ELECTROPLATING METHODS AND CHEMISTRIES FOR CIGS PRECURSOR STACKS WITH CONDUCTIVE SELENIDE BOTTOM LAYER
The present invention provides a method and precursor structure to form a solar cell absorber layer. The method includes forming a CIGS solar cell absorber on a base by depositing a first layer on the base, where in the first layer includes non-crystalline copper-selenide that is electrically nonconductive, and then heat treating the first layer at a first temperature range to transform the non-crystalline copper-selenide into a crystalline copper-selenide that is electrically conductive, thereby ensuring that the first layer becomes a first conductive layer. Thereafter, other steps follow to complete formation of the CIGS solar cell absorber.
1 . A method of forming a CIGS solar cell absorber on a base, comprising:
forming a precursor stack, comprising the steps of:
depositing a first layer on the base, wherein the first layer includes non-crystalline copper-selenide that is electrically nonconductive;
heat treating the first layer at a first temperature range to transform the non-crystalline copper-selenide into a crystalline copper-selenide that is electrically conductive, thereby ensuring that the first layer becomes a first conductive layer;
electrodepositing a second conductive layer onto the first conductive layer after the step of heat treating, wherein the second conductive layer includes at least one of copper, indium and gallium;
electrodepositing a third layer onto the second layer, the third layer including selenium;
depositing a fourth layer onto the third layer, the fourth layer including a dopant element and selenium; and
reacting the precursor stack to form the CIGS absorber layer on the base.
2 . The method of claim 1 , wherein the step of depositing the first layer includes electrodeposition.
3 . The method of claim 1 , wherein the crystalline copper selenide includes Cu 2−x Se, where x can range from 0 approximately up to 0.3.
4 . The method of claim 3 further comprising, after the step of heat treatment, the step of depositing a copper layer onto the first conductive layer including the crystalline copper selenide.
5 . The method of claim 4 , wherein the second conductive layer is a stack comprising a layer including gallium electrodeposited onto the first conductive layer and another layer including at least one of indium and an indium/copper stack electrodeposited onto the layer.
6 . The method of claim 4 , wherein the copper layer is electrodeposited from an electrolyte having a pH of less than 4 while applying a potential in the range of −0.2 to 0.4 with respect to standard hydrogen electrode.
7 . The method of claim 1 , wherein a Se/Cu atomic ratio of the non-crystalline copper selenide layer is about 1.
8 . The method of claim 1 , wherein a Se/Cu atomic ratio of the crystalline copper selenide layer is more than 1.
9 . The method of claim 1 , wherein the temperature range of the heat treatment is 350-600° C., and a duration of the heat treatment has a duration of in the range of 1 to 60 minutes.
10 . The method of claim 9 , wherein the heat treatment is performed in an oxygen free environment.
11 . The method of claim 1 , wherein the step of depositing the first layer includes sputter deposition.
12 . The method of claim 1 , wherein the step of depositing the first layer includes evaporation deposition.
13 . The method of claim 1 , wherein the step of depositing the fourth layer includes evaporation deposition.
14 . A method of forming a CIGS solar cell absorber on a base, comprising:
forming a precursor stack, comprising the steps of:
depositing a first layer on the base, wherein the first layer includes copper-selenide that is no more than partially conductive, such that the entire first layer is no more than partially conductive;
heat treating the first layer at a first temperature range to transform the copper-selenide into a crystalline copper-selenide that is electrically conductive, thereby ensuring that the first layer becomes a first conductive layer;
electrodepositing a second conductive layer onto the first conductive layer after the step of heat treating, wherein the second conductive layer includes at least one of copper, indium and gallium;
electrodepositing a third layer onto the second layer, the third layer including selenium;
depositing a fourth layer onto the third layer, the fourth layer including a dopant element and selenium; and
reacting the precursor stack to form the CIGS absorber layer on the base.
15 . The method of claim 14 , wherein the step of depositing the first layer includes electrodeposition.
16 . The method of claim 14 , wherein the crystalline copper selenide includes Cu 2−x Se, where x can range from 0 approximately up to 0.3.
17 . The method of claim 16 further comprising, after the step of heat treatment, the step of depositing a copper layer onto the first conductive layer including the crystalline copper selenide.
18 . The method of claim 17 , wherein the second conductive layer is a stack comprising a layer including gallium electrodeposited onto the first conductive layer and another layer including at least one of indium and an indium/copper stack electrodeposited onto the layer.
19 . The method of claim 17 , wherein the copper layer is electrodeposited from an electrolyte having a pH of less than 4 while applying a potential in the range of −0.2 to 0.4 with respect to standard hydrogen electrode.
20 . The method of claim 14 , wherein a Se/Cu atomic ratio of the copper selenide layer is about 1.
21 . The method of claim 14 , wherein a Se/Cu atomic ratio of the copper selenide layer is more than 1.
22 . The method of claim 14 , wherein the temperature range of the heat treatment is 350-600° C., and a duration of the heat treatment has a duration of a duration in the range of 1 to 60 minutes.
23 . The method of claim 22 , wherein the heat treatment is performed in an oxygen free environment.
24 . The method of claim 14 , wherein the step of depositing the first layer includes sputter deposition.
25 . The method of claim 14 , wherein the step of depositing the first layer includes evaporation deposition.
26 . The method of claim 14 , wherein the step of depositing the fourth layer includes evaporation deposition.