Solar cell and method for producing a solar cell

Abstract

The invention relates to a solar cell comprising: a substrate (1) having a front side (11) and a rear side (12); a tunnel oxide layer (2) which is disposed on the rear side (12); a phosphorus-containing poly-Si layer (3) which is disposed on a side of the tunnel oxide layer (2) facing away from the rear side (12); and an oxygen-containing layer (4) which is selected from the group consisting of an oxygen- and phosphorus-containing polysilicon layer, a silicon oxide layer or a silicon oxynitride layer and which is disposed on a side of the phosphorus-containing poly-Si layer (3) facing away from the rear side (12) and which has a layer thickness in the range of 10 to 50 nm, wherein a total layer thickness of the phosphorus-containing poly-Si layer (3) and the oxygen-containing layer (4) is less than 100 nm. The invention also relates to a method for producing a solar cell of this type.

Description

[0001] Title: Solar cell and method for manufacturing a solar cell

[0002] Description:

[0003] The invention relates to a solar cell and a method for manufacturing a solar cell. In particular, the invention relates to a solar cell comprising a substrate, a tunnel oxide layer, and a poly-Si layer, and a method for manufacturing the same. The substrate has a front and a back. During operation, the front is the side facing the light, while the back is the side facing away from the light.

[0004] If the tunnel oxide layer is located on the back of the substrate, and the poly-Si layer is located on the side of the tunnel oxide layer facing away from the substrate, it is a so-called TopCon (Tunnel Oxide Passivated Contact) solar cell. Such a TopCon solar cell exhibits good efficiency. However, there is still a need to improve it.

[0005] It is an object of the present invention to provide a solar cell and a method for manufacturing a solar cell with improved efficiency.

[0006] According to the invention, this problem is solved by a solar cell having the features of claim 1 and a method having the features of claim 6. Advantageous further developments and modifications are specified in the dependent claims.

[0007] The oxygen-containing layer binds phosphorus, which has a positive effect on contactability and low contact resistance. The total thickness of the phosphorus-containing poly-Si layer and the oxygen-containing layer is less than 100 nm, thus minimizing absorption losses and reducing the consumption of relatively expensive process gases such as SiH4 and PH3, which are used in the production of the solar cell. The solar cell exhibits a higher efficiency than a solar cell that does not contain the oxygen-containing layer.

[0008] The invention relates to a solar cell comprising a substrate with a front and a back, a tunnel oxide layer arranged on the back, a phosphorus-containing poly-Si layer arranged on a side of the tunnel oxide layer facing away from the back, and an oxygen-containing layer selected from the group consisting of an oxygen- and phosphorus-containing poly-silicon layer, a silicon oxide layer, or a silicon oxynitride layer arranged on a side of the phosphorus-containing poly-Si layer facing away from the back, and having a layer thickness in the range of 10 to 50 nm, wherein the total layer thickness of the phosphorus-containing poly-Si layer and the oxygen-containing layer is less than 100 nm.

[0009] The solar cell exhibits both low layer resistance and good transverse conductivity, as well as low contact resistance to a backside metallization and relatively low absorption.

[0010] In particular, the back-side layer stack is characterized by a low layer resistance and / or high transverse conductivity, while simultaneously offering good contactability via a back-side electrode.

[0011] The term "oxygen- and phosphorus-containing poly-Si layer" refers to an oxygen- and phosphorus-doped or oxygen- and phosphorus-enriched poly-Si layer. The term "phosphorus-containing poly-Si layer" refers to a phosphorus-doped or phosphorus-enriched poly-Si layer. The term "doping" is usually used to describe a concentration of a foreign atom, in this case phosphorus and possibly other elements.

[0012] Oxygen is used in concentrations between 0.1 and 100 ppm in the poly-Si layer, while the term "enrichment" is used for concentrations of phosphorus and, if present, oxygen above 100 ppm in the poly-Si layer. The expression "oxygen- and phosphorus-containing poly-Si layer" or "phosphorus-containing poly-Si layer" encompasses both doping of the poly-Si layer with phosphorus and, if present, oxygen, and enrichment of phosphorus and, if present, oxygen within the poly-Si layer.

[0013] The thickness of the oxygen-containing layer is preferably 11 to 30 nm. The total thickness of the phosphorus-containing poly-Si layer and the oxygen-containing layer is preferably less than 80 nm.

