METHOD FOR HYDROGEN PLASMA TREATMENT OF A TRANSPARENT CONDUCTIVE OXIDE (TCO) LAYER

1 . A method for fabricating a thin film solar device, comprising:

providing a substrate having a transparent conductive oxide (TCO) layer deposited on a surface of the substrate, said TCO layer having an as deposited sheet resistance; and

exposing at least a portion of a surface of said TCO layer to a hydrogen plasma under conditions which result in a treated TCO layer having a reduced sheet resistance which is at least 10% less than the as deposited sheet resistance.

2 . The method of claim 1 , wherein said providing comprises depositing a ZnO layer on the surface of said substrate.

3 . The method of claim 1 , further comprising depositing a silicon layer on the treated TCO layer.

4 . The method of claim 2 , wherein said exposing comprises exposing the ZnO layer to said hydrogen plasma for a time duration ranging from about 2 minutes to about 20 minutes.

5 . The method of claim 4 , wherein said time duration ranges from about 2 minutes to about 10 minutes.

6 . The method of claim 5 , wherein said time duration ranges from about 2 minutes to about 5 minutes.

7 . The method of claim 2 wherein said exposing comprises exposing under a pressure condition of about 2 mBar.

8 . The method of claim 2 , wherein said exposing comprises exposing the ZnO layer under a power condition of 400 W RF power at 40.68 MHz.

9 . The method of claim 8 , wherein said exposing comprises exposing the ZnO layer under a condition of 200° C. substrate temperature.

10 . The method of claim 2 , wherein said exposing comprises exposing the ZnO layer under a condition of an H 2 flow rate of about 1800 sccm.

11 . The method of claim 2 , wherein said exposing results in the treated ZnO layer having a reduced sheet resistance of from 10 to 15 ohms square.

12 . The method of claim 2 , wherein:

said depositing comprises depositing a ZnO layer having an as deposited sheet resistance of from 12 to 54 ohms square; and

said exposing results in a treated ZnO layer having a reduced sheet resistance of from 10 to 15 ohms square.

13 . The method of claim 2 , further comprising controlling an exposure time of the ZnO layer based on an observed continuous increase in free electron mobility with increased H 2 plasma treatment time.

14 . The method of claim 2 , further comprising controlling an exposure time of the ZnO layer based on an observed continuous increase in free carrier density with increased H 2 plasma treatment time.

15 . The method of claim 2 , wherein said conditions include pressure, plasma power, and substrate temperature, the method further comprising varying at least one of said conditions to increase infrared reflectance of said ZnO layer to a higher wavenumber.

16 . The method of claim 2 , further comprising forming an amorphous silicon solar cell on said treated the ZnO layer, the amorphous silicon cell including a p-doped amorphous silicon layer and not including a p-doped microcrystalline silicon layer.

17 . The method of claim 16 , wherein said exposing enhances the properties of the amorphous silicon solar cell such that there is an increase of voltage open-circuit (V oc ) when compared to an amorphous silicon cell that did not undergo said exposing.

18 . The method of claim 18 , wherein the increase of V oc is an increase of from 10 to 20 mV over a V oc of the amorphous silicon solar cell that did not undergo said exposing.

19 . The method of claim 16 , wherein said amorphous silicon solar cell comprising two or more p-i-n junctions.

20 . The method of claim 2 , wherein said exposing substantially improves damp heat stability of the ZnO.