Efficiency i Industrial Solar Cells Flashcards
What are the most important drivers on PV industry?
- Conversion Efficiency
- Reduction of process costs
How much does efficiency in solar cells increases every year?
By 0.5% - 0.6%
Efficiency of AI-BSF
Limited to <20%
PERC
PERC = Passivated Emitter and Rear Cell
- Local rear contact instead of full rear contact
- Improved electrical and optical performance
- Less recombination and higher internal reflection
- Efficiency up to 24%
PERC Technology - Texture
- Removal of Saw damage which would reduce charge carrier lifetime
- Improve optical Absorption
- Reduce Reflection
- Piramids with a 45 angle on monocrystalline
- Inline and Batch type system
PERC Technology - Cleaning of Surfaces
- Removal of organic and inorganic impurities before high temperature processes
- Microelectronics: RCA cleaning (Radio Corporation of America)
- Photovoltaics: Simplified and cheaper cleaning process
PERC Technology - Phosphorous Diffusion
- Diffusion of POCI3 at 80 degrees
- Creation of phosphorus glass
- Diffusion of phosphorus into silicon
- Creation of n+ layer on front and rear surface
- Tube Diffusion Furnace (Equipment)
PERC Technology - Etching of Rear Emitter
- Single side etch to remove rear PSG and n+ phosphorus diffusion
- Planarization of rear surface
PERC Technology - Removal of Front PSG
- Essential due to its optical absorption
- Etch in HF solution
PERC Technology - Isolation
- Removal of shunt at edges
PERC Technology - Deposition of Rear Surface Passivation Layer
Deposition of a stack of AI2O3/SiN layer
AI2O3
- Excellent passivation layer on p-type silicon
- Reduction of electron density at rear surface
- Low rear recombination
SiN
- Protection against subsequent metallization
- Improvement of internal optical reflection
Plasma-enhanced Chemical Vapour Deposition (PECVD)
- Inline System
- Batch System
PERC Technology - Deposition of Front Passivation and Antireflection Layer
- Deposition of a stack of SiN layer
- PECVD
- Reduction of hole density
- Low recombination
PERC Technology - Laser Contact Opening (LCO)
- Laser ablation of passivation to open contact areas
- Pulsed laser with short wavelength
PERC Technology - Screen-printing of contacts
Screen-printing of metal paste on front (Ag) and rear (AI)
- Metallization of silicon solar cells
- Ag front contact for high line conductivity
-Al as an electrical mirror
Location of Metal Contacts - Front Finger
Collection of electrons from front emitter
Location of Metal Contacts - Front Busbars
- Collection of current from fingers
- Solder region for cell interconnection
Rear AgAl- Pads
Solder region since Al rear metal hard to solder
PERC Technology - Contact Firing
- Contact formation by short high-temperature process 900 degrees
- Firing of Ag front contact throughout SiN layer
- Creation of AI alloy under rear contact points
- Equipment: Inline firing furnace
Monocrystalline Silicon Solar Cell - Size and Output
- Efficiency 22-23%
- Low voltage 0.6-0.7 V
- High Current (9-10 A)
- Series interconnection of cells in module to achieve higher voltage
