APPARATUS AND METHOD FOR PRODUCING CIGS ABSORBER LAYER IN SOLAR CELLS

1 . A method of forming an absorber layer of a solar cell, comprising:

forming a plurality of precursor layers over a surface of a bottom electrode of a solar cell substrate, the step of forming comprising:

depositing a first layer comprising selenium and copper over at least a portion of the surface using a sputtering source or an evaporation source, the first layer having a first concentration of copper;

depositing a second layer comprising selenium and at least two of the group consisting of copper, gallium or indium over at least the portion of the surface, the second layer having a second concentration of copper less than the first concentration of copper; and

annealing the precursor layers to form an absorber layer.

2 . The method of claim 1 , further comprising:

depositing a buffer layer over the absorber layer using another sputtering source.

3 . The method of claim 1 , wherein the absorber layer has a copper gallium indium ratio, calculated as copper mole/(gallium mole+indium mole), in a range about 0.85 to about 0.95.

4 . The method of claim 3 , wherein the second layer comprises at least one of the combinations of:

copper, indium, gallium and selenium or

copper, gallium and selenium or

indium, gallium and selenium.

5 . (canceled)

6 . (canceled)

7 . The method of claim 4 , further comprising depositing a third layer after the first layer or the second layer, the third layer comprising selenium and copper and at least one of gallium or indium.

8 . The method of claim 7 , further comprising depositing a layer of selenium over the second layer.

9 . The method of claim 1 , wherein the steps of depositing the first layer and the second layer comprise sputtering at least two of copper-gallium, indium or copper, and evaporating gallium and selenium.

10 . (canceled)

11 . The method of claim 1 , wherein the steps of depositing are performed by:

providing a solar cell forming apparatus comprising a housing defining a vacuum chamber, a rotatable substrate apparatus within the housing for holding a substrate, and a copper source, an indium source, a gallium source, and a selenium source disposed within the vacuum chamber between the rotatable substrate apparatus and housing;

positioning the substrate on the rotatable substrate apparatus; and

rotating the rotatable substrate apparatus while providing material from a first combination of the sources, including the selenium source and the copper source then providing material from a second combination of the sources, including at least two of the group consisting of the copper source, the indium source and gallium source to deposit the second layer.

12 . The method of claim 3 , wherein the first layer has a copper gallium indium ratio of at least 1.0.

13 . The method of claim 4 , wherein the second layer has a copper gallium indium ratio below 0.7.

14 . (canceled)

15 . (canceled)

16 . A method of forming an absorber layer of a solar cell, comprising:

forming a plurality of precursor layers over a surface of a bottom electrode of a solar cell substrate, the step of forming comprising:

depositing a first layer comprising selenium and at least one of gallium or indium over at least a portion of the surface using a sputtering source or an evaporation source;

depositing a second layer comprising selenium and copper over at least the portion of the surface, the second layer having a second concentration of copper;

depositing a third layer comprising selenium and at least two of the group consisting of copper, gallium or indium over at least the portion of the surface, the third layer having a third concentration of copper less than the second concentration of copper; and

annealing the precursor layers to form an absorber layer.

17 . The method of claim 16 , wherein the first layer comprises selenium, gallium, and indium, the second layer comprises copper and selenium, and the third layer comprises selenium, gallium, and indium.

18 . (canceled)

19 . (canceled)

20 . The method of claim 16 , wherein the absorber layer has a copper gallium indium ratio,, calculated as copper mole/(gallium mole+indium mole), in a range about 0.85 to about 0.95.

21 . The method of claim 16 , wherein the third layer comprises copper.

22 . The method of claim 16 , wherein the third layer comprises gallium and indium.

23 . A method of forming a precursor layer stack on a substrate of a solar cell for forming an absorber layer, comprising:

providing a solar cell forming apparatus comprising a housing defining a vacuum chamber, a rotatable substrate apparatus within the housing for holding the substrate, and a plurality of sources disposed within the vacuum chamber between the rotatable substrate apparatus and housing, wherein the plurality of sources include a copper source, an indium source, a gallium source, and a selenium source;

rotating a solar cell substrate on the rotatable substrate apparatus while depositing from the plurality of sources a first layer comprising selenium and copper over at least a portion of a surface of a bottom electrode of the solar cell substrate, the first layer having a first concentration of copper; and

rotating a solar cell substrate on the rotatable substrate apparatus while depositing from the plurality of sources a second layer comprising selenium and at least two of the group consisting of copper, gallium or indium over at least the portion of the surface, the second layer having a second concentration of copper less than the first concentration of copper.

24 . The method of claim 23 , wherein said depositing steps are performed by, in order:

turning on the copper and selenium sources to deposit the first layer; and

turning off the copper source, turning on the indium and gallium sources, and keeping the selenium source on to deposit the second layer.

25 . The method of claim 23 , further comprising depositing a third layer comprising selenium, gallium and indium over at least the portion of the surface before depositing the first and second layers , wherein said depositing steps are performed by, in order:

turning on the indium, gallium and selenium sources to deposit the third layer;

turning off the indium and gallium sources, turning on the copper source, and keeping the selenium source on to deposit the first layer; and

turning off the copper source and turning on the indium and gallium sources to deposit the second layer.

26 . The method of claim 23 , wherein the copper and indium sources comprise sputtering sources and the selenium and gallium sources comprise evaporation sources.

27 . The method of claim 26 , wherein the plurality of sources further comprise a copper-gallium sputtering source.