2.8 " 0.2 cm 2 V y1 s y1 , thermally activated with D E s 0.14 " 0.1 eV. Evidence for field inhomogeneity was observed as an initial maximum of the photocurrent transients A and as an increase of capacitance over the geometrical value. The frequency dependence of the capacitance exhibits marked differences from a-Si:H and is proposed as a tool for studying the effects of microstructure on electronic properties. Changes of the sample capacitance with temperature and illumination were observed. As a consequence of the inhomogeneity of the material, several different activation energies were found: 0.14 eV for electron drift mobility, 0.29 eV for ac conductivity, 0.4 eV for steady state dark conductivity and finally G 0.8 eV for the photocapacitance relaxation.

Stability of a-Si:H prepared by hot-wire and glow discharge using H2 dilution evaluated by pulsed laser degradation

Abstract: The quality of intrinsic amorphous silicon films prepared by different deposition techniques was investigated. For very high frequency glow discharge, both the substrate temperature as well as the hydrogen dilution were varied. These layers were compared to hot wire material produced at comparable temperatures. To study the stability of these films, an optimised degradation method was developed in which a pulsed dye laser was used in combination with a monochromatic steady beam to achieve a relatively fast stabilisation of the light induced degradation. The film quality was monitored by the photoconductivity and by the ambipolar diffusion length from which the material parameter, μ 0 τ 0 , was extracted. Taking into account the transport properties after light soaking as well as the optical absorption we concluded that the hot wire material could lead to more stable solar cells in comparison with plasma enhanced chemical vapor deposition material.

Microcrystalline p-i-n Cells: a Drift Controlled Device?

Abstract: The objective of this paper is to get more insight into the physics of microcrystalline silicon based solar cell by studying electric field profiles, spectral responses and current–voltage characteristics. Based on a comparison with a-Si:H p–i–n and c-Si p–n diodes, we concluded that μc-Si:H p–i–n devices are not field-controlled despite the presence of a high electric field in the i-layer.

Development of Inverted Micromorph Solar Cells

Abstract: I nstit ut f ur S chi t- d o eechn k , F rung ze m J liD-52425 G ma yABSTRACT: This paper gives a comprehensive overview of the development of the amorphous silicon/microcrystalline silicon "Micromorph" tandem cell deposited in the inverted configuration (n-i-p/n-i-p). Theobjective of this work is to achieve a high stable efficiency (> 10 %) with an innovative cell structure, to becompatible with various types of substrates (including non-transparent or flexible substrates), while taking intoaccount, at the same time, cost and ecological factors. In this context, ZnO conductive layers have beenintroduced as a replacement for ITO (Indium Tin Oxide) for both the top contact and the conducting backreflector. In a further important step towards potential cost reduction, high deposition rate of the bottommicrocrystalline silicon cell has been thoroughly investigated. First results on complete structures show initialefficiencies up to 9.3 % on glass, aluminium and stainless steel substrates.Keywords: Microcrystalline Si - 1; a-Si - 2; Multijunction Solar Cell - 3.1. INTRODUCTIONRecent progress has demonstrated that microcrystallinehydrogenated silicon (µc-Si:H) is a very attractive materialfor the active layer of thin film solar cells. Efficiencies ofup to 8.5 % have been achieved on entirelymicrocrystalline single p-i-n cells with no sign of light-induced degradation [1, 2]. By combining this cell with anamorphous silicon (a-Si:H)-based top cell and creatingthereby a tandem structure (the so-called "micromorph"cell), efficiencies in excess of 11 % (10.7 % confirmed)have been achieved [3, 4]. These results have resulted in arenewed interest for thin film crystalline silicon cells (e.g.see [5, 6].The "micromorph" structure has certain importantassets when implementing high efficiency and low costmodules: High efficiency potential with the combination of ahigh gap top cell (a-Si:H) and a low gap bottom one(

Charge Transport in Microcrystalline Silicon, Relation to Thin Film Solar Cells

Abstract: Note: IMT-NE Number: 281 Reference PV-LAB-CONF-1998-001 Record created on 2009-02-10, modified on 2017-05-10

Electric Field Profile in Jic-Si:H P-I-N Devices

Abstract: Solar cells based on microcrystalline silicon (ptc-Si:H) have demonstrated remarkable efficiencies and have been successfully incorporated in tandem structures; however, little work has so far been devoted to the understanding of these devices. The objective of this paper is to obtain more insight into their physical functioning by extensive characterisation of μc-Si:H devices. Charge-collection experiments shows that high electric field E(x) is present throughout the entire i-layer of thick p-i-n device. Furthermore, from capacitance studies, one concludes that the electric field profile is partly concentrated at grain boundaries. In contrast with these two observations, spectral response under forward bias voltage show that thick [tc-Si:H p-i-n devices are (unlike a-Si:H p-i-n devices) not fully field-controlled.