Thin layer p-n type heterojunction solar cells

Details Thin layer p-n type heterojunction solar cells Thin layer p-n type heterojunction solar cells

H - Electricity

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H01L 31/06 (2006.01) H01L 31/032 (2006.01) H01L 31/0336 (2006.01) H01L 31/072 (2006.01) H01L 31/18 (2006.01)

Patent

CA 1185347

ABSTRACT An improved light-to-electrical energy transducer such as a solar cell and, especially, a thin-film heterojunction solar cell formed of mate- rials selected from the class of I-III-VI2 chalco- pyrite compounds, and methods and apparatus for forming such thin-film cells, wherein the resulting cell is characterized by its relatively high energy conversion efficiency--viz., efficiencies closely ap- proximating on the order of 10%, or greater--and stability; yet, wherein the cell can be formed by thin-film, low cost, evaporation techniques on large area, low cost substrates. More particularly, an improved thin-film, large area solar cell, and meth- ods and apparatus for forming the same, having a relatively high light-to-electrical energy conversion efficiency and characterized in that the cell compri- ses a p-n-type heterojunction formed of: i) a first semiconductor layer comprising a photovoltaic active material selected from the class of I-III-VI2 chalco- pyrite ternary materials which is vacuum deposited in a thin "composition-graded" layer ranging from on the order of about 2.5 microns to about 5.0 microns (?-2.5µm to ?-5.0µm) and wherein the lower region of the photovoltaic active material preferably comprises a low resistivity region of p-type semiconductor material having a superimposed region of relatively high resistivity, transient n-type semiconductor material defining a transient p-n homojunction; and ii), a second semiconductor layer comprising a low resistivity n-type semiconductor material; wherein interdiffusion a) between the elemental constituents of the two discrete juxtaposed regions of the first semiconductor layer defining a transient p-n homo- junction layer, and b) between the transient n-type material in the first semiconductor layer and the second n-type semiconductor layer, causes the tran- sient n-type material in the first semiconductor layer to evolve into p-type material, thereby defin- ing a thin layer heterojunction device characterized by the absence of voids, vacancies and nodules which tend to reduce the energy conversion efficiency of the system. In the illustrative form of the invention described, the first semiconductor layer is prefer- ably formed of a first region of low resistivity p-type chalcopyrite material such, for example, as copper-enriched CuInSe2 to which is applied a tran- sient high resistivity n-type region of copper-defi- cient CuInSe2, while the second semiconductor layer preferably comprises an indium-doped CdS n-type layer.

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