Selective emitter solar cells formed by a hybrid diffusion and ion implantation process
Solar cells and methods for their manufacture are disclosed. An example solar cell may comprise a substrate comprising a p-type base layer and an n-type selective emitter layer formed over the p-type base layer. The n-type selective emitter layer may comprise one or more first doped regions comprising implanted dopant and one or more second doped regions comprising diffused dopant. The one or more first doped regions may be more heavily doped than the one or more second doped regions. A p-n junction may be formed at the interface of the base layer and the selective emitter layer, such that the p-n junction and the selective emitter layer are both formed during a single anneal cycle.
1. A solar cell comprising:
a substrate comprising a p-type base layer;
an n-type selective emitter layer disposed over the p-type base layer,
the n-type selective emitter layer comprising:
one or more first doped regions and one or more second doped regions, wherein the one or more first doped regions are more heavily doped than the one or more second doped regions, and wherein a resistance ratio between the one or more first doped regions and the one or more second doped regions is from about 0.25 to about 0.625; and
a p-n junction at the interface of the base layer and the selective emitter layer;
wherein the selective emitter is formed by the use of a hybrid diffusion and ion implantation process, wherein the one or more first dosed regions comprise an ion implanted dopant, wherein the ion implanted dopant comprises phosphorous, wherein the one or more second doped regions comprise a diffused dopant, wherein the diffused dopant is formed by introducing a dopant for diffusion in the form of phosphorous oxychloride (POCl 3 ), and wherein an additional dopant is diffused into a front surface of the base layer, creating misfit dislocations in the selective emitter layer to provide a sink for iron gettering; and injecting interstitials into the substrate to drive iron from substitutional sites into interstitial sites such that the iron diffuses rapidly to the gettering sink.
2. The solar cell of claim 1 , the n-type selective emitter layer comprising a front surface, and the solar cell further comprising an antireflection layer disposed on the front surface of the selective emitter layer.
3. The solar cell of claim 2 , the antireflection layer comprising a front surface, a base layer comprising a back surface, and the solar cell further comprising: one or more screen-printed front contacts disposed on the front surface of the antireflection layer in electrical communication with the selective emitter layer through the antireflection layer; and one or more screen-printed back contacts disposed on the back surface of the base layer.
4. The solar cell of claim 3 , further comprising: an aluminum-doped p + back surface field layer at the interface of the base layer and the one or more back contacts, wherein the one or more back contacts are in electrical communication with the aluminum-doped p + back surface field layer.
5. The solar cell of claim 3 , wherein the one or more front contacts are aligned with the more heavily doped one or more first doped regions of the selective emitter layer to reduce contact resistance, and wherein the one or more front contacts are in electrical communication with the one or more first doped regions of the selective emitter layer.
6. The solar cell of claim 1 , wherein the p-n junction and the selective emitter layer are both formed during a single anneal cycle.
7. A solar cell having a selective emitter formed by the use of a hybrid diffusion and ion implantation process, manufactured by the steps of: providing a substrate comprising a base layer, wherein the base layer is doped with p-type dopant; introducing dopant to one or more selective regions of the front surface of the base layer by ion implantation to form an ion implanted dopant; and annealing the substrate, wherein annealing comprises heating the substrate in a furnace to a temperature to: diffuse additional dopant into the front surface of the base layer, wherein the additional dopant is introduced to the furnace during the anneal to form a diffused dopant; and form a selective emitter layer on the front surface of the base layer, wherein the one or more selective regions of the front surface of the base layer define one or more selective regions of the selective emitter layer that are more heavily doped than the remainder of the selective emitter layer, and wherein a resistance ratio between the one or more selective regions of the selective emitter layer and the remainder of the selective emitter layer is from about 0.25 to about 0.625; wherein the selective emitter layer is doped with an n-type dopant such that a p-n junction forms at the interface of the base layer and the selective emitter layer; wherein the ion implanted dopant comprises phosphorous; wherein the diffused dopant is formed by introducing a dopant for diffusion in the form of phosphorous oxychloride (POCl 3 ), and wherein diffusing an additional dopant into the front surface of the base layer further comprises: creating misfit dislocations in the selective emitter layer to provide a sink for iron gettering: and injecting interstitials into the substrate to drive iron from substitutional sites into interstitial sites such that the iron diffuses rapidly to the gettering sink.
8. A solar cell comprising:
a substrate comprising an n-type base layer;
a p-type selective emitter layer formed over the n-type base layer, the p-type
selective emitter layer comprising:
one or more first doped regions and one or more second doped regions, wherein the one or more first doped regions are more heavily doped than the one or more second doped regions, and wherein a resistance ratio between the one or more first doped regions and the one or more second doped regions is from about 0.25 to about 0.625; and
a p-n junction at the interface of the base layer and the selective emitter layer;
wherein the selective emitter layer is formed by the use of a hybrid diffusion and ion implantation process, wherein the one or more first doped regions comprise an ion implanted dopant, wherein the ion implanted dopant comprises phosphorous, wherein the one or more second doped regions comprise a diffused dopant, wherein the diffused dopant is formed by introducing a dopant for diffusion in the form of phosphorous oxychloride (POCl 3 ), and wherein an additional dopant is diffused into a front surface of the base layer, creating misfit dislocations in the selective emitter layer to provide a sink for iron gettering: and injecting interstitials into the substrate to drive iron from substitutional sites into interstitial sites such that the iron diffuses rapidly to the gettering sink.
9. The solar cell of claim 8 , the selective emitter layer comprising a front surface, and the solar cell further comprising: an amorphous antireflection layer disposed on the front surface of the selective emitter layer.
10. The solar cell of claim 9 , the antireflection layer comprising a front surface, a base layer comprising a back surface, and the solar cell further comprising: one or more screen-printed front contacts disposed on the front surface of the antireflection layer in electrical communication with the selective emitter layer through the antireflection layer; and one or more screen-printed back contacts disposed on the back surface of the base layer.
11. The solar cell of claim 10 , wherein the one or more front contacts are aligned with the more heavily doped one or more first doped regions of the selective emitter layer to reduce contact resistance, and wherein the one or more front contacts are in electrical communication with the one or more first doped regions of the selective emitter layer.
12. The solar cell of claim 8 , wherein the p-n junction and the selective emitter layer are both formed during a single anneal cycle.