[0014] In a preferred embodiment, the oxygen-containing layer is formed as an oxygen- and phosphorus-containing poly-Si layer and has a higher phosphorus content than the phosphorus-containing poly-Si layer or the poly-silicon layer. The higher phosphorus content in the oxygen-containing layer in the form of the oxygen- and phosphorus-containing poly-Si layer is advantageous for contact formation.

[0015] Preferably, the oxygen-containing layer is formed as a silicon oxide layer. Alternatively, preferably, the oxygen-containing layer is formed as a silicon oxynitride layer. Preferably, the silicon oxide layer or the silicon oxynitride layer is free of phosphorus as a doping or enrichment material.

[0016] Preferably, the thickness of the phosphorus-containing poly-Si layer is less than 80 nm, more preferably less than 50 nm. Preferably, the thickness of the phosphorus-containing poly-Si layer is in the range of 20 to 80 nm, more preferably 30 to 50 nm.

[0017] In a preferred embodiment, an intermediate layer is arranged between the phosphorus-containing poly-Si layer and the oxygen-containing layer. The intermediate layer is preferably designed as a poly-Si layer that can contain both oxygen and phosphorus. Preferably, the solar cell is configured as a bifacial top-cone solar cell.

[0018] This results in a further improved efficiency.

[0019] Preferably, the substrate is a silicon substrate. Preferably, the substrate is a wafer. More preferably, the substrate is a silicon wafer. The tunnel oxide layer can be made of silicon dioxide or aluminum oxide. The thickness of the tunnel oxide layer is preferably in the range of 1 to 3 nm.

[0020] The invention further relates to a method for manufacturing a solar cell, comprising the following steps: a) providing a substrate with a front and a back side, b) applying a tunnel oxide layer to the back side, c) applying an amorphous Si layer to the tunnel oxide layer using phosphorus as a doping or enrichment agent by means of a PECVD or LPCVD process, d) applying an oxygen-containing layer to the amorphous Si layer by means of the PECVD or LPCVD process, and e) annealing the substrate with the applied tunnel oxide layer, the applied amorphous Si layer and the applied oxygen-containing layer.

[0021] The deposition of the silicon or Si layers initially takes place as an amorphous layer, i.e., as a-Si(n):H or a-SiOx(n):H or SiOx:H or SiOxNy:H. During the subsequent annealing process, which is preferably a heat treatment or annealing process at 800 to 950 °C for a period of 10 to 60 minutes, hydrogen diffuses out of the Si layers, which transition from the amorphous state to the polycrystalline state during annealing. The process is preferably carried out in a tubular PECVD system or an LPCVD system. In a preferred embodiment, step c) is performed using a silicon-containing gas and a phosphorus-containing gas, preferably using SiH4, Hα, and PH3. This allows the amorphous, phosphorus-containing Si layer to be produced simply in one step.

[0022] Preferably, step d) is carried out using an oxygen-containing molecular gas and a silicon-containing gas. If phosphorus doping or enrichment of the resulting layer is to be achieved in step d), step d) is preferably carried out using an oxygen-containing molecular gas, a silicon-containing gas, and a phosphorus-containing gas. Preferably, N₂O, CO₂, NO₂, NO, or CO is used as the oxygen-containing molecular gas. Preferably, SiH₄ is ​​used as the silicon-containing gas. Preferably, PH₃ is used as the optional phosphorus-containing gas, preferably diluted in H₂.

[0023] In a preferred embodiment, step d) is carried out using the oxygen-containing molecular gas, the silicon-containing gas, and the phosphorus-containing gas, wherein the partial pressure of the phosphorus-containing gas used is higher than the partial pressure of the phosphorus-containing gas used in step c). This results in a higher phosphorus content in the oxygen-containing layer, which is advantageous for contact formation.

[0024] Preferably, the partial pressure of the phosphorus-containing gas used in step d) is higher than the partial pressure of the phosphorus-containing gas used in step c). Preferably, the flux of the phosphorus-containing gas in step d) is at least 3 times higher than in step c). The amorphous silicon layer, a-Si:H(n), produced in step c) is preferably deposited with a low flux of the phosphorus-containing gas so that it exhibits good transverse conductivity. The partial pressure of the phosphorus-containing gas in step c) is preferably less than 1% relative to the other process gases, while in step d) it is preferably more than 1% relative to the other process gases.

