Manufacturing Process of Solar Cells/Panels
1) Wet Chemistry - Stage 1
Raw silicon wafers are etched in acid baths to surface saw damage from the wafering/cutting processes done at other plants. The etching leaves a series of pyramid structures on the mono-crystalline surface and this assists light absorption.
2) Diffusion
Wafers are exposed to a phosphorous rich environment which results in a transition layer forming to create a semiconductor device that effectively behaves as a P-N diode in which electrical charges are produced upon absorption of sunlight
3) Wet Chemistry - Stage 2
The glass oxide layer formed during the plasma etching is removed by etching the cell surface in hydrofluoric acid. This leaves the finished surface ready for the screen printing process.
4) Anti Reflection Coating
A thin ant-reflection (AR) coating of silicon nitride is deposited on the front surface of the wafer using a plasma enhanced vapour deposition process. This AR coating reduces light reflection, increases light absorption, a necessary step to ultimately improve the overall light conversion of the future PV cell. The AR process is further beneficial as it injects hydrogen into the silicon to passivate (remove) crystalline defects.
5) Front Print and Dry
A conductive pattern is screen printed into the front wafer surface with silver-rich paste and then oven belt dried to remove solvents and organic binder residue in the silver past. The front conductive pattern forms the busbar that will conduct the photo-electrons.
6) Back Print and Dry
A back print bus bar is screen printed onto the cell’s rear surface using silver rich past. The rear busbar provides the means of soldering and interconnecting adjacent cells to make a solar panel. Finally, the entire rear surface is screen printed with aluminium, a process called Back Field Surface (BSF).
7) Co-fire
The cells are fired at high temperature in a surface at about 800°C. This helps bond the silver and aluminium paste to fuse and bond to the silicon surface.
8) Cell Test
The cells are individually tested for electrical performance under Standard Test Conditions (STC) of 1kW/m2 (1 Standard Sun) irradiance and 25°C. The cells are subsequently graded into specific power bands for future cell stringing to make panels.
9) Tabbing & Stringing
Plated copper wiring strips (tabs) are soldered onto the front of the cells. These tabs form the interconnection for individual cells to be soldered together to make cell strings of positive to negative connections.
10) Laminator
The cell strings are laminated in a vacuum heat press with a layer of toughened glass and ethylene vinyl acetate (EVA) on the front face of the cell string, while on the back side, a layer sheet of Tedlar which acts as a plastic moisture barrier.
11) Panel Tester
Each panel is tested for electrical performance under STC. The panels serial number and test results are printed on the panel label and permanently stored on a panel data base for future reference.
12) Frame
The panel laminate is framed to provide additional structural integrity and a means to mount the panel to structures, building etc.
13) Clean and Package
The framed panel is cleaned and packed for shipment.
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