6 Amorphous Silicon Solar Cells
159
a structure without voids. On the other hand, it is important to deposit the intrinsic
(i) microcrystalline layer (which serves as the absorber layer and plays the decisive
role of absorbing photons and generating holes and electrons) on a highly crystalline
p-type layer. Otherwise, the i-layer will start its growth, during the first 50 nm, in the
amorphous phase—leading, thereby, to solar cells, which are completely unusable.
6.3.3 The Microcrystalline/Amorphous or “Micromorph”
Tandem Solar Cell
Microcrystalline silicon solar cells have been used as bottom cells, in a tandem structure, together with amorphous silicon top cells, to form what was called the “micromorph” tandem solar cell. The corresponding cell structure is shown in Fig. 6.23.
These tandem cells were, in the period 2005–2009, considered to be one of the most
promising options for future Photovoltaics. The reasons being the following:
(a) These cells use a very low quantity of silicon base material
(b) They have potentially a very low manufacturing cost
(c) No toxic materials are involved in the cell structure
(d) Very low-cost mass production seemed imminent
(e) The combination of microcrystalline silicon and amorphous silicon constitute
theoretically the ideal combination of two different bandgaps for a tandem cell
[17].
Indeed in 2016, relatively high module efficiencies (of over 10%) were reported
by Industrial R and D laboratories [18].
In the years 2007–2009, many Industries invested heavily in the purchase of
equipment for the large-scale production of modules based on micromorph tandems.
ZnO
μc-Si:H
a-Si:H
ZnO
glass
Micromorph
Fig. 6.23 a-Si:H/µc-Si:H or “micromorph” tandem solar cell: a basic structure; b electron
micrograph. Reproduced from [1], with the kind permission of the EPFL Press
159
a structure without voids. On the other hand, it is important to deposit the intrinsic
(i) microcrystalline layer (which serves as the absorber layer and plays the decisive
role of absorbing photons and generating holes and electrons) on a highly crystalline
p-type layer. Otherwise, the i-layer will start its growth, during the first 50 nm, in the
amorphous phase—leading, thereby, to solar cells, which are completely unusable.
6.3.3 The Microcrystalline/Amorphous or “Micromorph”
Tandem Solar Cell
Microcrystalline silicon solar cells have been used as bottom cells, in a tandem structure, together with amorphous silicon top cells, to form what was called the “micromorph” tandem solar cell. The corresponding cell structure is shown in Fig. 6.23.
These tandem cells were, in the period 2005–2009, considered to be one of the most
promising options for future Photovoltaics. The reasons being the following:
(a) These cells use a very low quantity of silicon base material
(b) They have potentially a very low manufacturing cost
(c) No toxic materials are involved in the cell structure
(d) Very low-cost mass production seemed imminent
(e) The combination of microcrystalline silicon and amorphous silicon constitute
theoretically the ideal combination of two different bandgaps for a tandem cell
[17].
Indeed in 2016, relatively high module efficiencies (of over 10%) were reported
by Industrial R and D laboratories [18].
In the years 2007–2009, many Industries invested heavily in the purchase of
equipment for the large-scale production of modules based on micromorph tandems.
ZnO
μc-Si:H
a-Si:H
ZnO
glass
Micromorph
Fig. 6.23 a-Si:H/µc-Si:H or “micromorph” tandem solar cell: a basic structure; b electron
micrograph. Reproduced from [1], with the kind permission of the EPFL Press