Electroless Silver Plating as a Tool for Enhancement of Efficiency of Standard Industrial Solar Cells
Outline Short introduction to ISC Konstanz Plating on standard industrial solar cells Electroless Ag-plating Principle Comparison to electrolytic (light induced) plating Experiments & results Summary and outlook
Short introduction to ISC Konstanz
ISC Konstanz location 3150 km
ISC Konstanz Konstanz location at Lake of Constance
ISC Konstanz Legal aspects and sponsors full name International Solar Energy legal form registered non-profit association founded on 12.12.2005 institute headed by a Board of Directors elected by the General Assembly consisting of all regular members (individual persons) supporting members (companies / institutions) consult the Board of Directors via an Advisory Board
ISC Konstanz Our focus R&D platform test platform training and education crystalline silicon photovoltaics training of staff in solar cell and process technology silicon feedstock testing of feedstock crystal growth / thin film and wafering education of PV experts in crystalline silicon solar cells cooperation with universities industrial solar cell development novel solar cell generation independent expertise for novel production technologies testing of production PV industry and the public cell characterisation and simulation equipment
Short introduction to ISC Konstanz Plating on standard industrial solar cells
Plating on Standard Industrial Solar Cells Isotexturing POCl 3 emitter-diffusion Edge isolation PECVD SiN x Screen printing Co-firing p Ag-plating
Plating on Standard Industrial Solar Cells Isotexturing POCl 3 emitter-diffusion Edge isolation PECVD SiN x Screen printing Co-firing p Ag-plating in-line wet-chemical
Plating on Standard Industrial Solar Cells Isotexturing POCl 3 emitter-diffusion Edge isolation PECVD SiN x Screen printing Co-firing n + p Ag-plating
Plating on Standard Industrial Solar Cells Isotexturing POCl 3 emitter-diffusion Edge isolation PECVD SiN x Screen printing Co-firing n + p + Ag-plating in-line wet-chemical or plasma-etching
Plating on Standard Industrial Solar Cells Isotexturing POCl 3 emitter-diffusion Edge isolation PECVD SiN x Screen printing Co-firing n + n Ag-plating one sided 70 nm
Plating on Standard Industrial Solar Cells Isotexturing POCl 3 emitter-diffusion Edge isolation PECVD SiN x Screen printing Co-firing Ag-plating n + n Ag Al
Plating on Standard Industrial Solar Cells Isotexturing POCl 3 emitter-diffusion Edge isolation PECVD SiN x Screen printing Co-firing Ag-plating n + n p + Ag Al
Plating on Standard Industrial Solar Cells Isotexturing POCl 3 emitter-diffusion Edge isolation PECVD SiN x Screen printing Co-firing ( Rear side protection ) n + p + Ag Al Ag-plating screen-printing of removable mask
Plating on Standard Industrial Solar Cells Isotexturing POCl 3 emitter-diffusion Edge isolation Ag PECVD SiN x Screen printing Co-firing ( Rear side protection ) Ag-plating n + p + Al Ag
Plating on Standard Industrial Solar Cells principle decrease specific resistance of finger grid by - deposition of metal into the pores - deposition of pure metal on top - closing of contact gaps (constrictions) and thus - decrease line resistance / series resistance R S / increase fill factor or (in case of holding line width) - increase J SC by reducing finger width / shadowing (in case of holding line resistance / series resistance R S ) or - do something between find optimum grid design for a specific line resistance / finger width combination
Short introduction to ISC Konstanz Plating on standard industrial solar cells Electroless Ag-plating Principle
Electroless silver-plating principle R (reducing agent) Na + OH - Ag + CN -
Electroless silver-plating principle
Electroless silver-plating principle ph-control C -control R Ag + oxidised Ag - reduction of Ag + / deposition of silver - oxidation of reducing agent - need to control: ph, temperature, concentration of CN and Ag +
Short introduction to ISC Konstanz Plating on standard industrial solar cells Principle Comparison to electrolytic (light induced) plating
Plating on Standard Industrial Solar Cells Comparison to electrolytic plating Plating time Machine type Electrodes Chemicals Rearside protection Suitable initial finger width Finger broadening Required Ag thickness Possible efficiency gain electroless (autocatalytic) (ESM) slow (10-60 min) batch none CN-type not required 80 µm 145 µm (standard) < 5-20 µm 1 5 µm up to 0.4% electrolytic (LIP) fast (< 10 min) inline contact wheel / brush non CN-type by potential bias < 80 µm > 20 µm 10 µm up to 0.4%
Plating on Standard Industrial Solar Cells Comparison to electrolytic plating electroless: pore filling, < 5-20 µm finger broadening electrolytic: bridging, > 20 µm finger broadening electroless: no E-field gradient most uniform metallisation of complex shapes (high throwing power) electrolytic: strong E-Field gradient faster plating at etches compared to recessed areas, bridging
Short introduction to ISC Konstanz Plating on standard industrial solar cells Electroless Ag-plating Principle Comparison to electrolytic (light induced) plating Experiments & results
Electroless silver-plating experiments & results: A & B plating of insufficiently printed cells before after plating
Electroless silver-plating experiments & results: C plating of thin fingers (ESM 100, rear side mask) mean finger w idth [µm] 140 130 120 110 100 90 80 70 60 50 reference 0 10 20 30 40 mean finger height [µm] 15 13 11 9 7 5 reference 0 10 20 30 40 plating time [min] plating time [min] Finger width and finger height vs. plating time (compared to reference)
Electroless silver-plating experiments & results: C plating of thin fingers (ESM 100, rear side mask) 0,00 0,7 gain in Voc [mv] -0,05-0,10-0,15-0,20-0,25-0,30 0 10 20 30 40 gain in Jsc [ma/cm²] 0,6 0,5 0,4 0,3 0,2 0,1 0 0 10 20 30 40 plating time [min] plating time [min] Voc and Jsc vs. plating time (reference: 612 mv, 33.0 ma/cm²)
Electroless silver-plating experiments & results: C plating of thin fingers (ESM 100, rear side mask) 2 0,6 gain in FF [%] 1 0-1 -2-3 -4-5 0 10 20 30 40 gain in efficiency [%] 0,4 0,2 0-0,2-0,4-0,6-0,8 0 10 20 30 40 plating time [min] plating time [min] FF and efficiency vs. plating time (reference: 74.8%, 15.1%)
Electroless silver-plating experiments & results: C plating of thin fingers - summary for optimum plating time (20 min.) reference thin fingers before plating after plating Finger width [µm] 122 80 102 Finger height [µm] 13.5 7 9.5 Voc [mv] 612 612 612 Jsc [ma/cm²] 33.0 33.55 33.6 Fill factor [%] 74.8 70.8 75.1 Efficiency [%] 15.1 14.5 15.45 no decrease in Jsc?
