THIN-FILM SILICON TANDEM SOLAR CELL AND METHOD FOR MANUFACTURING THE SAME

1 . A photovoltaic cell comprising, deposited on a transparent substrate in the following order,

a first conductive oxide layer;

a first p-i-n junction;

a second p-i-n junction;

a second conductive oxide layer;

wherein

said first conductive oxide layer is substantially transparent and comprises a low-pressure chemical vapor deposited ZnO layer; and

said second conductive oxide layer comprises an at least partially transparent low-pressure chemical vapor deposited ZnO layer; and

wherein said first p-i-n junction comprises in the following order

a layer of p-doped a-Si:H deposited using PECVD and having at its end region facing toward said second p-i-n junction a higher band gap than at its end region facing toward said first conductive oxide layer;

a buffer layer of a-Si:H deposited using PECVD without voluntary addition of a dopant;

a layer of substantially intrinsic a-Si:H deposited using PECVD;

a first layer of n-doped a-Si:H deposited using PECVD; and

a layer of n-doped μc-Si:H deposited using PECVD; and

wherein said second p-i-n junction comprises in the following order a layer of p-doped μc-Si:H deposited using PECVD;

a layer of substantially intrinsic μc-Si:H deposited using PECVD; and

a second layer of n-doped a-Si:H deposited using PECVD.

2 . The photovoltaic cell according to claim 1 , wherein for a thickness d TCO of said first conductive oxide layer applies 1 μm≦d TCO ≦4 μm, more particularly 1.3 μm≦d TCO ≦3 μm, and wherein for said thickness d TCO and for a thickness d i of said layer of substantially intrinsic μc-Si:H applies 1.25≦(d TCO /μm)·(d i /μm−0.4)≦2, more particularly 1.35≦(d TCO /μm)·(d i /μm−0.4)≦1.85.

3 . The photovoltaic cell according to claim 1 or claim 2 , wherein said bandgap of said layer of p-doped a-Si:H at said end region facing toward said second p-i-n junction is higher than said bandgap of said layer of p-doped a-Si:H at said end region facing toward said first conductive oxide layer by at least 0.15 eV, more particularly by at least 0.2 eV and at most 0.5 eV.

4 . The photovoltaic cell according to any of the preceding claims, wherein said layer of p-doped a-Si:H comprises

a first layer of p-doped a-Si:H deposited using PECVD; and

a second layer of p-doped a-Si:H deposited using PECVD and having a higher band gap than said first layer of p-doped a-Si:H.

5 . The photovoltaic cell according to claim 4 , wherein a thickness of said first layer of p-doped a-Si:H is at most 10 nm, in particular at most 7 nm, and wherein a thickness of said second layer of p-doped a-Si:H is at least 5 nm and at most 16 nm, and wherein said thickness of said second layer of p-doped a-Si:H is larger than said thickness of said first layer of p-doped a-Si:H.

6 . The photovoltaic cell according to one of the preceding claims, comprising in the before-described sequence of layers immediately before said layer of p-doped μc-Si:H a first oxide layer having a thickness of less than 2.5 nm, in particular less than 2 nm, more particularly between 0.1 nm and 1.5 nm.

7 . The photovoltaic cell according to one of the preceding claims, comprising in the before-described sequence of layers immediately before said second conductive oxide layer a second oxide layer having a thickness of less than 2.5 nm, in particular less than 2 nm, more particularly between 0.1 nm and 1.5 nm.

8 . The photovoltaic cell according to one of the preceding claims, comprising in the before-described sequence of layers immediately before said layer of n-doped μc-Si:H a third oxide layer having a thickness of less than 2.5 nm, in particular less than 2 nm, more particularly between 0.1 nm and 1.5 nm.

9 . The photovoltaic cell according to one of the preceding claims, wherein said buffer layer has a thickness of at least 2 nm and at most 15 nm, more particularly of at least 5 nm and at most 12 nm.

10 . The photovoltaic cell according to one of the preceding claims, wherein said buffer layer is deposited using PECVD at a growth rate smaller than a growth rate of the deposition of said layer of p-doped a-Si:H, and in particular is deposited using PECVD at a growth rate of at most half of a growth rate of the deposition of said layer of p-doped a-Si:H.

11 . The photovoltaic cell according to one of the preceding claims, wherein a thickness d i of said layer of substantially intrinsic μc-Si:H is at least 0.8 μm and at most 2 μm, more particularly at least 1 μm and at most 1.6 μm.

12 . The photovoltaic cell according to one of the preceding claims, wherein a thickness d i of said layer of substantially intrinsic μc-Si:H is at least 4 times and at most 8 times as large as a thickness of said layer of substantially intrinsic a-Si:H.

13 . The photovoltaic cell according to one of the preceding claims, wherein a thickness of a layer stack starting with and including said first layer of n-doped a-Si:H and ending with and including said layer of n-doped μc-Si:H is at least 10 nm and at most 50 nm.

14 . The photovoltaic cell according to one of the preceding claims, wherein a thickness of said second conductive oxide layer is at most 1.8 μm, in particular between 1.4 μm and 1.7 μm.

15 . A photovoltaic converter panel comprising at least one photovoltaic cell according to one of the preceding claims.

16 . The photovoltaic converter panel according to claim 15 , comprising a multitude of photovoltaic cells according to one claims 1 to 14 and having a surface extent of at least 2500 cm 2 .