[0025] In a preferred embodiment, step c) and / or step d) is / are carried out at a temperature of 300 to 500 °C, preferably 450 to 500 °C, and / or a pressure of 0.5 to 10 mbar, preferably 1.0 to 3.0 mbar. These temperatures and / or pressures are sufficient to achieve good results in layer formation.

[0026] Preferably, the layers produced in steps c) and d) are applied exclusively to the back of the substrate.

[0027] Step b) can be carried out using PECVD or ALD (atomic layer deposition). The tunnel oxide layer can be formed from silicon dioxide or aluminum oxide. The tunnel oxide layer produced in step b) preferably has a thickness in the range of 1 to 3 nm.

[0028] In a preferred embodiment, step c) comprises the following sub-steps: c1) deposition of the phosphorus-containing silicon layer onto the substrate for a predetermined first duration and / or until a predetermined first layer thickness is reached, c2) exposure of the substrate and the phosphorus-containing silicon layer to a plasma using an uncoated process gas for a predetermined second duration or interruption of the plasma for approximately 10–60 seconds, c3) resumption of the deposition of the phosphorus-containing silicon layer onto the

[0029] The substrate is removed for a predetermined third time period and / or until a predetermined second layer thickness of the phosphorus-containing silicon layer is reached. This procedure results in a seed layer produced by steps c1) and c2). The seed layer deposited in step c1) is relatively thin compared to the layer produced in step c3) and has, for example, a layer thickness of 1 nm. The Si layer produced in step c3), on the other hand, has a layer thickness of at least 20 nm. By producing the seed layer, the phosphorus doping profile or phosphorus enrichment profile and the crystallinity of the phosphorus-containing poly-Si layer produced in step d) can be positively influenced.

[0030] In a preferred embodiment, the process is carried out in a PECVD (plasma-enhanced chemical vapor deposition) system or an LPCVD (low-pressure chemical vapor deposition) system. The PECVD or LPCVD system is preferably designed as a tube furnace. By using a tube PECVD or tube LPCVD system, the layers produced in the respective steps can be deposited in their respective sequence by changing the process gas flow over time, without having to move the substrate with its back-side layer stack or interrupt the vacuum.

[0031] The process is preferably carried out in a PECVD system. In a preferred embodiment, a pulsed, capacitively coupled low-pressure plasma is ignited between the multiple substrates, preferably in the frequency range of 40 to 400 kHz and / or with a power range of 2 to 20 kW.

[0032] Preferably, step a) comprises providing a plurality of substrates arranged in a wafer boat. Preferably, the substrates to be coated are loaded into a graphite wafer boat in which the substrates face each other in pockets and are contacted by means of contact pins. This reduces manufacturing costs. Preferably, the substrate is a wafer, more preferably a silicon wafer. Further features and advantages of the invention are explained in more detail in the context of the preferred embodiments described below. The figure is shown schematically and not to scale.

[0033] Fig. 1 shows a cross-sectional view of a solar cell according to a first embodiment of the invention;

[0034] Fig. 2 shows a cross-sectional view of a solar cell according to a second embodiment of the invention;

[0035] Fig. 3 shows a flowchart of a method according to the invention.

[0036] Fig. 1 shows a cross-sectional view of a solar cell according to a first embodiment of the invention. The solar cell has a substrate 1 with a front side 11 and a back side 12. Furthermore, the solar cell has a tunnel oxide layer 2 arranged on the back side 12, a phosphorus-containing poly-Si layer 3 arranged on one side of the tunnel oxide layer 2 facing away from the back side 12, and an oxygen-containing layer 4 arranged on one side of the phosphorus-containing poly-Si layer 3 facing away from the back side 12. The oxygen-containing layer 4 is selected from the group consisting of an oxygen- and phosphorus-containing poly-silicon layer, a silicon oxide layer, or a silicon oxynitride layer.

[0037] Fig. 2 shows a cross-sectional view of a solar cell according to a second embodiment of the invention. The solar cell shown in Fig. 2 corresponds to the solar cell shown in Fig. 1, with the difference that an intermediate layer 5 is arranged between the phosphorus-containing poly-Si layer 3 and the oxygen-containing layer 4. The intermediate layer 5 can be designed as a poly-Si layer that may contain both oxygen and phosphorus.