Electroless silver-plating experiments & results: D plating of standard cells - improved bath ESM 500 lower ph-value rear side-masking is not necessary any more - multicrystalline cells, 156 mm x 156 mm, isotextured, 2 busbars - plating time: 10 30 minutes
Electroless silver-plating before* after plating** Plating condition fast slow medium slow fast Plating time [min] 10 20 20 30 20 Ag-consumption per cell [mg] 30 45 60 100 135 Finger width [µm] 135 140 141 145 147 148 Line resistance [mohm/cm] 235 203 217 193 190 200 Voc [mv] 615 615 616 615 613 613 Jsc [ma/cm²] 32.6 32.7 32.8 32.8 32.8 32.8 Fill Factor [%] 76.0 76.7 76.8 76.9 77.0 76.9 Cell efficiency [%] 15.25 15.4 15.5 15.5 15.5 15.4 * Mean of all, **mean per group No decrease in line resistance? No decrease in Jsc?
Electroless silver-plating experiments & results: E plating of standard cells - improved bath ESM 500 - multicrystalline, 156 mm x 156 mm, isotextured, 2 busbars - plating time: 30 minutes F plating of standard cells with slightly thinner fingers and adapted grid design - improved bath ESM 500 - multicrystalline, 156 mm x 156 mm, isotextured, 2 busbars - reduced finger distance - plating time: 55 minutes
Electroless silver-plating Experiment E Experiment F before after before after Finger width [µm] 143 ± 5 * 147 ± 5 * 122 ± 7 * 125 ± 5 * Shading of grid [% of cell] 7.8 8.0 7.9 8.1 Jsc [ma/cm²] 32.8 32.7 32.6 32.8 Voc [mv] 606 606 607 607 Line resistance [mohm/cm] 200 * 160 * 275 * 210 * Fill Factor [%] 76.4 77.3 77.2 78.1 Cell efficiency [%] 15.2 15.3 15.3 15.55 * Mean out of at least 20 measurements
Content Short introduction to ISC Konstanz Plating on standard industrial solar cells Principle / idea Comparison electrolytic (light induced) plating / electroless plating Electroless Ag-plating Principle Experiments & results Summary and outlook
Summary ESP allows for both - fast (quasi-electrolytic) plating with finger broadening (for cells with reduced finger width) and - slow plating with almost no finger broadening (suitable for standard industrial solar cells) Exp. Finger width before Line resitance before ESP- Bath Plating time Increase in finger width Decrease in line resitance Increase in efficiency [µm] [mohm/cm] [min] [µm] [mohm/cm] [% absolute] C D 80 135 n.d. 235 ESM 100 (rear side masking) 20 10 20 + 20 + 5 + 6 n.d. - 30-15 + 0.35 + 0.15 + 0.25 E F 145 120 200 275 ESM 500 (no rear masking required) 30 55 + 4 + 3-40 - 65 + 0.25 + 0.25 (+ 0.35)* * compared to standard grid design E
Outlook Further R&D ESP prototype batch system installed at ISC - up to 1000 wafers / hour throughput - offline chemical monitoring system Industrial application ESP industrial batch system developed: - industry proven batch platform - up to 3.000 wafers / hour throughput - chemical management by feed & bleed system - online chemical monitoring system - waste water treatment available - complete automation available
acknowledgement: Anders Remgård, Polymer Kompositer, Mölndal, Sweden Thank you for your attention! www.isc-konstanz.de
Electroless silver-plating Pore filling? Fast ion bombardment measurements before plating / after plating
Electroless Ag Impact of Edge Isolation Process - - n+ p-si - - n+ p-si + + p+ p+ Chemically isolated cell Laser isolated cell 3 different edge isolation processes were tested with ESM 500 Ag deposition (laser, wetchemical, plasma) there was no difference in cell results ESM 500 plates selectively on Ag surfaces only No wild growth in grooves or edges No impact on backside Al