17 . Method for manufacturing a photovoltaic cell or a photovoltaic converter panel, comprising the steps of depositing on a transparent substrate in the following order:

b) a first conductive oxide layer;

c) a first p-i-n junction;

d) a second p-i-n junction;

e) a second conductive oxide layer;

wherein step b) comprises depositing a substantially transparent ZnO layer by means of low-pressure chemical vapor deposition; and

step e) comprises depositing an at least partially transparent ZnO layer by means of low-pressure chemical vapor deposition; and

wherein step c) comprises the following steps in the following order:

c0) depositing a layer of p-doped a-Si:H by means of PECVD in such a way that it has at its end region facing toward said second p-i-n junction a higher band gap than at its end region facing toward said first conductive oxide layer;

c4) depositing a buffer layer of a-Si:H by means of PECVD without voluntary addition of a dopant;

c5) depositing a layer of substantially intrinsic a-Si:H by means of PECVD;

c6) depositing a first layer of n-doped a-Si:H by means of PECVD; and

c7) depositing a layer of n-doped μc-Si:H by means of PECVD; and

wherein step d) comprises the following steps in the following order:

d1) depositing a layer of p-doped μc-Si:H by means of PECVD;

d2) depositing a layer of substantially intrinsic μc-Si:H by means of PECVD; and

d3) depositing a second layer of n-doped a-Si:H deposited by means of PECVD.

18 . The method according to claim 17 , characterized in being a method for large-scale industrial manufacturing of photovoltaic cells and photovoltaic converter panels, respectively, in particular of photovoltaic converter panels of at least 2500 cm 2 surface extent.

19 . The method according to claim 17 or claim 18 , wherein in said depositing steps, deposition parameters and deposition times are chosen such that for a thickness d TCO of said first conductive oxide layer applies 1 μm≦d TCO ≦4 μm, more particularly 1.3 μm≦d TCO ≦3 μm;

a thickness of said layer of p-doped a-Si:H is at least 8 nm and at most 20 nm, in particular at least 9 nm and at most 17 nm;

said buffer layer has a thickness of at least 2 nm and at most 15 nm, more particularly of at least 5.5 nm and at most 12 nm;

said layer of substantially intrinsic a-Si:H has a thickness of at least 150 nm and at most 350 nm, more particularly of at least 180 nm and at most 310 nm;

a thickness of a layer stack starting with and including said first layer of n-doped a-Si:H and ending with and including said layer of n-doped μc-Si:H is at least 10 nm and at most 50 nm;

said layer of p-doped μc-Si:H has a thickness of at least 10 nm and at most 30 nm;

a thickness d i of said layer of substantially intrinsic μc-Si:H is at least 0.8 μm and at most 2 μm, more particularly at least 1 μm and at most 1.6 μm;

said second layer of n-doped a-Si:H has a thickness of at least 10 nm and of at most 50 nm, in particular of 30 nm±10 nm;

a thickness of said second conductive oxide layer is at most 1.8 μm, in particular between 1.4 μm and 1.7 μm.

20 . The method according to one of claims 17 to 19 wherein step c0) comprises the steps of

c1) depositing a first layer of p-doped a-Si:H by means of PECVD;

c2) depositing a second layer of p-doped a-Si:H by means of PECVD having a higher band gap than said first layer of p-doped a-Si:H.

21 . The method according to claim 20 , wherein

in step c1), deposition parameters and deposition times are chosen such that a thickness of said first layer of p-doped a-Si:H is at most 10 nm, in particular at most 7 nm; and wherein

in step c2), deposition parameters and deposition times are chosen such that a thickness of said second layer of p-doped a-Si:H is larger than said thickness of said first layer of p-doped a-Si:H, and in particular such that said thickness of said second layer of p-doped a-Si:H is at least 5 nm and at most 16 nm.

22 . The method according to one of claims 17 to 21 , comprising carrying out after step c0) and before step c4) the step of

c3) exposing said second layer of p-doped a-Si:H to a vapor or gas comprising water or an alcohol.

23 . The method according to one of claims 17 to 22 , comprising depositing said buffer layer at a growth rate smaller than a growth rate of the deposition of said layer of p-doped a-Si:H in step c0), in particular depositing said buffer layer at a growth rate of at most half of a growth rate of the deposition of said layer of p-doped a-Si:H in step c0).

24 . The method according to one of claims 17 to 23 , comprising carrying out after step c7) and before step d1) the step of

c8) exposing said layer of n-doped μc-Si:H to an oxygen-containing plasma, in particular to a plasma containing besides oxygen also phosphorus, for forming a first oxide layer having a thickness of less than 2.5 nm, in particular less than 2 nm, more particularly between 0.1 nm and 1.5 nm.

25 . The method according to one of claims 17 to 24 , comprising carrying out after step d3) and before step e) the step of

d4) creating a second oxide layer by carrying out one of the steps of

d4′) exposing said second layer of n-doped a-Si:H to an oxygen-containing plasma, for forming said second oxide layer;

and

d4″) depositing said second oxide layer onto said second layer of n-doped a-Si:H using PECVD using a feed gas comprising an oxygen-containing gas species and a silicon-containing gas species;

wherein said second oxide layer has a thickness of less than 2.5 nm, in particular less than 2 nm, more particularly between 0.1 nm and 1.5 nm.

26 . The method according to one of claims 17 to 25 , comprising carrying out after step c6) and before step c7) the step of

c65) exposing said first layer of n-doped a-Si:H to an oxygen-containing plasma, in particular to a plasma containing besides oxygen also phosphorus, for forming a third oxide layer having a thickness of less than 2.5 nm, in particular less than 2 nm, more particularly between 0.1 nm and 1.5 nm.