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Lasers application for solar summarized

Lasers in Wafer Solar Cells27th April 2010

Lasers application for solar summarized

Laser Assisted Process: Wafer Solar CellsAdvantages of Laser ProcessNo use of chemical and gases; Clean and GreenWet chemical Plasma

Continuous process compared to PlasmaPlasma: Coined stacked process

Contact-less Processing for thin wafers High Precision Potential to be high throughput

Lasers application for solar summarized

Laser Assisted Process: Wafer Solar CellsKey Factors for Equipment Supplier ConsiderationCost effective Laser sourceDominated by European/US Suppliers

Typical Laser Types under study355– 532nm Short pulse length High Repetition rate High power for beam splitting High speed scanning head

Material HandlingFast Throughput< 1s per wafer

Good grasp of laser process knowledge

Lasers application for solar summarized

Lasers Application OverviewWafer Solar Cells

Junction Isolation

Efficiency Improvement

Contact-less Process

Edge IsolationContact Isolation (Back contact)

Selective Emitter

LGBC

Back Contact

Laser Printing

Laser Dopant Diffusion

MWT

Laser Soldering

LCP

LFC Laser Fired Contacts LFE Laser Fired Emitter

Dielectric Ablation

EWT

Lasers application for solar summarized

Junction Isolation - Edge IsolationPhosphorous diffusion process will result a shunt at the edges Edge Isolation remove electrical connectivity between front and back Isolation can be thru’ front or back 3 Common MethodsWet Chemical Dry Plasma Laser

Lasers application for solar summarized

Junction Isolation - Edge IsolationTypically DPSS Lasers Lower wavelength is preferred; 355 - 532nm Lower surface and sub-surface damage Lower recombination of molten materials

Lasers application for solar summarized

Junction Isolation - Edge IsolationShunt Resistance> 3K Ohms Good Isolation

Lasers application for solar summarized

Junction Isolation - Edge Isolation

Source: Study on edge isolation of industrial silicon solar cells with water-jet guided laser

Lasers application for solar summarized

Driving Efficiency of Wafer Solar CellsEfficiency Improvement 50MW Solar Cells Line 0.2– 0.3% Efficiency gain leads to 1.2– 1.8% Revenue gain

Lasers application for solar summarized

Lasers in Efficiency ImprovementEfficiency Improvement1. Laser Grooved Buried Contact (LGBC) 2. Laser Assisted SE (Selective Emitter)Dielectric Ablation (Diffusion Masking) Lasers Dopant Diffusion

3. Lasers Fired Contacts (LFC) 4. Wrap throughMetal Warp through Emitter Warp through

Lasers application for solar summarized

LGBC: Laser Grooving Buried ContactsBP Solar was the early adopters: Saturn Lines Currently efficiency improvement program is an extension of LGBC ConceptReduce Shadow losses Reduce contact resistance Reduce surface re-combination losses

Lasers application for solar summarized

Laser Dielectric AblationDouble Diffusion1st low doping 2nd high concentration

Ablation70– 80nm of SiN/SiO2 Emitter layer 200nm

Seems to be a Modified LGBCShallow Openings No deep channels

Lasers application for solar summarized

Laser Doping (Laser Dopant Diffusion): SEApplication of dopant on the solar wafer Laser to melt and diffused at selected area

Lasers application for solar summarized

Laser Doping (Laser Dopant Diffusion): SE3 TypesDry Wet Gas

Lasers application for solar summarized

Laser Fired Contacts - LFCBack Contact Alloying for PERC (Passivated Emitter& Rear Cell) Typically for Thin Wafers<170um wafer thickness

ObjectiveReduce recombination losses Internal rear reflecti

on for efficiency improvement Possibly no firing of Al to prevent warpage

Passivation between the wafer and the Al BSFPassivation: SiO, SiN which is insulating

Use of laserAblating the oxide layer Fusing the Al to silicon to make it conductive at the rear

Lasers application for solar summarized

Laser Fired Contacts - LFCConventional Solar Cells PERC: Passivation emitter and Rear CellsSiN Conventional Cells Diffused Layer P/N type Silicon Al BSF SiN Diffused Layer PERC Local Alloying Conductive Path P/N type Silicon Thermal Oxides SiN Al BSF Lasers Contacting and alloying

Lasers application for solar summarized

Laser Fired Contacts - LFCEfficiency enhancement with different rear side passivation stacks

Lasers application for solar summarized

Laser Fired Contacts - LFCTypical Process Flow

Lasers application for solar summarized

Laser Drilling: Back Metal ContactsMWT: Metal Warp Through EWT: Emitter Warp Through

Lasers application for solar summarized

Laser MWT: Metal Warp ThroughRoute the front contact to the rear of cell

Lasers application for solar summarized

Laser MWT: Metal Warp ThroughTypical Holes Arrangement3 rows 17 -24 holes/row 100um size

Cells Module

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