[0038] Fig. 3 shows a flowchart of a process according to the invention. The process is used to manufacture a solar cell and comprises the following steps. First, step a) is performed, in which a substrate with a front and a back side is provided. Step a) is followed by step b) in which a tunnel oxide layer is applied to the back side of the substrate. Step b) is followed by step c) in which an amorphous silicon layer is applied to the tunnel oxide layer using phosphorus as a doping or enrichment agent by means of a PECVD or LPCVD process. Step c) is followed by step d) in which an oxygen-containing layer is applied to the amorphous silicon layer by means of the PECVD or LPCVD process. Step d) is followed by step e) in which the substrate with the applied tunnel oxide layer, the applied amorphous silicon layer, and the applied oxygen-containing layer is annealed.

[0039] Reference symbol list:

[0040] 1 substrate

[0041] 11 Front 12 Back

[0042] 2 Tunnel oxide layer

[0043] 3 poly-Si layer

[0044] 4 oxygenated layer

[0045] 5 Intermediate layer

Claims

Patent claims:

1. Solar cell, comprising - a substrate (1 ) with a front (11 ) and a back (12), - a tunnel oxide layer (2) arranged on the back side (12), - a phosphorus-containing poly-Si layer (3) arranged on a side of the tunnel oxide layer (2) facing away from the back (12), and - an oxygen-containing layer (4) selected from the group consisting of an oxygen- and phosphorus-containing poly-silicon layer, a silicon oxide layer or a silicon oxynitride layer, arranged on a side of the phosphorus-containing poly-Si layer (3) facing away from the back side (12) and having a layer thickness in the range of 10 to 50 nm, wherein the total layer thickness of the phosphorus-containing poly-Si layer (3) and the oxygen-containing layer (4) is less than 100 nm.

2. Solar cell according to claim 1, characterized in that the oxygen-containing layer (4) is designed as the oxygen- and phosphorus-containing poly-Si layer and has a higher phosphorus content than the poly-Si layer (3).

3. Solar cell according to claim 1, characterized in that the oxygen-containing layer (4) is formed as a silicon oxide layer or as a silicon oxynitride layer, and is free of phosphorus as a doping or enrichment material.

4. Solar cell according to one of the preceding claims, characterized in that the layer thickness of the phosphorus-containing poly-Si layer (3) is less than 80 nm, preferably less than 50 nm, more preferably in the range of 20 to 80 nm, and even more preferably in the range of 30 to 50 nm.

5. Solar cell according to one of the preceding claims, characterized in that an intermediate layer (5) is arranged between the phosphorus-containing poly-Si layer (3) and the oxygen-containing layer (4) and / or that the solar cell is designed as a bifacial TopCon solar cell.

6. A method for manufacturing a solar cell, comprising the following steps: a) providing a substrate (1) having a front (11) and a back (12), b) applying a tunnel oxide layer (2) to the back (12), c) applying an amorphous Si layer to the tunnel oxide layer (2) using phosphorus as a doping or enrichment agent by means of a PECVD or LPCVD process, d) applying an oxygen-containing layer (4) to the amorphous Si layer by means of the PECVD or LPCVD process, and e) annealing the substrate (1) with the applied tunnel oxide layer (2), the applied amorphous Si layer and the applied oxygen-containing layer (4).

7. Method according to claim 6, characterized in that step c) is carried out using a silicon-containing gas and a phosphorus-containing gas, preferably using SiH4, H? and PH?.

8. Method according to claim 6 or 7, characterized in that step d) is carried out using an oxygen-containing molecular gas, a silicon-containing gas and optionally a phosphorus-containing gas, preferably using N2O, CO2, NO2, NO or CO as the oxygen-containing molecular gas, SiH4 as the silicon-containing gas, and optionally PH? as the optional phosphorus-containing gas.

9. Method according to claim 8, characterized in that step d) is carried out using the oxygen-containing molecular gas, of silicon-containing gas and phosphorus-containing gas is carried out, wherein a partial pressure of the phosphorus-containing gas used is higher than the partial pressure of the phosphorus-containing gas used in step c), wherein preferably the partial pressure of the phosphorus-containing gas used in step d) is higher than the partial pressure of the phosphorus-containing gas used in step c).

10. Method according to any one of claims 6 to 9, characterized in that step c) and / or step d) is or are carried out at a temperature of 300 to 500 °C, preferably 450 to 500 °C and / or a pressure of 0.5 to 10 mbar, preferably 1.0 to 3.0 mbar.

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