Solar Cell Technologies
Crystalline solar cells
Polycrystalline as well as monocrystalline solar cells belong into this group. The basic form for crystalline solar cells production is silicon ingot (please see production procedure description above). The ingot (block of silicon), sawn with diamond saw into thin silicon wafers, is a foundation for solar cell production. Wafers of 1 mm in thickness sawn with 1/10 mm precision are placed between two plan-parallel metal plates, which rotate into opposite directions. The procedure enables wafer thickness adjustment to 1/1000 mm precisely. The subsequent solar cell production procedure consists of the following steps:
Doped wafers are first etched some micro-metres deep. The procedure removes crystal-structure irregularities caused by sawing and provides wafer cleaning. The material is doped as melt at polycrystal silicon or adequate gas is added whilst extracting pure silicon.
The above procedure is followed by diffusion. Phosphorus, which is supplied inside the material in gaseous form, diffuses at the temperature of 800°C. N doped layer and oxide layer rich with phosphorus form on top of wafers due to oxygen reaction.
Wafers are then folded to form a cube and etched in oxygen plasma, removing N layer from the edges.
The following phase removes oxide layers from top of wafer by wet chemical etching.
In the back, contact surface is produced from silver containing 1% aluminium. Special procedures enable silver print over mask on cell surface.
Pressed cells are then sintered at high temperatures.
Similar procedure is used to print contacts in the front cell surface.
Anti-reflex layer is applied in a similar manner. We have titanium paste at choice, which at sintering form titanium dioxide TiO2 or silicon nitride Si3N4.
Amorphous solar cells
Amorphous solar cells are produced with similar technological procedures than integrated circuits. Due to the procedure these modules are also known as thin-film solar cells (thin-film modules). Herein, amorphous solar cells production is described briefly:
Glass substrate is thoroughly cleaned.
Lower contact layer is applied
The surface is then structured – divided into bands.
In vacuum, under high frequency electric field amorphous silicon layer is applied.
The surface is re-banded.
Upper metal electrodes are fixated.
Other solar cells
Among less frequently used solar cell types we find solar cells produced by EFG (Edge Defined Film fed Growth) method and Apex solar cells from silicon, cadmium telluride solar cells and copper-indium selenide (CIS) solar cells. EFG monocrystalline solar cells are produced directly from silicon melt eliminating sawing to wafers, which results in lower production costs and material saving for there is no waste due to sawing. Using EFG procedure, a silicon ribbon shaped in proper tube with eight flat sides is drawn from silicon melt. The tube length amounts to several metres. Flat sides are sawn by laser into separate solar cells. Most solar cells are proper square shaped in dimension of 100×100 mm. Consequently, the module power is greater with lesser surface compared to crystal modules of square shaped cells with truncated sides. Contacts are made in shape of copper bands. Separate cells are then combined in a similar manner than with other cell types. EFG cells are produced by Schott Solar. In contrast to EFG cells, Apex cells are poly-crystalline. Their production procedure is protected. Production procedure was developed by Astropower Inc. Cadmium telluride and copper-indium selenide (CIS) cells are thus far scarcely used, mostly in lab research. Commercial modules from above mentioned materials are still hard to find. In the table below you will find comparison between different solar cell types with their advantages and disadvantages.
|
Material |
Thickness |
Efficiency |
Colour |
Features |
|
Monocrystalline Si solar cells |
0,3 mm |
15 – 18 % |
Dark blue, black with AR coating, grey without AR coating |
Lengthy production procedure, wafer sawing necessary. Best researched solar cell material – highest power/area ratio. |
|
Polycrystalline Si solar cells |
0,3 mm |
13 – 15 % |
Blue with AR coating, silver-grey without AR coating |
Wafer sawing necessary. Most important production procedure at least for the next ten years. |
|
Polycrystalline transparent Si solar cells |
0,3 mm |
10 % |
Blue with AR coating, silver-grey without AR coating |
Lower efficency than monocrystalline solar cells. Attractive solar cells for different BIPV applications. |
|
EFG |
0,28 mm |
14 % |
Blue, with AR coating |
Limited use of this production procedure Very fast crystal growth, no wafer sawing neccesary |
|
Polycrystalline ribbon Si solar cells |
0,3 mm |
12 % |
Blue, with AR coating, silver-grey without AR coating |
Limited use of this production procedure, no wafer sawing neccesary. Decrease in production costs expected in the future. |
|
Apex (polycrystaline Si) solar cells |
0,03 to 0,1 mm + ceramic substrate |
9,5 % |
Blue, with AR coating, silver-grey without AR coating |
Production procedure used only by one producer, no wafer sawing, production in form of band possible. Significant decrease in production costs expected in the future. |
|
Monocrystaline dendritic web Si solar cells |
0,13 mm incl contacts |
13 % |
Blue, with AR coating |
Limited use of this production procedure, no wafer sawing, production in form of band possible. |
|
Amorphous silicon |
0,0001 mm + 1 to 3 mm substrate |
5 – 8 % |
Red-blue, Black |
Lower efficiency, shorter life span. No sawing necessary, possible production in the form of band. |
|
Cadmium Telluride (CdTe) |
0,008 mm + 3 mm glass substrate |
6 – 9 % (module) |
Dark green, Black |
Poisonous raw materials, significant decrease in production costs expected in the future. |
|
Copper-Indium- |
0,003 mm + 3 mm glass substrate |
7,5 – 9,5 % (module) |
Black |
Limited Indium supply in nature. Significant decrease in production costs possible in the future. |
|
Hybrid silicon (HIT) solar cell |
0,02 mm |
18 % |
Dark blue, black |
Limited use of this production procedure, higher efficiency, better temperature coefficient and lower thickness. |
Popularity: 1%
- SANYO Develops Ultra-thin HIT Solar Cell with Conversion Efficiency of 22.8%
SANYO Develops Ultra-thin HIT Solar Cell with the World’s Highest-level Conversion Efficiency of 22.8% Resource Saving and Half the Thickness of Previous Cells SANYO Electric Co., Ltd. (SANYO) has...
- SANYO With Global Production Strategy for HIT Solar Cell
SANYO Electric Co., Ltd. (SANYO) has recently announced the completion of the third factory building (Bldg. C) of Nishikinohama Factory (Kaizuka City, Osaka), already a mother factory for SANYO’s...
- BiThink – In Search of Bifacial Thin Industrial Multi-Crystalline Silicon Solar Cell
In order for photovoltaic to be implemented on a significant scale, the cost of solar electricity needs to be substantially reduced. This cost essentially derives from the raw material employed...
- Hitachi Bifacial Solar Cell – Key Features
Hitachi manufacturers a unique “bifacial” PV cell as well as several bifacial module styles. While most of the PV module manufacturers use monofacial PV cells in their modules, Hitachi...
Photovoltaic Systems | admin | November 12, 2009
BIPV, green, hybrid, production, SCHOTT, solar, solar cells
