A-SI:H ABSORBER LAYER FOR A-SI SINGLE- AND MULTIJUNCTION THIN FILM SILICON SOLAR CELL

1 . Method for manufacturing a thin film solar cell, comprising the sequential steps of

a) depositing a positively doped Si layer ( 3 ),

b1) depositing a first intrinsic a-Si:H layer ( 21 ) at a first deposition rate,

b2) depositing a second intrinsic a-Si:H layer ( 22 ) at a second deposition rate, and

c) depositing a negatively doped Si layer ( 5 ), whereby

the second deposition rate is greater than the first deposition rate.

2 . Method according to the previous claim, whereby the first deposition rate is ≧40% and ≦75%, preferably ≧40% and ≦60%, of the second deposition rate, more preferably the first deposition rate is 2.1 Å/sec and the second deposition rate is 3.6 Å/sec.

3 . Method according to any of the previous claims, whereby the deposition of the layers ( 3 , 21 , 22 , 4 ) is carried out by a CVD process using RF power having during step b1) a level of ≧30% and ≦75%, preferably ≧30% and ≦50%, compared to the level during step b2).

4 . Method according to any of the previous claims, whereby the deposition of the layers ( 3 , 21 , 22 , 4 ) is carried out by a CVD process using hydrogen and silane as precursor gas having a hydrogen to silane flow ratio during step b1) of ≧1 and ≦1.5 compared to the hydrogen to silane flow ratio during step b2).

5 . Method according to any of the previous claims, whereby the deposition of the layers ( 3 , 21 , 22 , 4 ) is carried out by a CVD process having a process pressure during step b1) of ≧30% and ≦90% compared to the process pressure during step b2).

6 . Method according to any of the previous claims, whereby the first intrinsic a-Si:H layer ( 21 ) and the second intrinsic a-Si:H layer ( 22 ) are deposited such that the thickness of the first intrinsic a-Si:H layer ( 21 ) is ≧15% and ≦45%, preferably ≧15% and ≦35%, of the overall intrinsic a-Si:H layer ( 21 , 22 ) thickness of the first intrinsic a-Si:H layer ( 21 ) and the second intrinsic a-Si:H layer ( 22 ).

7 . Method according to any of the previous claims, whereby the positively doped Si layer ( 3 ) and/or the negatively doped Si layer ( 5 ) comprises a-Si:H or μc-Si:H.

8 . Method according to any of the previous claims, comprising the sequential steps of

providing a substrate ( 1 ),

depositing a first TCO layer ( 2 ) on the substrate ( 1 ),

depositing the layers ( 3 , 21 , 22 , 4 ) according to any of the previous claims on the first TCO layer ( 2 ), and

depositing a second TCO layer ( 6 ) on the deposited layers ( 3 , 21 , 22 , 4 ) according to any of the previous claims.

9 . Method for manufacturing a multi-junction thin film solar cell, comprising the sequential steps of

providing a substrate ( 1 , 12 ),

depositing a first TCO layer ( 2 , 22 ) on the substrate ( 1 , 12 ),

depositing the layers ( 3 , 21 , 22 , 4 ) according to any of the previous claims 1 to 7 on the first TCO layer ( 2 , 22 ) forming a top solar cell ( 9 ),

depositing at least one another solar cell ( 10 ) comprising in sequential order a positively doped Si layer ( 16 ), an intrinsic a-Si:H or μc-Si:H layer ( 17 ) and a negatively doped Si layer ( 18 ) on the top solar cell ( 9 ), and

depositing a second TCO layer ( 6 , 19 ) on the backmost another solar cell ( 10 ).

10 . Thin film solar cell, comprising

a positively doped Si layer ( 3 ),

a first intrinsic a-Si:H layer ( 21 ) deposited on the positively doped Si layer ( 3 ),

a second intrinsic a-Si:H layer ( 22 ) deposited on the first intrinsic a-Si:H layer ( 21 ), and

a negatively doped Si layer ( 5 ) deposited on the second intrinsic a-Si:H layer ( 22 ), whereby

the thickness of the first intrinsic a-Si:H layer ( 21 ) is ≧15% and ≦45%, preferably ≧15% and ≦35%, of the overall intrinsic a-Si:H layer ( 21 , 22 ) thickness of the first intrinsic a-Si:H layer ( 21 ) and the second intrinsic a-Si:H layer ( 22 ).

11 . Thin film solar cell according to claim 10 , whereby the first intrinsic a-Si:H layer ( 21 ) comprises a lower H-content c H incorporated in the intrinsic material than the second intrinsic a-Si:H layer ( 22 ), preferably the first intrinsic a-Si:H layer ( 21 ) comprises a H-content c H of ≧9% and ≦11%, most preferably of 10.1%, and the second intrinsic a-Si:H layer ( 22 ) comprises a H-content c H of ≧12% and ≦15%, most preferably of 13.7%.

12 . Thin film solar cell according to any of the previous claims 10 or 11 , whereby the first intrinsic a-Si:H layer ( 21 ) comprises a lower microstructure factor R than the second intrinsic a-Si:H layer ( 22 ), preferably the first intrinsic a-Si:H layer ( 21 ) comprises a microstructure factor R of ≧2% and ≦6%, most preferably of 3.9% and the second intrinsic a-Si:H layer ( 22 ) comprises a microstructure factor R of ≧8% and ≦13%, most preferably of 10.5%.

13 . Thin film solar cell according to any of the previous claims 10 to 12 , whereby the first intrinsic a-Si:H layer ( 21 ) comprises a denser intrinsic material characterised by less defects and/or less micro-voids incorporated in the intrinsic material than the second intrinsic a-Si:H layer ( 22 ).

14 . Thin film solar cell according to any of the previous claims 10 to 13 , whereby the first intrinsic a-Si:H layer ( 21 ) comprises a lower band gap energy than the second intrinsic a-Si:H layer ( 22 ), preferably the first intrinsic a-Si:H layer ( 21 ) comprises a band gap energy of ≧1810 eV and ≦1820 eV, most preferably of 1815 eV and the second intrinsic a-Si:H layer ( 22 ) comprises a band gap energy of ≧1825 eV and ≦1835 eV, most preferably of 1830 eV.

15 . Thin film solar cell according to any of the previous claims 10 to 14 , whereby the overall intrinsic a-Si:H layer ( 21 , 22 ) thickness of the first intrinsic a-Si:H layer ( 21 ) and the second intrinsic a-Si:H layer ( 22 ) is ≧100 nm and ≦2 μm, preferably 220 nm.