PASSIVATION OF LIGHT-RECEIVING SURFACES OF SOLAR CELLS WITH HIGH ENERGY GAP (EG) MATERIALS
Methods of passivating light-receiving surfaces of solar cells with high energy gap (Eg) materials, and the resulting solar cells, are described. In an example, a solar cell includes a substrate having a light-receiving surface. A passivating dielectric layer is disposed on the light-receiving surface of the substrate. A Group III-nitride material layer is disposed above the passivating dielectric layer. In another example, a solar cell includes a substrate having a light-receiving surface. A passivating dielectric layer is disposed on the light-receiving surface of the substrate. A large direct band gap material layer is disposed above the passivating dielectric layer, the large direct band gap material layer having an energy gap (Eg) of at least approximately 3.3. An anti-reflective coating (ARC) layer disposed on the large direct band gap material layer, the ARC layer comprising a material different from the large direct band gap material layer.
1 . A method of fabricating a solar cell, the method comprising:
forming a passivating dielectric layer on a light-receiving surface of a substrate;
forming a Group III-nitride material layer above the passivating dielectric layer; and
forming an anti-reflective coating (ARC) layer on the Group III-nitride material layer.
2 . The method of claim 1 , further comprising:
forming an interfacial layer on the passivating dielectric layer, wherein forming the Group III-nitride material layer comprises forming the Group III-nitride material layer on the interfacial layer.
3 . The method of claim 1 , wherein forming the Group III-nitride material layer comprises forming a polycrystalline layer selected from the group consisting of an aluminum nitride (AlN) polycrystalline layer, an aluminum gallium nitride (Al x Ga 1-x N, where 0<x<1) polycrystalline layer, and a gallium nitride (GaN) polycrystalline layer by a technique selected from the group consisting of metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and physical vapor deposition (PVD), or comprises forming an amorphous layer selected from the group consisting of an aluminum nitride (AlN) amorphous layer, an aluminum gallium nitride (Al x Ga 1-x N, where 0<x<1) amorphous layer, and a gallium nitride (GaN) amorphous layer by a technique selected from the group consisting of plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), plasma-enhanced atomic layer deposition (PEALD), molecular beam epitaxy (MBE), and physical vapor deposition (PVD).
4 . The method of claim 1 , wherein forming the Group III-nitride material layer comprises forming a polycrystalline layer selected from the group consisting of an aluminum nitride (AlN) polycrystalline layer, an aluminum gallium nitride (Al x Ga 1-x N, where 0<x<1) polycrystalline layer, and a gallium nitride (GaN) polycrystalline layer by a technique selected from the group consisting of metal-organic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), plasma-enhanced atomic layer deposition (PEALD), molecular beam epitaxy (MBE), and physical vapor deposition (PVD), or comprises forming an amorphous layer selected from the group consisting of an aluminum nitride (AlN) amorphous layer, an aluminum gallium nitride (Al x Ga 1-x N, where 0<x<1) amorphous layer, and a gallium nitride (GaN) amorphous layer by a technique selected from the group consisting of plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), plasma-enhanced atomic layer deposition (PEALD), molecular beam epitaxy (MBE), and physical vapor deposition (PVD).
5 . A method of fabricating a solar cell, the method comprising:
forming a passivating dielectric layer on a light-receiving surface of a substrate;
forming a Group III-nitride material layer above the passivating dielectric layer, wherein the Group III-nitride material layer comprises gallium; and
forming an interfacial layer directly between the passivating dielectric layer and the Group III-nitride material layer, the interfacial layer comprising a material different from the passivating dielectric layer and different from the Group III-nitride material layer, wherein the interfacial layer is a silicon-rich amorphous silicon layer and has a thickness approximately in the range of 30-50 Angstroms.
6 . The method of claim 5 , wherein the Group III-nitride material layer is disposed on the passivating dielectric layer.
7 . The method of claim 5 , wherein the Group III-nitride material layer is selected from the group consisting of an aluminum gallium nitride (Al x Ga 1-x N, where 0<x<1) layer, and a gallium nitride (GaN) layer.
8 . The method of claim 5 , further comprising:
forming an anti-reflective coating (ARC) layer on the Group III-nitride material layer, the ARC layer comprising a material different from the Group III-nitride material layer.
9 . The method of claim 8 , wherein the ARC layer is a layer selected from the group consisting of an aluminum oxide (AlO x , x is equal to or less than 1.5) layer and a silicon oxynitride (SiO y N z , y>0, z>0) layer, and wherein the ARC layer and the Group III-nitride material layer together form a dual layer anti-reflective coating for the solar cell.
10 . The method of claim 9 , wherein the Group III-nitride material layer has a thickness approximately in the range of 50-900 Angstroms and has an index of refraction of approximately 2.0-2.4, and wherein the ARC layer has a thickness approximately in the range of 300-1500 Angstroms and has an index of refraction of approximately 1.8.
11 . The method of claim 10 , wherein the Group III-nitride material layer and the ARC layer together provide current enhancement and stability for the solar cell.
12 . The method of claim 8 , wherein the ARC layer is a layer of hydrogenated silicon nitride (SiN:H).
13 . The solar cell of claim 11 , wherein the Group III-nitride material layer has a thickness approximately in the range of 30-100 Angstroms and has an index of refraction of approximately 2.0-2.4, and wherein the layer of SiN:H has a thickness of approximately 700 Angstroms and has an index of refraction greater than approximately 1.9.
14 . The method of claim 13 , wherein the Group III-nitride material layer and the ARC layer together provide stability for the solar cell while the high band Eg material provides passivation with no absorption of the photogenerating spectrum.
15 . The method of claim 5 , wherein the substrate is a crystalline silicon substrate, and the passivating dielectric layer is a layer of silicon dioxide (SiO 2 ) having a thickness approximately in the range of 10-300 Angstroms.
16 . The method of claim 5 , wherein the light-receiving surface has a texturized topography, and wherein both the passivating dielectric layer and the Group III-nitride material layer are conformal with the texturized topography of the light-receiving surface.
17 . The method of claim 5 , wherein the substrate further comprises a back surface opposite the light-receiving surface, the method further comprising:
forming a plurality of alternating N-type and P-type semiconductor regions at or above the back surface of the substrate; and
forming a conductive contact structure electrically connected to the plurality of alternating N-type and P-type semiconductor regions.
18 . A method of fabricating a solar cell, the method comprising:
forming a passivating dielectric layer on a light-receiving surface of a substrate;
forming an interfacial layer directly on the the passivating dielectric layer, the interfacial layer comprising a material different from the passivating dielectric layer, wherein the interfacial layer is a silicon-based layer with no oxygen, the layer selected from the group consisting of silicon-rich amorphous silicon, intrinsic or phosphorus doped amorphous silicon, and polycrystalline silicon, and wherein the silicon-based layer has a thickness approximately in the range 10-200 Angstroms; and
forming a Group III-nitride material layer directly on the interfacial layer, wherein the Group III-nitride material layer comprises gallium, and wherein the Group III-nitride material layer comprises a material different than the interfacial layer.
19 . The method of claim 18 , wherein the Group III-nitride material layer is selected from the group consisting of an aluminum gallium nitride (Al x Ga 1-x N, where 0<x<1) layer, and a gallium nitride (GaN) layer.
20 . The method of claim 18 , further comprising:
forming an anti-reflective coating (ARC) layer on the Group III-nitride material layer, the ARC layer comprising a material different from the Group III-nitride material layer.