METHOD OF COATING A SUBSTRATE FOR MANUFACTURING A SOLAR CELL
The invention relates to a method of coating a substrate for manufacturing a solar cell in a deposition environment, the method comprising the steps of: a) Depositing a first zinc oxide layer onto a substrate. Reducing a zinc precursor content in the deposition environment, c) Treating the first zinc oxide layer with a mixture of diborane and water to form a plurality of coating seeds on the surface of the first zinc oxide layer, and d) Depositing a second zinc oxide layer onto the first zinc oxide layer. The method according to the invention allows improving the material quality of silicon layers which may later be grown on such a substrate. Additionally, the light scattering and subsequent light trapping in a respective solar cell may be enhanced by a method according to the invention. The present invention further relates to a solar cell being manufactured according to the invention.
1 . Method of coating a substrate ( 41 ) in a deposition environment for manufacturing a solar cell ( 40 ), the method comprising the steps of:
a) Depositing a first zinc oxide layer onto a substrate ( 41 ),
b) Reducing a zinc precursor content in the deposition environment,
c) Treating the first zinc oxide layer with a mixture of diborane and water to form a plurality of coating seeds on the surface of the first zinc oxide layer, and
d) Depositing a second zinc oxide layer onto the first zinc oxide layer.
2 . Method according to claim 1 , whereby step b) is accomplished by one or more of the steps comprising
Stopping an inflow of the zinc precursor material into the deposition environment,
Pumping the deposition environment to provide a lower precursor concentration, and/or
Purging the deposition environment by introducing one or more of water, diborane, nitrogen and/or hydrogen.
3 . Method according to claim 1 , whereby the step of depositing a first zinc oxide layer within step a) and/or the step of depositing a second zinc oxide layer within step d) is performed by a LPCVD process.
4 . Method according to claim 1 , whereby the first zinc oxide layer is treated with a mixture of diborane and water in a relation lying in the range of 1:2 to 1:4 in step c).
5 . Method according to claim 1 , whereby the mixture of diborane and water is at least partly removed from the substrate ( 41 ) before performing step d).
6 . Method according to claim 1 , whereby step a) and step d) are performed in different deposition chambers, and whereby step c) is performed in a further treatment chamber whilst the substrate ( 41 ) is delivered from the first deposition chamber to the second deposition chamber.
7 . Method according to claim 1 , whereby the first zinc oxide layer is deposited to have a lower degree of doping compared to the second zinc oxide layer.
8 . Method according to claim 1 , whereby the first zinc oxide layer is deposited to have a higher degree of doping compared to the second zinc oxide layer.
9 . Method according to claim 1 , whereby at least three layers are subsequently deposited, whereby the layers have a degree of doping being subsequently decreasing from the first zinc oxide layer to the following zinc oxide layers, and whereby steps b) and c) are performed during respective deposition steps.
10 . Method according to claim 1 , whereby the first zinc oxide layer is deposited to have an equal degree of doping compared to the second zinc oxide layer.
11 . Method according to claim 1 , whereby at least three zinc oxide layers are subsequently deposited, whereby a middle zinc oxide layer has a degree of doping being smaller compared to the adjacent layers, and whereby steps b) and c) are performed during respective deposition steps.
12 . Method according to claim 1 , whereby the first zinc oxide layer is deposited to have a greater thickness compared to the second zinc oxide layer.
13 . Method according to claim 1 , whereby the composition and/or temperature is modified during step a) and/or d).
14 . Solar cell, comprising at least one substrate ( 41 ) being coated by a method according to claim 1 .