Back-side contact solar cell
The invention relates to a back-side contact solar cell including a semiconductor substrate, in particular a silicon wafer, including a front side and a back side, the solar cell having electrodes of a first polarity and electrodes of a second polarity on the back side, wherein a tunnel layer and a highly doped silicon layer are positioned under the electrodes of a first polarity, and the electrodes of the second polarity make direct electrical and mechanical contact with the semiconductor substrate.
1 . A method for producing a back-side contact solar cell, wherein a semiconductor substrate of the solar cell comprises a polished or textured back side and a textured front side, wherein the method comprises the steps of:
applying a first tunnel layer comprising silicon dioxide to a surface of the back side,
depositing a full-area, highly doped silicon layer of a first polarity on the first tunnel layer, the highly doped silicon layer of the first polarity comprising a first dopant,
applying a first precursor layer of a second polarity comprising a second dopant on the highly doped silicon layer of the first polarity, wherein concentrations of the first and second dopants in the highly doped silicon layer and the first precursor layer are such that an amount of the second dopant in the first precursor layer is higher than an amount of the first dopant in the highly doped silicon layer,
selectively laser irradiating regions of the first precursor layer and the highly doped silicon layer to locally produce highly doped base regions in the back side of the semiconductor substrate by overcompensation of the second dopant for the first dopant in the highly doped silicon layer, and
selectively removing parts of the highly doped silicon layer and the first precursor layer to expose the surface of the back side, including the highly doped base regions and edge regions that (i) separate remaining parts of the highly doped silicon layer and the highly doped base regions and (ii) define a space along the surface of the back side between the highly doped silicon layer and the highly doped base regions.
2 . The method according to claim 1 , wherein depositing the highly doped silicon layer comprises depositing undoped silicon and subsequently introducing the first dopant into the undoped silicon.
3 . The method according to claim 1 , further comprising depositing a second tunnel layer on the front side, and removing the second tunnel layer from the front side.
4 . The method according to claim 1 , further comprising, after selectively removing the parts of the first highly doped silicon layer and the first precursor layer, applying a passivation layer to each of a front side of the semiconductor substrate and the back side of the semiconductor substrate.
5 . The method according to claim 1 , further comprising applying electrodes to the back side of the solar cell.
6 . The method according to claim 4 , further comprising selectively removing parts of the passivation layer on the back side of the semiconductor substrate and applying electrodes to the back side of the semiconductor substrate where the parts of the passivation layer have been selectively removed.
7 . The method according to claim 1 , further comprising applying a second precursor layer comprising the second dopant on the front side of the semiconductor substrate, and diffusing the second dopant into the front side of the semiconductor substrate.
8 . The method according to claim 1 , wherein the first precursor layer comprises a phosphosilicate glass.
9 . The method according to claim 5 , wherein the electrodes comprise (i) first electrodes on the highly doped silicon layer and (ii) second electrodes in direct electrical and mechanical contact with the highly doped base regions.
10 . The method according to claim 6 , wherein the electrodes comprise (i) first electrodes that make direct contact with the highly doped silicon layer and (ii) second electrodes in direct electrical and mechanical contact with the highly doped base regions.
11 . The method according to claim 1 , wherein the first precursor layer and the highly doped silicon layer are selectively laser irradiated at an energy that locally melts the first precursor layer, the highly doped silicon layer, the first tunnel layer, and the surface of the back side to create the highly doped base regions.
12 . The method according to claim 11 , wherein the semiconductor substrate comprises silicon.
13 . The method according to claim 12 , wherein selectively laser irradiating regions of the first precursor layer and the highly doped silicon layer forms melted silicon on the surface of the back side of the semiconductor substrate, and diffuses the first dopant and the second dopant into the melted silicon.
14 . The method according to claim 13 , further comprising cooling and solidifying the melted silicon after selectively laser irradiating regions of the first precursor layer and the highly doped silicon layer.
15 . The method according to claim 14 , wherein one or both of the first and second dopants accumulates at the surface of the back side of the semiconductor substrate.
16 . The method according to claim 1 , wherein the semiconductor substrate comprises silicon.
17 . The method according to claim 1 , wherein selectively removing parts of the highly doped silicon layer and the first precursor layer comprises laser irradiation, wet chemical etching, or a combination thereof.
18 . The method according to claim 17 , wherein selectively removing parts of the highly doped silicon layer and the first precursor layer comprises wet chemical etching, and etching the highly doped silicon layer limits an increase in layer resistance of the highly doped silicon layer.