Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Patent
1996-03-14
1998-09-22
Niebling, John
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
136255, 1566431, 1566621, H01L 3100
Patent
active
058109455
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an electronic device having the features indicated in the preamble of claim 1, the invention further relating to advantageous methods of fabricating such devices.
The operating behaviour of many electronic devices, such as solid-state or semiconductor devices including a solid-state or semiconductor system or some other controlled medium between two electrodes, particularly in the form of a film structure, is substantially influenced by how the electrodes are configured and patterned. One typical example are thin-film solar cells comprising a layer of amorphous silicon (a-Si). The problem forming the basis of the invention will be explained with reference to this preferred example application without being restricted thereto, however.
DESCRIPTION OF THE RELATED ART
As regards photocells, particularly solar cells, attaining a high efficiency in converting light energy into electrical energy whilst maintaining the production costs low and the life high is a problem which is still awaiting a satisfactory solution and which hitherto has prevented photovoltaic applications on a large scale. The most promising solution would appear to be at this time thin-film silicon solar cells having a p-i-n structure. Solar cells of this kind usually contain a so-called absorber layer of substantially inherently conducting amorphous silicon arranged between an n.sup.+ conducting doped and p.sup.+ conducting doped layer of amorphous silicon. This p-i-n film structure is normally arranged on a transparent substrate, a layer of a transparent electrically conductable material, usually of a metal oxide (TCO=Transparent Conducting Oxide) being disposed between the substrate and the film structure. Solar cells of a-Si require substantially less material than solar cells of single-crystal silicon (c-Si), since a-Si absorbs light in the visible spectral range substantially greater than c-Si, so that layer thicknesses of the order of a few hundred nanometers are sufficient with a-Si solar cells, whilst for solar cells of c-Si, layer thicknesses of the order of 100 to 300 .mu.m are necessary to achieve an adequate absorption of light in the visible spectral range. In addition, layers of a-Si are lighter in weight and require less complicated fabrication than single-crystal slices of silicon as required for c-Si solar cells.
One major drawback of a-Si as compared to c-Si is, however, the low mobility of the minority charge carriers (defect electrons). Even with the thin layer thicknesses, as are typical for a-Si solar cells, the majority of the photogenerated charge carriers recombine before they reach the electrode comprising the p.sup.+ conducting layer. The recombination energy destroys Si--Si bonds in the absorber layer which in the case of strong light irradiation results in a substantial reduction in efficiency (light-induced degradation; Staebler/Wronski effect) in relatively short time.
To minimize this light-induced degradation the thickness of the absorber layer (consisting substantially of inherently conducting a-Si and thus the necessary charge carrier drift lengths) was reduced. To nevertheless ensure adequate absorption of the incident light, the surface of the p-i-n film structure opposite that of light incidence was mirrored and the interface between the TCO layer of the electrically conducting oxide and the bordering silicon layer was patterned so that the incident light is refracted and/or dispersed at this interface. However, despite these measures the light-induced degradation caused by the recombination of minority charge carriers is still too high for practical applications of solar cells.
Similar problems rooted in small minority carrier drift lengths or in the electrode structure are experienced also in other solid-state or semiconductor devices such as electroluminescent devices, semiconductor devices emulating neuronal networks, as well as in LCD displays and many more such devices.
SUMMARY OF THE INVENTION
On the basis of this prior art the present
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Heintze Moritz
Nebel Christoph E.
Santos Paulo V.
Stutzmann Martin
Max-Planck-Gesellschaft zur Forderung der Wissenschaften e.v.
Niebling John
Turner Kevin F.
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