Hybrid window layer for photovoltaic cells
A novel photovoltaic solar cell and method of making the same are disclosed. The solar cell includes: at least one absorber layer which could either be a lightly doped layer or an undoped layer, and at least a doped window-layers which comprise at least two sub-window-layers. The first sub-window-layer, which is next to the absorber-layer, is deposited to form desirable junction with the absorber-layer. The second sub-window-layer, which is next to the first sub-window-layer, but not in direct contact with the absorber-layer, is deposited in order to have transmission higher than the first-sub-window-layer.
1. A method for manufacturing a solar cell comprising the steps of:
(i) providing a substrate;
(ii) depositing a layer of n-type semi-conductor on the substrate at a temperature that is one of 300° C. and sufficiently low to avoid damage or melting the substrate;
(iii) depositing an i-layer on the n-layer at a temperature that is one of 300° C. and sufficiently low to avoid melting or damaging the n-layer;
(iv) depositing a first sub-p-layer on the i-layer at a first temperature sufficiently high to form a good junction with the i-layer; and
(v) depositing a second sub-p-layer on the first sub-p-layer at a temperature lower than the first temperature at which the first sub-p-layer is deposited.
2. The method of claim 1 , further including depositing a layer of a transparent conductive oxide on the second p-layer.
3. The method of claim 2 , wherein a current collection layer is deposited onto the substrate prior to deposition of the n-layer onto the substrate.
4. The method of claim 1 , wherein during the i-layer deposition an optimized GeH 4 to Si 2 H 6 ratio provides a Ge content suitable for forming a high efficiency single-junction solar cell.
5. The method of claim 4 , wherein an optimized level of hydrogen dilution is used to form the i-layer.
6. The method of claim 5 , wherein the substrate comprises glass or metal including aluminum, bismuth, iron, niobium, titanium or steel.
7. The method of claim 1 , wherein the first and second sub-p-layers are deposited by a chemical vapor deposition process.
8. The method of claim 7 , wherein the chemical vapor deposition process comprises plasma enhanced chemical vapor deposition.
9. The method of claim 8 , in which the plasma enhanced chemical vapor deposition comprises radio frequency plasma enhanced chemical vapor deposition.
10. The method of claim 9 , wherein the first and second p-layers amorphous silicon-containing material selected from the group consisting of hydrogenated amorphous silicon, hydrogenated amorphous carbon, and hydrogenated amorphous silicon germanium.
11. The method of claim 10 , wherein the i-layer comprises hydrogenated amorphous silicon germanium having a bandgap ranging from about 1.4 e-V to 1.6 e-V and wherein the first and second sub p-layers comprise amorphous silicon with a bandgap of 1.4 e-V.
12. The method of claim 11 , wherein the plasma enhanced chemical vapor deposition is by at least one of the following: cathodic direct current glow discharge, anodic direct current glow discharge, radio frequency glow discharge, very high frequency (VHF) glow discharge, alternate current glow discharge, or microwave glow discharge at a pressure ranging from about 0.5 to about 5 TORR with a dilution ratio of dilutant to feedstock (deposition gas) ranging from about 5:1 to about 200:1.