Embedded junction in hetero-structured back-surface field for photovoltaic devices
A photovoltaic device and method include a crystalline substrate and an emitter contact portion formed in contact with the substrate. A back-surface-field junction includes a homogeneous junction layer formed in contact with the crystalline substrate and having a same conductivity type and a higher active doping density than that of the substrate. The homogeneous junction layer includes a thickness less than a diffusion length of minority carriers in the homogeneous junction layer. A passivation layer is formed in contact with the homogeneous junction layer opposite the substrate, which is either undoped or has the same conductivity type as that of the substrate.
1. A photovoltaic device, comprising:
a crystalline substrate;
an emitter contact portion consisting of an intrinsic layer and a doped layer formed directly adjacent to each other, the intrinsic layer in direct contact with the substrate and the doped layer in direct contact with a first transparent conductive layer; and
a back-surface-field junction including:
a planar and continuous homogeneous junction layer in contact with an entirety of a rear surface of the crystalline substrate having a same conductivity type and a higher active doping density than that of the substrate, wherein the homogeneous junction layer includes a thickness less than a diffusion length of minority carriers in the homogeneous junction layer; and
a first surface of a passivation layer formed in contact with the homogeneous junction layer opposite the substrate, which is either doped or undoped, and a second surface of the passivation layer formed in direct contact with a second transparent conductive layer.
2. The photovoltaic device of claim 1 , wherein the homogeneous junction layer includes hydrogenated single-crystalline or poly-crystalline material.
3. The photovoltaic device of claim 2 , wherein the hydrogenated single-crystalline or poly-crystalline material includes Si having between 5 and 40 atomic percent hydrogen.
4. The photovoltaic device of claim 1 , wherein the passivation layer includes hydrogenated amorphous, nano-crystalline or micro-crystalline material including a same element as the homogeneous junction layer.
5. The photovoltaic device of claim 4 , wherein the same element is Si.
6. The photovoltaic device of claim 1 , wherein the homogeneous junction layer has an active doping density in a range of between about 10 18 and about 3×10 20 cm 3 .
7. The photovoltaic device of claim 1 , wherein the homogeneous junction layer includes a thickness in the range of between about 1 to about 25 nm.
8. The photovoltaic device of claim 1 , wherein the passivation layer has a thickness in a range of between about 2 and about 20 nm.
9. The photovoltaic device of claim 1 , wherein the substrate, the homogeneous junction layer, and the passivation layer include a same conductivity type.
10. The photovoltaic device of claim 1 , wherein the crystalline substrate includes a mono-crystalline or multi-crystalline substrate.
11. A photovoltaic device, comprising:
a substrate comprised of mono-crystalline or multi-crystalline material;
an emitter contact portion consisting of an intrinsic layer and a doped layer formed directly adjacent to each other, the intrinsic layer in direct contact with the substrate and the doped layer in direct contact with a first transparent conductive layer; and
a back-surface-field junction including:
a planar and continuous homogeneous junction layer in contact with an entirety of a rear surface of the substrate, the homogeneous junction layer including a hydrogenated single-crystalline or poly-crystalline material having a same conductivity type and a higher active doping density than that of the substrate, wherein the homogeneous junction layer includes a thickness less than a diffusion length of minority carriers in the homogeneous junction layer, wherein the diffusion length of the minority carriers ranges from 50 nm to 2 microns;
a first surface of a passivation layer formed in contact with the homogeneous junction layer opposite the substrate, which is either doped or undoped, and a second surface of the passivation layer formed in direct contact with a second transparent conductive layer; and
a conductive contact portion.
12. The photovoltaic device of claim 11 , wherein the homogeneous junction layer includes between 5 and 40 atomic percent hydrogen.
13. The photovoltaic device of claim 11 , wherein the hydrogenated single-crystalline or poly-crystalline material includes Si.
14. The photovoltaic device of claim 11 , wherein the passivation layer includes hydrogenated non-crystalline material including a same element as the homogeneous junction layer.
15. The photovoltaic device of claim 14 , wherein the hydrogenated non-crystalline material includes hydrogenated amorphous Si.
16. The photovoltaic device of claim 11 , wherein the homogeneous junction layer has an active doping density in a range of between about 10 18 and about 3×10 20 cm 3 .
17. The photovoltaic device of claim 11 , wherein the homogeneous junction layer includes a thickness in the range of between about 1 to about 25 nm.
18. The photovoltaic device of claim 11 , wherein the passivation layer has a thickness in a range of between about 2 and about 20 nm.