Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Patent
1996-03-26
1997-10-14
Weisstuch, Aaron
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
H01C 3106
Patent
active
056767668
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
A main objective in photovoltaics is the development of solar cells with the best possible long-term stability and high efficiency, with simultaneously low production costs. Only then will this form of energy production be competitive with other conventional methods.
As regards efficiency and long-term stability, solar modules of monocrystalline silicon are presently considered as standard. Because of high production costs and long energy return times, i.e. periods over which the energy used in production is compensated for by photovoltaic power generation, solar power from such standard modules has not yet reached the threshold of competitiveness.
Solar cells of polycrystalline I-III-VI.sub.2 chalcopyrite semiconductors are presently expected to make promising contributions in the production of cost-efficient and long-term stable solar cells. In particular, CuInSe.sub.2 (CIS) and related alloys are materials which have a high absorption coefficient, a direct band transition and a band gap that is matched to the solar spectrum. They can be produced using cost-effective thin-film deposition methods and have already reached efficiencies of almost 17% in laboratory tests.
A cell structure disclosed by U.S. Pat. No. 5,141,564 consists of a glass substrate, a molybdenum back electrode, a 1 to 5 .mu.m thick absorber layer of polycrystalline chalcopyrite semiconductor of composition CuInGaSe.sub.2 or CuIn(S,Se).sub.2, a thin cadmium sulfide window layer and a transparent front electrode.
Until now, disadvantages with CIS solar cells have been the poor adhesion of the absorber layer on the molybdenum back electrode and the poor reproducibility, the basis of which is the complex production process for ternary semiconductors.
For production, the components are applied over the substrate in elemental form, either one after the other or together, and are made to react with one another by establishing suitable reaction conditions (2-stage process). It is also possible to apply only the two metallic components and to prepare the nonmetallic reaction partner using a correspondingly reactive atmosphere. A further possibility consists in vapor-depositing the starting components in elemental form onto a preheated substrate, the reaction to form the ternary semiconductor taking place directly before or after the components reach the substrate. This one-stage process is, however, difficult to carry out as a full-surface deposition process, since layer uniformity cannot be ensured with relatively large areas.
Particularly in the case of the two-stage process, detachment of the absorber layer from the molybdenum back electrode is observed and in the production of solar cells this directly leads to a batch of nonfunctioning or reduced-power solar cells. Further damage due to layer detachment can be observed during subsequent operation of the solar cells, as a result of differential thermal loading between daytime and nighttime or when the seasons change.
U.S. Pat. No. 4,915,745 discloses the use of a Ga intermediate layer as an adhesive between a molybdenum back electrode and a CIS layer. Although the adhesion of the absorber layer on the back electrode is thereby improved, the homogeneity of the layers is nevertheless simultaneously reduced.
International application WO 90/15 445 A 1 discloses a tellurium intermediate layer, the purpose of which is for the adhesion between the molybdenum back electrode and the absorber layer to be improved. A disadvantage with this method is, as with U.S. Pat. No. 4,915,745 mentioned above, the introduction of a new and, in the case of tellurium, also toxic material into the layer structure of the CIS solar cell. This increases the complexity of the depositions and therefore the expenditure in production. In addition, problems arise in the disposal of solar cells that are no longer capable of functioning.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide a solar cell that has improved adhesion between the substrate and the absor
REFERENCES:
patent: 4536607 (1985-08-01), Wiesmann
patent: 4642140 (1987-02-01), Noufi et al.
patent: 4915745 (1990-04-01), Pollock et al.
patent: 5141564 (1992-08-01), Chen et al.
Solar Energy Materials, vol. 23, No. 1, Nov. 1991, C. Guillen et al, "Optical properties of electrochemically deposited CuInSe/2 thin films", pp. 31-45.
Karg Franz
Probst Volker
Siemens Aktiengesellschaft
Weisstuch Aaron
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